||dts-data-start||1279114815||id||type||template||path||image||icon||inset||name||code||idbreadcrumbs||breadcrumbs||currentprice||price||saleprice||headline||label||shipweight||availability||orderable||taxable||leaf||giftcertificate||ypath||contents||abstract||caption||options||keywords||manufacturer||producturl||ean||classification||upc||inyshopping||modelnumber||yshoppingcategory||manufacturerpartnumber||stylenumber||condition||medium||merchantcategory||isbn||style||brand||crosssell||instock||customfields|^^|allelsc||item.||page2||index||||http://ep.yimg.com/ca/I/yhst-73691105158318_2111_621410||||All Electric Scooters||||||||||||||Electric Scooters!||||||||0||1||0||0||||x250 xsooumcoso cosoxbelmo ||||The Ultimate Plug and Play!
Not a fan of gas and oil? These scooters are reliable, resilient and really, really fun! Perfect for kids of all ages all, electric scooters are quiet, affordable and environmentally friendly. There's no measuring, no messy clean up, and no extra expense--the perfect addition to every house or apartment!||||scooter, scooters, electric scooter, electric scooters, 100 watts, 150 watts, 250 watts, 300 watts, 450 watts, 350 watts, 450 watts, 500 watts, 600 watts, 600 watt electric scooter, xcooter, rad2go, ebike||||http://store.thegostore.com/allelsc.html||||||||1||||Sports and Outdoors||||||New||||Electric Scooters||||||||||0||~~|^^|autoresp||ebooks||page2||||||||||Auto Responder Magic||AUTORESP||||||9.950||14.950 ||9.950 ||Autoresponder Magic||||0.000 ||||1||0||0||0||http://thegostore.com/public/AutoResponderMagic.html||||||
||||||||http://thegostore.com/public/AutoResponderMagic.html||||||||1||||books||||||||||||||||||||0||~~|^^|busescve1||item.||page2||scprid||||http://ep.yimg.com/ca/I/yhst-73691105158318_2111_626307||||Building A Self-Balancing Scooter, Version 1||||scprid > ||Scooter Project Ideas > ||||||||Do-it-yourself scooter project:||||||||0||0||0||0||||||By Trevor Blackwell||
Building a Balancing Scooter, Version 1 by Trevor Blackwell
Self-balancing scooters, like the Segway™ are often thought to be technological miracles, but it is not actually very hard to build one. I built the one described here in about a week using off-the-shelf parts. I spent another week tweaking the high-speed stability, improving the steering control, and writing about it.
Although the Segway has several exotic components, mine is built from common low-tech parts like wheelchair motors and RC car batteries. The parts, even at small quantity retail prices, cost less than half of a genuine Segway. It also doesn't need complex or high-performance software. The first version was written in Python and used serial ports to talk to the gyroscope and motor controller. The current software, now in C running in an onboard 8-bit microcontroller, is only 500 lines of code.
Riding the scooter is definitely fun. Things I like about it are:
It's easy, when riding down the street, to stop and chat. Somehow on a bicycle or a regular scooter, it's a huge nuisance to stop. But on this scooter, it seems very natural to pull up and chat while standing on it.
It's pretty easy to drive around inside the office. The low-speed maneuverability makes it easy to go through doors.
Things I don't like are:
It's fairly tiring to ride. Standing still on a hard, bouncing platform makes my feet tired. Not as bad as rollerblading, but a somewhat similar feeling. The body is really evolved to be in constant motion, and the combination of static posture (even more static than standing normally, since you try to keep your weight centered) and being jolted by bumps is probably bad for your spine.
I feel like a total techno-dweeb riding it around. It just screams "Silicon Valley nerd," even more than having 3 cellphones and a PDA strapped to your belt. OK, I am in fact a Silicon Valley nerd, but I don't want everyone to know it.
I get stopped every few blocks by someone ask about how it works. I don't mind telling people about it, but it does take an awfully long time to get to the coffee shop and back in the morning. And I can't quite drink a cup of coffee on it while moving at any speed, so the net result is that I arrive back at the office, 30 minutes later than if I'd just walked, with a cold coffee. A small sacrifice for Science.
Its speed and terrain handling is an uncomfortable middle ground between walking and bicycling. When walking, I usually go in pretty straight lines, over grass and curbs. Biking is fast enough that I don't mind going around on the road. But the scooter is neither fast enough to make going the long way round feel right, nor maneuverable enough to go up and down a lot of curbs.
It's not relaxing and conducive to having deep thoughts the way walking is. Riding it is fun but tense.
Rolls Royce vs Model T
The Segway is made with quite high-quality, high-tech, and expensive components. Overall, the components I used are a lot lower-tech and cheaper than the ones in the Segway. Yet, mine seems to ride just fine. It suggests that there's room for a Henry Ford of balancing scooters to develop and sell a low-cost everyman's version. Here's a quick comparison. Quotes below are from segway.com.
Segway
My Scooter
Motors
Brushless servo motors with neodymium magnets. "The highest-power motors for their size and weight ever put into mass production".
"Like a precision Swiss watch". Engineers designed the "meshes in the gearbox to produce sound exactly two musical octaves apart."
Part of the wheelchair motor above. When going up a ramp, they sound kind of like the starter motor on my old Dodge Dart. Rrrrr-rrrr-rrrr-rrrr.
Batteries
2, 60-cell custom-designed NiMH packs producing 72 volts. "the highest power of any currently available chemistry".
20, 6-cell NiMH packs made for RC cars. They have "IDEAL SOLUTION FOR RC TOY" printed on them.$15 each from Powerizer.
Wheels
Wheels are "sophisticated engineering-grade thermoplastic." Tires by Michelin, with a "unique tread compound (a silica-based compound instead of traditional carbon-based materials)".
Wheels are stamped steel. I think they're made for utility trailers. Tires made by Cheng Shin tire works. They make startlingly loud squelching sounds on tile floors. Tire and wheel are $79 each from NPC, and hubs are $20 each.
Controller
"Sophisticated controller boards from Delphi Electronics" with "Texas Instruments digital signal processor, monitoring the entire Segway HT system and checking 100 times per second."
An 8-bit microcontroller from Atmel, running code written in C using floating point arithmetic. It sends speed control commands out the serial port at 9600 baud in ASCII to the motor driver. $10 from Digikey.
Motor Driver
"a set of 12 high-power, high-voltage field-effect transistors (FETs)".
The controller has 16 MOSFETs and can handle way more current than my batteries can supply. Made by RoboteQ, it's $485 from Robot MarketPlace. It's a popular part for use in Battlebots.
Gyroscope
"packed with five solid-state, vibrating-ring, angular-rate sensors"
One ceramic rate gyro, of the same kind that's in your camcorder (to detect your hand jiggling and stabilize the video) or RC helicopter (to stabilize the tail), and a 2-axis accelerometer to correct for drift. $149 from Rotomotion complete with the Atmel microcontroller.
Structure
Plastic and aluminum in smooth swooping shapes. "Chassis withstands 7 tons of force."
Two pieces of aluminum plate with holes drilled in them, and a standard aluminum extrusion for the handle.
Safety features
Everything is dual redundant. For example, "in the unlikely event of a battery failure, the system is designed to use the second battery to operate the machine and allow it to continue balancing until it is brought to a safe stop."
There is no redundancy or backup system. It is not even robustly made. Loose wires literally dangle out the bottom. In the fairly likely event of the software crashing, a wire coming loose, a component failing, or the batteries running low, the wheels will stop and the entire kinetic energy of the system will be used to accelerate my head toward the ground.
Despite being able to build my own, I'm still impressed with the Segway™ and with the courage it takes to bring such a product to market. Like with cars, it's pretty easy to put together a motor and wheels and make it go. But building a safe, comfortable vehicle is a serious effort.
Warning
There is one very important difference between what can be built as an experiment and the commercial Segway: The commercial one has a lot of safety features, redundancy and fool-proofing. Mine has none whatsoever (Well, it does have a kill switch so it doesn't go zooming away if I fall off, and it does shut down if it finds itself tipped more than 45 degrees.) This is pretty darn important, and you should think about it very carefully before considering building such a thing yourself. With a scooter like this, if it stops working for any reason (software crash, hardware failure, low battery) you will fall, hard, and probably on your face. Imagine zipping along at 10 MPH, and suddenly the platform you're standing on stops dead. Oh, and there's a T-bar in front of you to trip you up if you start to run. So you really shouldn't try to replicate this experiment, and I can't be responsible for what happens if you read this and try to build something.
A scooter that you ride on is not the best place to learn how to build a two-wheeled balancing device. Getting them working properly is quite subtle, so you should really start with a two-wheeled balancing robot and then scale up. See my notes on safety if you're considering trying to build something.
Another caveat: I am not a lawyer, but beware that the Segway folks have a US patent on the whole idea of a balancing scooter. Note that this is not a set of instructions for building one, it's just notes on how I built mine. I built this one for my own amusement and to satisfy my personal curiosity about how balancing scooters worked, but in the US building such a thing with any kind of commercial motive without a license from the patent holders could get you in legal trouble.
Construction
The mechanical construction is incredibly simple. Just a plate to stand on bolted to the tops of the motors, a support across the bottom, and a handle. Hanging from the foot plate are two pieces of hand-bent sheet metal to support the batteries. The batteries are just taped and cable-tied to the sheet metal.
Mechanically it's much simpler than any other kind of vehicle. With only two wheels side-by-side, there is very little structure. With no steering it doesn't need complicated pivots and linkages. It is literally just two motors bolted to a frame and a stick to hold.
The electronics and footrest all fit entirely within the 14" wheel diameter. Without the handle, it can roll end over end. But the ground clearance is pretty small. I should go up to 16" wheels, hopefully a bit lighter than the big tires I've got now. Currently it weighs about 90 lbs with its full load of batteries. The wheels alone must account for 20 lbs of this.
Dashboard
The dashboard is an electronics chassis box with knobs for steering and balance feedback loop gain. This shows the early version of the dead man's switch, which really is not adequate. I found this out when I fell off, but the wire pulled apart instead of yanking out the connector. When it pulled apart, the exposed strands ended up touching to complete the circuit and keep it going. Fortunately, a safety feature in the software shut it down before it ran over my head.
Power
The motors I used are made for wheelchairs where they are driven from a 24 volt battery. I want a little more speed, so I drive them from 36 volts. My wheels are also a bit larger than the wheelchair's. It should reach 15 MPH flat out. I got 36 volts by putting 5 standard 7.2 volt RC car battery packs in series. The batteries are rated for 30 amps discharge and I wanted over 100, so I put 4 strings of 5 in parallel for a total of 20 packs or 120 cells.
There is a a complication with multiple NiMH batteries in parallel. You want to avoid current flowing between them when their voltages are a bit different. So there is a bridge rectifier for every pair of batteries, with both + and - terminals connected to the motor driver. That way the voltage on the 4 strings of batteries can differ by up to 1.5 volts without current flowing.
The batteries can be disconnected by the 4-way connector for safety, and for charging. I use an Astroflight model 112 charger, which delivers 5 amps charge current at the 40 volt charging voltage. See schematic diagram.
The system pumps energy back into the batteries when it's decelerating or doing downhill. I had worried about the frequent current reversals harming the batteries, but I'm assured by a number of people who've had experience doing this with NiMH batteries that it works well. There might be some extreme case, like starting at the top of Pike's Peak and riding all the way down, where it could overcharge and destroy the batteries.
Balance and Control
Balancing is easy. Just keep the wheels under the center of gravity. It's just like when you pick up a stick and balance it resting on the palm of your hand.
Actually, there are some complications. You don't know where the center of gravity is. You don't know exactly which way up is. And you may not be able to move the wheels fast enough to keep under it.
I discuss knowing which way is up under "Gyroscope" below, but for now assume it's known. Technically what it knows is the angle between the scooter's chassis and the direction of gravity. And instead of keeping the wheels below the center of gravity, it keeps the stick vertical (ie, the angle equal to zero.)
With the stick vertical, if you stand in just the right position, the center of gravity will be right over the wheels and the scooter will be stable. But if you lean forward, the center of gravity will be in front of the wheels and the scooter will start tipping forward. The computer senses this and moves the wheels to keep the stick vertical. But by then it has fallen some more, and it needs to move the wheels faster.
The net result is that when you lean forward, the scooter accelerates forward and when you lean back it accelerates back. It's surprisingly intuitive. Most people find they can control it within seconds of getting on it. If you're used to riding busses or subways, you're used to leaning forward when the bus is about to accelerate. Well, this scooter follows your lean instead of you having to follow it.
There is another complication. What happens if you keep leaning forward until the scooter is going so fast that the wheels can't keep up? It has to change the tilt of the scooter so instead of keeping the bar vertical, it tilts back. The bar is at waist level, so it pushes you back until the center of gravity is no longer in front of the wheels and it stops accelerating. If you lean farther forward it keeps tilting back in order to keep the speed down. In order to be able to tilt the scooter back it needs to speed up the wheels and get them out in front, so the speed limiter needs to kick in before the motors are maxed out. I currently have the limit set to 50% of maximum speed.
Keeping the Stick Vertical
Keeping the stick vertical is easy. If it tilts forward, it runs the wheels forward until the bottom of the stick is under the top.
Here too there are complications. It has to move the wheels just the right amount forward. Too much and it'll have to move them back, then forth, until the thing is bucking widly. This is pretty much the default thing that happens until you get it tuned just right.
It needs to know both the angle of the stick and how fast it's changing. Knowing how fast it's changing lets it slow down before it overshoots the mark. Technically this is known as a PD loop. The amount of drive it sends to the wheels is proportional (P) to the error in angle, and also to the derivative (D) of the error.
I mentioned above that when it's going too fast it needs to tilt the stick back. This is tricky to do, because in order to tilt back it needs to accelerate the wheels forward to get them a few inches out in front. It then seems like it's going even faster, and it tries to tilt even farther back. This is called "positive feedback" and it's a recipe for uncontrollable oscillation. Making this stable was the trickiest part of the whole project, and the fact that it can only be tested at high speed resulted in several moments of terror and a few bruises before I got it right.
Wheels and Steering
Steering is done by making one wheel go faster than the other. Because all the mass is centered between the wheels, it can spin around quite quickly.
When not moving, maximum turning corresponds to having one wheel at about 10% forward and the other at 10% reverse. This spins it around pretty fast. You wouldn't want to turn this fast at high speed because it would tip sideways, so it reduces the maximum turning speed as the forward speed increases.
The wheels have 0.5 degrees of toe-in, meaning that they are both angled slightly inwards. The front wheels of most cars have a similar amount of toe-in. Pneumatic tires are inherently flexible sideways, and it makes it more stable to have them always flexed slightly. I don't know if 0.5 degrees is the right amount and I haven't tested any alternatives. But the steering is quite stable despite not having any active correction in software.
Putting it all together
What takes many paragraphs to explain is surprisingly simple to code. Here is the basic pseudocode of the balance algorithm, complete with the numbers which made my scooter feel stable and responsive.
Inputs
angle, angle_rate: the tilt angle of the scooter in radians and its derivative in radians/sec steer_knob: the reading from the steering knob, between -1 and +1.
left_motor_pwm and right_motor_pwm directly set the duty cycle of the pulse width modulator for the wheel controller, and range from -1 to +1 (+1 is 100% forward, -1 is 100% reverse.)
Gyroscope
In order to keep the handle vertical, it needs to know which way is up. Humans, other mammals, and even lobsters have a nifty little sensor in the inner ear which does this, and it's possible to do something similar mechanically. The simplest way to know which way is up is with a pendulum. A pendulum at rest points down.
Unfortunately, the scooter is not at rest. If it's accelerating forwards a pendulum will swing backwards. It may also get swinging back and forth. It needs a much more stable notion of up.
A gyroscope made from a spinning wheel is the classical solution to keeping a vertical reference. They are still used in airplanes to remind pilots which way is up when they're in the clouds. But having an actual spinning flywheel is clumsy. They take time to spin up, they need expensive precision bearings and lubrication and use a lot of power, and occasionally the flywheel explodes (they have to spin pretty fast) and sends little bits of shrapnel into the rest of the system.
Although it's hard to visualize, it turns out that if you have a tuning fork vibrating and rotate it, it will cause a measurable vibration in the perpendicular direction. By measuring the vibration you can tell which way it is rotating and how fast. The scooter uses a very small ceramic tuning fork in just this way. Fortunately, I didn't have to make a tiny ceramic tuning fork on a tiny pottery wheel. They are a standard electronic product called a piezoelectric rate gyro. They're used in handheld camcorders to detect your hand jiggling and subtract out the motion from the picture to make it stable. One of the first successful applications of nanotechnology, they're a vital enabling technology for TV shows like C.O.P.S.
Unfortunately, these rate gyros are not perfect. They tend to report a small rate of rotation even when they're perfectly still. And if the balancing software integrates this small rate for long enough, it'll think it has rotated a lot. So it needs to compensate for that, and it does it with a pendulum. While a pendulum may swing around and wobble back and forth in the short term, the long-term average of its position is straight down.
Again, it doesn't use an actual pendulum. It uses a "micromachined silicon accelerometer", a silicon chip with a sort of diving board etched into it. This diving board bends a tiny amount in the direction of gravity, and some electronics detect how much it bends. With two of these arranged perpendicular to each other, it can compute the angle of gravity by computing the arctangent of the ratio of the bending measurements. And unlike a pendulum they don't get swinging around.
So now it has to combine the short-term reading of the rate gyro and the long-term reading of the pendulum. There is a theoretically optimal way to combine these pieces of information into a good estimate of actual tilt angle. This is called a Kalman filter. Such a filter was a good place to start, but I found I got better results with a hand-tuned feedback loop.
Sound complicated? It's not as bad as it sounds. In fact, the whole code, including stuff to read ADCs and manage serial communication is about 500 lines.
Microcontrollers
All the software needs somewhere to run. Not so long ago this task would have required more computer than you could lift, but now it runs in a tiny chip costing $10. The one I used is from Atmel. They're fast and very easy to write software for; I wrote the code in C using floating point arithmetic and trigonometric functions, and it has plenty of speed for this kind of application.
The Atmel chip I'm using has built in analog data converters to interface with the gyroscopes and steering controls so it's a nearly complete solution. There are only about 5 chips in the whole scooter.
Motor driver
The software needs to exert precise control over the speed and torque of the motors. Under worst-case conditions, like going fast up a steep ramp, the motors need to work very hard to keep up and can consume a tremendous amount of power doing so, as much as 5000 watts.
The torque generated by the motor is directly related to the current flowing through the motor. The current is controlled by alternately switching the motor across the full battery voltage, then short circuiting it. If it did this slowly it would do just what you'd think: alternate full speed, then full stop. But it alternates very fast, about 4000 times per second, and this produces a smooth output from the motor. If it spends 37% of the time with the motor connected to the battery, the motor runs about 37% of full speed.
The scooter uses a device made by RoboteQ to switch all this power around. It's a popular unit among Battlebot builders since it's small and handles a lot of power. It receives commands from the microcontroller over a serial port, such as "left motor 37% forward, right motor 35% forward" (but in a compact binary format) and it gives the motors that much power. This command would correspond to going about 5 mph in a gentle right turn.
Limits
In theory, balancing is quite simple. Just keep the support under the center of gravity. Where it gets complicated is in handing the limitations of the motor & battery system. The simple control strategy may require much more power than the motors & battery can deliver. If it lets the scooter get into a situation where the wheels can't keep up with the center of gravity, the rider will be thrown.
If you're going fast and then run into something like a ramp or speed bump, it may require a lot of power for a short time to keep the wheels going up the ramp. As batteries get low and motors get warm, the amount of available power goes down. It's hard to predict exactly when it doesn't have enough to run safely. There's certainly a large gap between when it couldn't handle hitting a speed bump at 10 MPH and when the batteries actually run down.
I plan to experiment with using a bank of capacitors to provide enough short-term oomph to handle hitting a major bump at high speed. It's much easier to calculate the amount of energy needed to handle a bump safely than the maximum speed for a given battery condition. It just needs enough to get the wheels out ahead of the center of gravity, so it can slow down. My back-of-the-envelope calculations suggest about 2500 Joules delivered in 0.5 seconds. The new carbon aerogel ultracapacitors (not to be confused with mere supercapacitors) can store this much power in small 4" x 4" x 2" package costing about $250.
Or, I could just stick a wheel in front of it. But that would seem like something of a compromise.
Performance and Testing
When I first built this, I had never been on a Segway or even seen one close up. You'd think with all my geeky friends I'd know someone with one, but I didn't. I tuned the system according to how I thought it should work. A few days after I put up this page, I got to try a genuine Segway and I realized two things: it felt better to have a stiffer feedback loop so the handle didn't move back and forth so much, and that it should limit maximum speed by tilting back. I changed both, and it feels much better now. These videos are from the original version:
I'll try to get some videos of the current performance up soon. It still doesn't quite match the Segway in two respects. First, my gyroscope drifts a bit especially when accelerating hard or going up a ramp, so the handle position wanders around a bit. This is tiring on the arms, and makes it harder to limit top speed. Second, my balance feedback loop isn't quite as stiff as the Segway's, so it still feels a bit mushy. I can't make it any stiffer without getting oscillations. It may need a higher-performance gyroscope, but I think the main difference is that the Segway's wheels have a large moment of inertia which allows it to apply a reaction torque to the chassis. My wheels are smaller and have most of the mass in the center, so it only gets reaction torque between the ground and the mass of the scooter body. The soft rubber tire adds a large spring between the wheel and the ground, and the mass of the scooter is not very stiff either since the batteries flop around.
The Segway is also bigger, stronger, lighter, and has more ground clearance and battery power. But I still like mine pretty well.
Cupholder
I like to use the scooter to go for coffee, but it's very hard to hold onto a cup of coffee and ride it at the same time. It needed a cupholder. I tried a very simple design, basically some cable ties on the main bar, but it didn't work well. I lost about 3/4" of coffee in 1/2 mile and got coffee spatters all over my pants. But, the great thing about publishing your experiments is that you get lots of minds thinking about the problem and one of them will probably suggest the right answer. Bob Beichner, from the physics department at North Carolina State University, wrote:
...all you have to do is make a little "hammock." Take a large drink coaster or other disk and drill three small holes near the rim, 120 degrees apart so they are equal distances apart. Run a string through the holes and tie together a foot or so (the distance depends on the size of your cup and the coaster diameter) above the center of the coaster. Support the hammock from the knot where the strings come together by hanging it on a hook or something. As long as the coaster doesn't bump into anything (it has to be able to swing freely) it is pretty hard to spill anything, regardless of how you move around the knot. You can even spin the thing in a big vertical circle so the cup is sometimes upside down, and nothing comes out. (Hopefully you won't do that with your scooter!)
Sure, I thought, in theory. I think I saw that demo in Physics 101 too. But it can't possibly work in practice, with 3D wobbling, swerving and bumping. With no damping, the cup will swing around wildly. But, I tried it anyway. Instead of the plate Bob suggested, I used a large cup that a normal coffee cup will fit into. As well as keeping it from sliding off when it's jiggling up and down, it should also help keep the coffee warm in the fast-moving air. As a worst case test, I just filled it with water and put no lid on.
The first version used a string about 30" long. It worked as long as the cup didn't bump into anything, but the string was so long that it was hard to avoid hitting obstacles or the scooter itself. For version 2 I shortened the system to about 14" including the cup and hung it about 15" out in front of the handlebars. It swung around crazily, but didn't spill. It's quite amusing to watch: it looks wildly improbable and out of control.
These are the things that are currently bad about my prototype.
The ground clearance is very low. Even large acorns get stuck under it. Using larger wheels is one solution, and I think with more clever mounting of batteries I could get them at least 1.5" higher. If I make the wheels much larger, I'll want to find a way of getting the foot plate below the center of the wheel since I'm already 8" off the ground.
It should detect when I've stepped off it, so it doesn't simply zoom away with no rider. My big worry is that I'll shift my feet around and it will erroneously detect me having stepped off. At high speed, this could be Really Bad.
It really should give some indication of battery charge, other than by falling over when it gets too low. The voltage of NiMH batteries isn't a good indication of charge, so there's no easy way to do it.
It doesn't detect when the wheels are off the ground or slipping. Once when leading it down a curb, I got it twisted a bit and it hung up on the battery supports. With the wheels free, they started spinning very quickly and it gave a huge lurch when it got back on the ground. I don't know what the general solution is. Probably it should limit the speed to 1 MPH when the rider is off.
Things Learned
You don't need high-tech low-inertia motors for adequate responsiveness. Regular old copper-wound motors work pretty well even though they have a lot of rotating mass that acts like a flywheel. This might actually help with handling a bump, as the inertia helps keep the wheels spinning up the incline.
You don't need low-backlash gearboxes either. The conventional non-precision spur gear units give about 1/8" backlash at the wheel diameter. You can feel a tiny clunk sometimes when the torque reverses, but it's hardly noticeable. They do make some gear whirring noise which is noticeable indoors. It'd probably be quieter if they weren't bolted to a big aluminum sounding board.
I didn't need any feedback in yaw (left-right steering) to keep it heading straight. I just give equal motor drive voltages, and it keeps nice and straight even on slopes or going over bumps.
Future Work
Things I'd like to try, if I had more time:
I can take both hands off the control bar and control with my feet, at least at low speeds. Handy when going through doors. I wonder if I could learn to control it without a handlebar at all. Perhaps with some sort of ski boots & bindings for greater control.
Put the vertical handle bar off to the side, instead of in front, and hold it with one hand.
Make wacky new vehicles on the same principle. Why not go for coffee in a miniature dragster, doing a wheelie all the way? Or in a greco-roman chariot, without the horses? You could also make improbably tall vehicles, like a phone booth that zoomed around upright.
Take a regular 3-wheeled "mobility scooter," and make it do wheelies all the time. You might even be able to use its original motor driver, and just add a gyroscope and feedback controller. Seeing one of those 3-wheeled scooters, normally associated with geriatric mall cruisers, doing a wheelie would really surprise people. And if it fell, you'd at least have a wheel to land on.
The ideal vehicle might be something that rides like a motorized recumbent 3-wheeled bike on roads, but tilts back to balance on sidewalks. You'd have to get off to change modes.
Build one with a small gas engine and generator instead of batteries to power the electric motors. It'd probably need a substantial capacitor bank to smooth out the power demand. The engine and alternator might even be lighter than the batteries, and it'd have tremendous range. It might go faster too.
Build a balancing scooter without any batteries at all, but instead control the braking force on the wheels to keep it balanced. It would only work going down a hill. You could use the same motors and dump their power into a bank of big resistors. Mountain boarders might dig this.
Build a real experimental platform with 20 or so knobs to control each of the feedback parameters. It's very interesting to adjust a parameter and feel the difference in real time under your feet. It'd need to have some fail-safe scheme for returning to a reasonable set of parameters if the user adjusts them too far.
||||||||http://www.thegostore.com/busescve1.html||||||||0||||Sports and Outdoors||||||New||||Scooter Projects||||||||||0||~~|^^|busescve2||item.||page2||scprid||||http://ep.yimg.com/ca/I/yhst-73691105158318_2111_726569||||Building a Self-Balancing Scooter, Version 2||||scprid > ||Scooter Project Ideas > ||||||||Do-it-yourself Scooter Project:||||||||0||0||0||0||||||By Trevor Blackwell||
Balancing Scooter Version 2 By Trevor Blackwell
The original balancing scooter I made in late 2002 had some shortcomings, so in January 2005 I set out to make a better one. Version 2 is faster, lighter, smoother, and has more range. It has 3 inches more ground clearance, it's an inch narrower so it fits through doorways better, and it has a much better steering system.
Version 1
Segway i-Series
Version 2
Speed
9 MPH
12.5 MPH
15 MPH
Weight
90 lb
80 lb
70 lb
Steering
touch pads
twist grip
handlebars
I was prodded to build version 2 when Chris Johnson brought over his two Segways and we went for a ride. (I had never ridden one any distance before.) The Segway was faster and smoother than my machine. The gauntlet was thrown! I had to surpass it.
As usual, I followed my personal rule for building projects: only use parts that can be ordered over the internet without talking to anyone.
Wheels
Some punk riding it
The first change was larger, lighter, smoother wheels. The original wheels were 14" diameter foam-filled trailer tires. They had fairly high rolling resistance, and one of them had started to make a skrupp-skrupp sound every time it went around where the foam was peeling away from the rubber inside.
I decided to change to bicycle tires. They are lighter and have less rolling resistance than the trailer tires, and the narrower width helps it fit through doorways. To do this, I bought a pair of 20 inch diameter bicycle wheels (rim, hub and spokes) and machined a new hub to bolt onto the output shafts of my motors. I started with a 3.5" diameter by 3" long cylinder of steel, machined the mounting faces, removed 80% of the material to reduce weight, and then drilled 36 holes around the rim to fit the spokes. The diameter of the hub is larger than the original hub to get maximum torsional stiffness of the wheel. After the tedious job of stringing, tightening, and adjusting the spokes for even tension and no wheel wobble, I put on 100 PSI snake belly tires. The 20" wheels propel the scooter 43% faster for a given motor speed than the 14" wheels and give 3" more ground clearance. They also look much better, especially with the all-black smooth tires. The narrower wheels reduce the width by about an inch, making it much easier to get through doorways.
Segway Polo
I may make a second set of wheels and outfit them with knobby mountain bike tires, for playing Segway Polo on grass.
Electronics
I also replaced all the electronics. Version 1's electronics were chosen for maximum convenience. Version 2's electronics are designed for performance. I replaced the dual-channel RoboteQ motor controller with two OSMC controllers. While the RoboteQ is fine for many applications, its use of a 9600 baud serial link for control added too much delay to the feedback loop for good performance. The OSMC controllers take a PWM signal directly from the microcontroller. I also get more precision in the PWM control: 9 bits instead of 7.
Most important of all is how the OSMC lets me precisely control motor voltage, regardless of the condition of the batteries. In the RoboteQ system I couldn't measure battery voltage fast enough to include in the feedback loop, so the gain in the balance feedback loop depended on the resistance in the batteries, which increases as they run down. Fresh off the charger the gain was so high it would start oscillating if you didn't hold the handlebar firmly, and after 3 miles it would start feeling mushy and unstable at high speeds.
In the new system an analog-digital converter in the microcontroller measures battery voltage 2000 times per second, so I can adjust the PWM controller to get a desired motor voltage. It turns out that most of the "clunk" the old one produced as the motors changed direction was due to the electronics, not the gearboxes. The new version feels perfectly smooth.
I also changed the gyro and accelerometer. I had been using a Tokin gyro that came on a board from RotoMotion. It had some performance problems: it would occasionally glitch (causing the scooter to jump), and it was susceptible to vibration (causing the tilt angle to wander at some speeds.) I changed to the CRS03-02 gyro from Silicon Sensing Systems. Noise is lower and it seems completely immune to vibration. I'm also using the ADXL105 accelerometer instead of the ADXL102. The difference is that it has a higher saturation threshold (5 Gs of acceleration instead of 2) so it's less likely to saturate on bumpy roads.
The new gyro and electronics have a much faster response, allowing tighter control of balance. While version 1 required a firm hand on the handlebar at all times, the new version can be controlled entirely with the feet, even at high speed. You can lean it up against a wall and it will remain almost motionless. (The old one had a tendency to start whacking the wall.) The new gyro also has less drift, so the handle angle of the scooter doesn't wander as much.
Batteries
I also installed better batteries. Version 1 started with 120 cells worth of cheap off-brand NiMH batteries. One bank of 30 caught fire because the fragile plastic shell wore through, and one seems to have a dead cell that won't accept a charge. Version 2 uses 60 HHR-6500 D cells from Panasonic. Digikey part P019-ND. These are high-quality cells with low internal resistance (typically 2 milliohms -- theoretical short circuit current = 600 amps!) I wired them in two parallel strings of 30 for a nominal voltage of 36 volts, able to deliver 200 amps at 30 volts. This works out to 8 horsepower peak. Those pedestrians better get out of my way!
In the original scooter I used a diode bridge to parallel the batteries while allowing some voltage difference between them. In the new version I use a relay to connect both batteries simultaneously when the power is on. This reduces power supply impedance and gives smoother control. Also, the relay disconnects the batteries from each other during charging so I can charge the packs separately. There are two charging jacks on the console.
Remote Control
The scooter is now Bluetooth-equipped. Using a Bluetooth wireless connection, I can can change parameters, download logs, and even drive it using my laptop. I got a pair of serial port extenders from Free 2 Move which look like DB-9 connectors with no wire coming out of them. Within 100 meters range, they provide a transparent serial port connection. Then I wrote a GTK application that lets you drive it around without a rider. I can now leave my scooter parked somewhere and use my laptop to have it come and get me, thus saving valuable steps. All I need now is to make it run on one of those Linux wristwatches, and I'd have the complete
James Bond remote control system. (Or at least a yuppie techno-geek version of it.)
Battery Monitoring
The old version would let you know that the batteries were getting low when the balance feedback would get mushy. The new version measures and compensates for battery voltage and resistance, which is great except that the rider has no way of knowing when the batteries might let him down. So version 2 monitors battery state by doing a least-squares fit between battery voltage and current draw. It calculates the maximum speed at which it would have enough torque to balance properly, and limits the rider to that speed by tilting back. It also has a beeper which sounds when the motor drives are nearly maxed out, or the battery voltage drops below a threshold, or the battery current exceeds the battery fuse rating, or a few other exceptional conditions.
Steering
The Segway uses a twist grip on the left handlebar to control steering. My version 0 used a potentiometer conveninently located where my pants would brush against it and send me into a spin. Version 1 used a pressure sensitive touch pad with left and right sides. This was all right, but required careful finger positioning and wasn't very intuitive for others to learn. Version 2 uses handlebars which you twist. The handlebars don't actually move when you twist them; they sense the torque applied using four strain gauges which measure the slight change in resistance of a thin wire bonded to a piece of metal when the metal bends.
Just to make sure it can outperform Segways in every way, I increased the steering control so it can spin in place much faster than a Segway. It goes around 1 revolution per second. It's pretty terrifying to be on, actually. I'm going to have to add a mode switch: normal (for me), beginner (for letting other people try it) and yee-haw (for proving that it can beat Segways.)
Chassis
To protect the batteries against damage, I added a stainless steel plate around the bottom. It also looks better than the mishmash of wires, plastic sheet, and fiber tape that held the old undercarriage together. The steering column, formerly 1.5" square aluminum extrusion, is now 2" square tubing which is lighter and stiffer, and looks cleaner. Also, all the wires and switches can be mounted internally sticking out the side.
To improve chassis stiffness, some metal bars are bolted onto the front and back of the main plate. It still isn't a very well engineered chassis, but it handle the usual urban terrain (jumping off curbs) pretty well.
Controls
The new version adds a few controls, since I had space for them on the steering column. First is an on-off switch in addition to the kill switch on version 1. That way I can leave the kill switch key on it so it won't get lost, and I don't need to fiddle with the key when I'm parking it. I also added a beeper to indicate dangerous battery/speed combinations, and a knob which I can use to adjust whatever parameter I like.
Styling
Segway owners report being yelled at by people in pickup trucks (and I've gotten this a number of times,) usually something to the effect of "Too lazy to walk, you f***ing homo?" Objectively, it's less lazy to ride the scooter than drive a car. It also uses less fuel, and pollutes the air less. The people yelling from inside their truck aren't walking either. At least I'm standing up. But, like, whatever. I dismiss this part of their criticism.
However, I think something can be done about the "homo" part (not that there's anything wrong with that.) It reflects the not-so-masculine soft plastic styling of the Segway. I'd like to see if I can tweak the styling of mine so I don't get yelled at as much. At least mine is metal, but it still looks spindly. I'd like to give it a muscular look with lots of chrome tubing and polished metal surfaces.
The new wheels are a step in the right direction. After I put them on, the first comment I got on the street was from a hip-hop-looking guy in a Mustang who pulled up and told me, "Dude! That's tight!" Later at the office, I checked Urban Dictionary and found that "tight" means "stylish, cool, having everything together," "dude" means "male person," and "that's" means "that is." So he liked it!
By the way, it's not just any new form of motorized transportation that attracts hostility. I often ride my electric unicycle around, and I've never gotten a negative comment.
Futures
While the new chassis is better, it still isn't great. I'd like to propose an offer to someone with good metal fabrication skills. Make two very cool looking frames, one for me and one for you, and I'll provide the electronics for both. We'll each pay for our own motors and batteries. Or, if the producers of Monster Garage are reading this, I think we could put together a pretty amusing monster-Segway project. I'd picture a big beast capable of 30 MPH, with lots of chrome and bad-ass styling. Maybe some of those spikes that pop out of the wheel hubs, like in Ben Hur. If anyone insults Jesse James's masculinity while he's riding it, he gets to send it off a cliff. (I think it should be able to stay upright all the way down. We could mount a wireless camera right on it.)
How fast can a scooter like this go? There's no fundamental limit. A bigger, heavier one could go highway speed. The danger, of course, is that if something fails it'd be a serious accident. Under 10 mph the rider can probably land on his feet if it falls over, but at higher speed you'd want more protection. Also, the differential steering might be iffy at high speed, and hitting a pothole without any suspension might be hazardous. Someone else with no fear of death should experiment with this.
Q - "How much is shipping?" or "What is the total cost of the scooter?" A - The total shipping cost is shown on every single items's web page, just below the "add to shopping cart" button. [READ SHIPPING COSTS TO CUSTOMER] We ship anywhere in the continental United States for the same price. This is direct to your door; don't be fooled by scooter stores that say "free shipping" but ship to a terminal miles away from your house. Our shipping costs INCLUDE all residential shippings fees and, in the case of motor scooters, a lift gate. TOTAL COST = ITEM COST + SHIPPING COST. That's it, no hidden fees or other charges.
Q - "What is your warranty/return policy?" A - Our warranty is the manufacturer's warreanty; 30 days parts. This means we will pay for any parts needed to fix the scooter during the warranty period. Due to the high cost of shipping, we (like all online scooter stores) do no accept returns and thre are no refunds, except in the rare case of a provable manufacturer's defect. For more on our warranty, please go to our warranty page on the web site- it is the button on the left side that says "Warranty & Shipping" Note we will not accept any returns based on unsatisfactory legal status.
Q - How long will it take the scooter to ship? A - While we cannot gaurentee a scoter will arrive by a certain date, especially during the holidays, normal shipping time is 2-5 business days (5-10 business days for motor scooters.)
Q - When will the scooter I ordered ship/arrive? A - Your order will be sent to the warehouse immediately (except if paying by check, on check orders we wait 10 days for the check to clear.) As soon as the order ships, the warehouse will email us a tracking number that we will sand along to you so you may track your order/coordinate receipt of the scooter.
Q - Is it legal to ride my scooter in the street? A - It is the customer's reponsibility to check with their local DMV as laws vary state to state. Most small scooters may be ridden on sidewalks, most larger (motor scooters) may be rideen in the street, and usually scooters that are 50cc or less do no require a license. All our scooters are DOT and EPA certified. Note we will not accept any returns based on unsatisfactory legal status. Generally all electric scooters are legal and do not reuire any licence (like a bicycle.) Gas scooters are usually considered mopeds. Again, the GO! Store makes no claim about the legality of any item since we ship to all states and all states have different laws.
Q - There is no manual, how do I assemble the scooter? A - Most items have a link to an online version of their manual on the item's web page. If not, they can refer to the manual under "Scooter Maintenance" on our website.
Q - Is item X in stock? A - Everythi ng on our website is in stock unless specifically stated otherwise. Inventory does change quickly though. We will email you if an item you ordered went out of stock before the order reached the warehouse.
Q - Can I cancel the order? A - Only, if scooter has not yet been shipped. To cancel the scooter once the scooter has be shipped, customer is responsible for return freight and a 15% restocking fee.
Q - What is our warranty? A - Thrity days bumper to bumper parts warranty. On "Motor Scooters", there is also a three months warranty on motor and drive train. For more information, see our warranty page.
Q - Do I need a license? A - It varies by state, but generally no, not on the small gas and the electric scooters. Most states considered them "off road" scooters and can be can be ridden anywhere you can ride a bicycle. For "Motor Scooter" category, some states require that you have a motorcycle license and be registered with the state. For more infomation, check with your local DMV.
Q - Do I pay taxes on the scooters? A - Not on the smaller gas and electric scooters, Sales taxe on motor scooters are paid when you register the scooter.
Q - Are parts readily available for the scooters? A - Yes, parts are available through our wholesalers. They are free during our warranty period and may be ordered with a charge after the warranty period has expired.
Q - Can I get a discount? A - If people ask (or you need to do it to get the sale) you may give them a 10% (pre shipping cost) discount by typing "tenpercent" in the "Employee Code (optional)" field during check out. DONT TELL THE CUSTOMERS HOW TO DO THIS! It's just for you to do if someone seems "on-the-fence" about buying. Tell them you can give them a 10% discount if they buy NOW, on the phone.
All other questions will be answered by us within one working day by email to sales@thegostore.com please include the customer's name, email address and last four digits of thier order number if they are a current customer.
OTHER NOTES:
We do not sell parts except to customer who have bought scooters from us.
Most item pages have technical support links for that scooter at the bottom of the page.
For all other questions, the customer may email us at sales@thegostore.com. (or they can use the "contact us" button on left side the web site, near the bottom.)
Everything listed on the store in in stock. In cases where it a color is not in stock, the item says something like "Black (ships 10-30-06"
LARGE SCOOTERS ASSEMBLY REQUIRED: Motor Scooters do require some assembly--- suully attaching the front wheel and side mirrors. We do not accept returns due to incorrect assembly. You may assembly it yourself or have it shipped to a local bike shop to be put together (usually for a small fee.)
COMPLAINTS: For current customers, take thier complaint (and order number if they have it-- we just need the last 4 digits) and their email address, an send it to us at sales@thegostore.com
||||||||||||||||1||||Sports and Outdoors||||||New||||||||||||||0||~~|^^|formopiandin||link.||||||||||||For more pictures and information on the Zenvy, click here||||||||||||||||||||||0||0||0||0||||||||||||||||||||||||0||||||||||||||||||||||||0||~~|^^|forkids||item.||page2||index||||http://ep.yimg.com/ca/I/yhst-73691105158318_2111_796036||||ForKids||||||||||||||For The Kids!||||||||0||1||0||0||||xsooumcoso skate43 x250 ||||Electric scooters & MiniCycles for Tykes. (Wish we had these when WE were young. Kids today, I swear.)||||||||||||||||1||||Sports and Outdoors||||||New||||||||||||||0||~~|^^|gasscooters1||item.||page2||index||||http://ep.yimg.com/ca/I/yhst-73691105158318_2111_804544||||Gas Scooters||||||||||||||Gas Scooters||||||||0||1||0||0||||skate43 2006xg499 |||| Waaaahooooo...! (This is what it sounds like to ride our gas scooters)
These gas scooters are ready to rip, rock and roll! Guys and gals alike can't get enough of the power that comes with a small, swift gas scooter. They're durable and delightfully mean machines that easily handle rough terrain. Perfect on road or off, up hill or down these scooters are fast andfun!
||||||||http://store.thegostore.com/gasscooters1.html||||||||1||||Sports and Outdoors||||||New||||Gas Scooters||||||||||0||~~|^^|gogolfshirt||link.||||gostuff||http://ep.yimg.com/ca/I/yhst-73691105158318_2111_809350||||||GO! Golf Shirt||||gostuff > ||GOStuff > ||||||||||||||||0||0||0||0||||||Shirt, suitable for golfing or golf-related activities, such as watching others golf. Warning: On public courses, always wear WITH pants. (Learned that the hard way.)
Feeling weird? Wear a shirt with a big stupid traffic light on it!||||||||||||||||1||||Sports and Outdoors||||||New||||GOStuff||||||||||0||~~|^^|motorscooters||item.||page2||index||||http://ep.yimg.com/ca/I/yhst-73691105158318_2111_832182||||Motor Scooters|||||||||||||| Motor Scooters / Mopeds||||||||0||1||0||0||||cosoxbelmo xbelelmonoli xbelmosc ||||If these don't catch your eye, check your pulse. Seriously stunning machines, our motor scooters are our top sellers. Each model is unique with different sizes, styles and specifications. Take a little time to look at each--they're absolutely
NOTE: WE INCLUDE Residential AND lift gate delivery with ALL our mopeds/motor scooters! (It's part of the shipping cost, which we clearly show on every single scooter's webpage.)
Beware of online scooter or moped stores that sell you these mopeds at a cheaper price, claim "free" shipping, or simply hide the shipping cost until checkout-- make sure that residential and lift gate delivery are included in the cost! It is often $150 - $200 extra!
||||scooter, scooters, motor scooter, motor scooters, moped, motorcycle, mopeds, motorcycles, gas scooter, electric scooter, qingqi, lepton, metro sport, metro duo, vespa||||http://store.thegostore.com/motorscooters.html||||||||1||||Sports and Outdoors||||||New||||Motor Scooters||||||||||0||~~|^^|testitem||item.||page2||gostuff||http://ep.yimg.com/ca/I/yhst-73691105158318_2111_837230||||||One Dollar Pointless Donation||JW-MS-Dollar||gostuff > ||GOStuff > ||200.000||201.000 ||200.000 ||Donation Test||||0.000 ||||0||1||1||0||||||Donate $1.00 to The GO! Store for no good reason. (Don't click this.)||Ordering this item does ABSOLUTELY NOTHING except send us a $1.00 donation. Why is this even here? So we can test our ordering system! Why would you ever want to order this? You wouldn't, unless you're weird and want to give us a dollar for no apparent reason. (If you do? Um, thanks, I guess.)
The dashboard is an electronics chassis box with knobs for steering and balance feedback loop gain. This shows the early version of the dead man's switch, which really is not adequate. I found this out when I fell off, but the wire pulled apart instead of yanking out the connector. When it pulled apart, the exposed strands ended up touching to complete the circuit and keep it going. Fortunately, a safety feature in the software shut it down before it ran over my head. 
...all you have to do is make a little "hammock." Take a large drink coaster or other disk and drill three small holes near the rim, 120 degrees apart so they are equal distances apart. Run a string through the holes and tie together a foot or so (the distance depends on the size of your cup and the coaster diameter) above the center of the coaster. Support the hammock from the knot where the strings come together by hanging it on a hook or something. As long as the coaster doesn't bump into anything (it has to be able to swing freely) it is pretty hard to spill anything, regardless of how you move around the knot. You can even spin the thing in a big vertical circle so the cup is sometimes upside down, and nothing comes out. (Hopefully you won't do that with your scooter!) 
