This instructable shows how to build my ArduRoller balance bot. It balances quite well on the spot and responds to most knocks pretty quickly but sometimes giving it a more gentle push sends it gliding across the room at a constant speed. I'm still working on that.
There's a video of the bot in action at http://www.flickr.com/photos/fasaxc/5944650602/.
There's a video of the bot in action at http://www.flickr.com/photos/fasaxc/5944650602/.
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Signing UpStep 1: Parts
Here are the parts I used:
1 x Arduino Uno
1 x Sparkfun Ardumoto motor driver shield
1 x Sparkfun BlueSmirf Bluetooth modem
1 x 150 degree/s gyro
1 x 1.7g Accelerometer
2 x Arduino header kits
2 x screw terminals
2 x 24:1 gear motor
1 x set of 70mm wheels
2 x JST connectors
2 x LiPo batteries
1 x basic LiPo charger
3 x Multi-turn 10k potentiometers
1 x SPST switch (Radioshack)
1 x Laser-cut bamboo chassis via Ponoko (link should allow you to make one from my shared design)
1 x LED
1 x Normally-open push switch
1 x packet of Sugru to make the bumber
Assorted M2-04 machine screws (6mm - 16mm) (found on Amazon)
M2-04 nuts to match machine screws above
Assorted straight and right-angle break-away headers
Assorted jumper wires
Solid core wire
Stranded core wire
Instamorph (aka Polymorph) low-melt-point thermoplastic
Notes:
Chassis: the motors didn't quite fit the mounts I made so I had to sand them down and rebuild them with instamorph. I think the sensor bundle suffers from too much vibration, it might have been better to make it more solid rather than sticking out as it does.
Accelerometer: I originally tried building the bot with only an accelerometer for tilt sensing and no gyro. It turns out that approach is a non-starter -- the accelerometer gets overwhelmed by the acceleration due to the motors so it can't be used to estimate tilt while the bot is accelerating. OTOH, using only a gyro would make the bot susceptible to drift over time so you really need both.
Gyro: I used a 150 degree/s rate gyro. From looking at the telemetry from my bot, I'm pretty sure it sometimes clip if you give the bot a knocks so if I was starting over I'd probably look for a 300 degree/s model.
Wheels: the wheels are a little fragile, after a few knocks I noticed cracks around the axle so I strengthened them with instamorph.
Motors: I also tried sparkfun's 100:1 gear motors but they weren't fast enough. The 24:1 versions have plenty of torque and speed.
Bluetooth: I use the bluetooth modem for telemetry right now but I'm also planning to use it for remote control from my Android phone. If you omit it then the robot will still work but tuning it will be harder.
Pots: I added 3 10k multi-turn pots to the design to allow me to easily tweak internal values. Using 3 might have been overkill since I tend to tweak only one thing at once.
Instamorph: Amazing stuff. It's a tough, white plastic (resembling solid nylon) at room temperature but if you heat it in boiling water it turns into a pliable goo that's really easy to work with your hands. A heat gun is great for working with it too, allowing you to melt small areas.
1 x Arduino Uno
1 x Sparkfun Ardumoto motor driver shield
1 x Sparkfun BlueSmirf Bluetooth modem
1 x 150 degree/s gyro
1 x 1.7g Accelerometer
2 x Arduino header kits
2 x screw terminals
2 x 24:1 gear motor
1 x set of 70mm wheels
2 x JST connectors
2 x LiPo batteries
1 x basic LiPo charger
3 x Multi-turn 10k potentiometers
1 x SPST switch (Radioshack)
1 x Laser-cut bamboo chassis via Ponoko (link should allow you to make one from my shared design)
1 x LED
1 x Normally-open push switch
1 x packet of Sugru to make the bumber
Assorted M2-04 machine screws (6mm - 16mm) (found on Amazon)
M2-04 nuts to match machine screws above
Assorted straight and right-angle break-away headers
Assorted jumper wires
Solid core wire
Stranded core wire
Instamorph (aka Polymorph) low-melt-point thermoplastic
Notes:
Chassis: the motors didn't quite fit the mounts I made so I had to sand them down and rebuild them with instamorph. I think the sensor bundle suffers from too much vibration, it might have been better to make it more solid rather than sticking out as it does.
Accelerometer: I originally tried building the bot with only an accelerometer for tilt sensing and no gyro. It turns out that approach is a non-starter -- the accelerometer gets overwhelmed by the acceleration due to the motors so it can't be used to estimate tilt while the bot is accelerating. OTOH, using only a gyro would make the bot susceptible to drift over time so you really need both.
Gyro: I used a 150 degree/s rate gyro. From looking at the telemetry from my bot, I'm pretty sure it sometimes clip if you give the bot a knocks so if I was starting over I'd probably look for a 300 degree/s model.
Wheels: the wheels are a little fragile, after a few knocks I noticed cracks around the axle so I strengthened them with instamorph.
Motors: I also tried sparkfun's 100:1 gear motors but they weren't fast enough. The 24:1 versions have plenty of torque and speed.
Bluetooth: I use the bluetooth modem for telemetry right now but I'm also planning to use it for remote control from my Android phone. If you omit it then the robot will still work but tuning it will be harder.
Pots: I added 3 10k multi-turn pots to the design to allow me to easily tweak internal values. Using 3 might have been overkill since I tend to tweak only one thing at once.
Instamorph: Amazing stuff. It's a tough, white plastic (resembling solid nylon) at room temperature but if you heat it in boiling water it turns into a pliable goo that's really easy to work with your hands. A heat gun is great for working with it too, allowing you to melt small areas.
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The other values are the calibration values for my particular sensors. You'll need to work those out for your own sensors too or experiment until you find the right values.
Using the shaft encoders would help oscillation because I could reduce the integral term and rely instead more on the shaft encoders. Unfortunately, amalgamating multiple inputs like that requires more complex control algorithms that I'm not familiar with.
Low pass filter the accelerometer with a very low corner (comparable to the drift time of the gyro). Add that into your angle calculation, rather than directly adding it in. I don't think you need a Kalman filter. That is for noisy signals. (Yes the accelerometer is "noisy", but not in the band of interest). Put optical encoders on the motors and feed this into the loop. This will stop "running across the room". (The reason Segway doesn't need this is the rider controls this).
Put weight up as high as you can get on the bot. That will increase the stability.
It's definitely not a cheap bot if you go with all the parts I used. I'd guess that I spent about $300 on it plus I had to buy tools. There are some parts that aren't necessary (like the $50 Bluetooth modem) and there are certainly cheaper motors and batteries available (you could probably save $50 there). I didn't work too hard to reduce the cost because I was building it gradually over a couple of months and I've found in the past that it's too easy to spend 5 hours searching only to save $5.
I'd say it's a medium-difficulty project. The physical build isn't that hard (although cramming everything on the protoboard is a bit fiddly) but tuning it to stand up correctly took me a long time with a lot of trial-and-error.
Do you do custom laser cutting? What're your shipping times/rates to California like?
They are modifiable from 224:1 to 14:1 by removing a gear and are far more robust, plus... they mount ROCK SOLID with through hole mounting and the wheels that they use are nylon, inexpensive, and unbreakable.
Again, very nice bot!