Self-Balancing 2 Wheeled Robot

[Mike]

Since build/official competitions are over I've been working on making my own robot. Currently, the frame is done (I'll try to post pictures later, for a CAD model see bottom of the post) and I'm looking at what electronic parts I should buy. Here's my current list:

Microcontroller $85.95

6 AA Battery Holder $0.75

Solarbotics GM8 Gearmotor (2x) $12.00
Solarbotics Plastic Wheel (2x) $8.00
Shipping: $4.95

12" PWM Cables (2x) $18.94


What I need is a gyroscope, although of all the researching I've done of balancing robots people have used both gyroscopes and accelerometers. Will just a gyroscope be sufficient? Does anyone know a good/cheap gyroscope/accelerometer that I would need?

Thanks in advance.

CAD Model:
*Note: Those aren't the motors I'm using, and it's wood... not metal.*



EDIT: Whoops, this was supposed to go in Technical Discussion, any mod feel free to move it.

[colt527]

Hmm, I think this is a quite a task to take on, You are basically reproducing a segway and Im pretty sure Human Like movement based on balance is not an easy thing to pull off both programming-wize and mechanical wize. Its going to take a lot of effort to pull it off.

On the hardware side:

Ive seen balancing done with distance sensors as well though. Where they point at the ground and measure the distance difference between the 2 sides and make movement decisions based on that. And, I dont know much about the speed of the microcontroller that you need to accomplish this feat but I imagine that it needs to be pretty fast and update often.

Sorry I couldnt be more help, but good luck! and I hope to see it working

[sanddrag]

I once tried my hand at a fullsize one with a Parallax BS2 and a Memsic Accelerometer (that parallax sells) but never really got too far with it. I'm not a programmer but even I I was, I'm not sure if the electronics and hardware are capable of balancing.

You may find some useful info at www.tlb.org

[artdutra04]

Originally Posted by colt527

Hmm, I think this is a quite a task to take on, You are basically reproducing a segway and Im pretty sure Human Like movement based on balance is not an easy thing to pull off both programming-wize and mechanical wize. Its going to take a lot of effort to pull it off.

Let's not forget that Mike was the one who coded a working autonomous code that used the camera and capped the vision tetra.

I think you may find this site very informative:
http://www.geology.smu.edu/~dpa-www/robo/nbot/

Also, people have built a "Legway" balancing robot using Lego Mindstorms:
http://www.generation5.org/content/2004/legway.asp

[Paul H]

I've got a gyro you can have, I got a few from the yardsale last year and I only really need one. It's the gyro that was in the kit from previous years. All I ask is that you pay shipping.

[Kevin Watson]

Originally Posted by MikeWasHere05

What I need is a gyroscope, although of all the researching I've done of balancing robots people have used both gyroscopes and accelerometers. Will just a gyroscope be sufficient? Does anyone know a good/cheap gyroscope/accelerometer that I would need?

This is the classic inverted pendulum problem that is given to countless college students each year. You'll need to implement a Kalman filter that'll filter noise, perform sensor fusion and spit out a state estimation. As you've already found out, you'll need a gyro and an accelerometer that's sensitive down to zero Hertz (i.e., gravity). Sparkfun has a gyro/accelerometer board that looks good. The part number is ACL-IMU-203.

-Kevin

[Mike]

Wow, didn't realize it'd be this expensive/complicated.

I'm gonna think about maybe a lower cost/simpler alternative to a gyro, maybe a feeler attached to a pot? If you have any suggestions feel free to post =)

EDIT: Or anyone know how I can build something similar to http://www.sparkfun.com/shop/index.p...s=ACL-IMU-203& for cheaper?

[BrianBSL]

Originally Posted by MikeWasHere05

Wow, didn't realize it'd be this expensive/complicated.

I'm gonna think about maybe a lower cost/simpler alternative to a gyro, maybe a feeler attached to a pot? If you have any suggestions feel free to post =)

EDIT: Or anyone know how I can build something similar to http://www.sparkfun.com/shop/index.p...s=ACL-IMU-203& for cheaper?

The sparkfun IMU is neat in that it is all on one board, but you can get evaluation board versions of the same things from Analog Devices (www.analog.com). You can probably save $30-$50 by buying separate EB's instead, but you aren't going to get comparable performance for much less. Make sure you buy EB's or something with the devices mounted. The gyro's are all ballgrid and aren't worth the trouble of mounting yourself, you can solder the accelerometers as they are a small surface mount pitch but its still easier to buy EB's that have all the resistors and caps installed that you need.

As far as something simplier/cheaper, I've seen people attempt the same design using two IR distance sensors on each side.

[Mike]

Originally Posted by BrianBSL

As far as something simplier/cheaper, I've seen people attempt the same design using two IR distance sensors on each side.

I've decided to use a potentiometer connected to a "feeler" to sense the angle that the bot is at. Once I get that working, I'll buy some IR sensors and use those.

[seanwitte]

Originally Posted by MikeWasHere05

I've decided to use a potentiometer connected to a "feeler" to sense the angle that the bot is at. Once I get that working, I'll buy some IR sensors and use those.

You could use the pot as the pivot point for a small pendulum mounted inside the frame. It might have to be heavy to overcome the static friction of the pot, but it would be doable. The value of the pot would be proportional to the tilt angle.

[Mike]

Originally Posted by seanwitte

You could use the pot as the pivot point for a small pendulum mounted inside the frame. It might have to be heavy to overcome the static friction of the pot, but it would be doable. The value of the pot would be proportional to the tilt angle.

Good idea, probably will try it after the feeler idea. Right now I'm kinda limited to my space/weight, but I'll be sure to check it out later.

[Alan Anderson]

Originally Posted by MikeWasHere05

I've decided to use a potentiometer connected to a "feeler" to sense the angle that the bot is at. Once I get that working, I'll buy some IR sensors and use those.

A feeler will work as long as the surface is flat and level. Without a true sense of "down", a Segway clone will want to accelerate downhill.

[Mike]

Originally Posted by Alan Anderson

A feeler will work as long as the surface is flat and level. Without a true sense of "down", a Segway clone will want to accelerate downhill.

Yeah, I was thinking about that. So I might make a feeler design just to experience with using a pot as an angle measurement.

There's also a problem with the pendulum idea. If I am making constant adjustments to control the angle, then the pendulum will start swinging. The swinging will cause harder adjustments, which will just feed this repetition harder until the robot tips. I'm thinking of something along the classic pendulum lines, I'll try to make up a CAD drawing and post it later.

[Alan Anderson]

Originally Posted by MikeWasHere05

There's also a problem with the pendulum idea. If I am making constant adjustments to control the angle, then the pendulum will start swinging...

If you mount the pendulum to hang from the point of rotation of the platform (i.e. the axle), you'll have a lot less to worry about. You can account for the approximately known linear acceleration and compute something very close to the actual tilt. Modeling the dynamics of the pendulum might still be necessary, but you won't have to deal with the chaotic "double pendulum" system that would arise if the pivot point were somewhere above the axle.

[Mike]

Originally Posted by Alan Anderson

If you mount the pendulum to hang from the point of rotation of the platform (i.e. the axle), you'll have a lot less to worry about. You can account for the approximately known linear acceleration and compute something very close to the actual tilt. Modeling the dynamics of the pendulum might still be necessary, but you won't have to deal with the chaotic "double pendulum" system that would arise if the pivot point were somewhere above the axle.

I can see how that would stop the pendulum from swinging wildly, but for the pot to take readings, it has to be mounted on the pot, right?

The way I'm thinking of designing a pendulum is for it to be less of a circular motion of swinging and more of a linear one. Think of a box with beads in it, when it's tilted the beads fall to one end of the box instead of swinging like a classic pendulum would. Of course, I wouldn't use beads.