Gyro Autobalancing

[jutayo23]

Team 1124 has gotten autonomous bridge balancing to work very well. Here's a video of our previous year's robot with the balancing code on it (this was before this year's robot was completed) You'll notice the bridge in this video is easily tipped. Our bridge was too light, which made balancing harder to achieve. The code worked even better when we tried it with a competition bridge.

http://www.youtube.com/watch?v=z2RpnQAU1dY

If anyone's interested in our method:

We use both a gyro and accelerometer to balance our robot. The gyro is good at giving an accurate angular rate, but not absolute angle, while the accelerometer is good at giving an accurate absolute angle, but not angular rate. We decided to combine the best features of both these sensors to get the best control.

I don't want to release the entire code yet, but here's essentially how it works.
It uses a state machine to decide how to behave. The driver drives the robot slowly up the bridge until the gyro rate is greater than a certain amount in either direction, at which point the code takes control of driving. The robot then drives in the opposite direction until a second significant angular rate is detected. After this sequence, the accelerometer is read for an accurate angle reading. If it is determined that balancing failed, it restarts. If it determines it is balanced, it holds its position and waits for the gyro to return a significant rate allowing it to re-balance.
You should be able to see all of these steps from the video above.

We use closed loop control on the drive (with PID) to control the rate at which the robot drives up the ramp in order to keep consistency.

Our drivers have been very pleased with this feature. It has yet to fail. It almost always balances the robot on the first try. When it doesn't, it gets it on its second, as seen in the video. This method is much faster than when our drivers attempted it manually.

I'd be happy to answer any questions related to our method of balancing, PID, or the sensors we used. Good luck to anyone else attempting this!