Implementing Traction Control for an advantage in the 2009 game

[Paul Copioli]

EricS,

We tried the joystick method and it works great. It was very simple to implement and we just wanted to see if it made a difference ... it does big time (as we expected)!

I do not think this is the best way as it does not actually account for actual wheel speed. Caution: this post might get a little long.

First, a description of what we did. We forced the maximum PWM input change from the joystick from one time step to another to be a certain value (ours ranged from 1 to 10). We only had it working in the forward direction as we had a bug that made it not working in reverse (we were trying to do it fast).

When diving around on the actual surface with the actual trailer and wheels with the trailer loaded (about 40 - 45 lbs) here is what we found:

The "poor man's traction control" worked great except when you tried to turn the trailer and it took longer than the ramp up. The wheels would eventually break free and spin but backing off on the throttle would bring it back down and gain traction. I think people will be suprised when they see how much trailer weight affects turning performance. Anyway, it proved to us that traction control is a must.

In my mind there are 3 basic ways to do traction control this year:

1. Poor man's - as described above just control throttle rate.

2. Middle Income - Encoders on the driving wheels only. Control the rate of change of wheel speed (also known as acceleration) to match what the surface can handle.

3. The super rich - Do the same as number 2, but add a frame of reference like a non powered wheel or an accelerometer. In addition to controlling the change, you also make sure the wheel speed is close to the frame of reference speed.

Our team is leaning towards #2 and here is why:

1. As I proved in a different thread, the maximum acceleration we can have is equal to g*CoF, where g is the acceleration due to gravity and CoF is the coefficient of friction between the floor and the wheels.

2. Since this is a known quantity we can set the maximum wheel speed change per time step based on testing.

3. In addition, we can cap the maximum speed (if you think that is important.


If this proves to not be enough, then we will probably use an accelerometer as a reference.