Re: Implementing Traction Control for an advantage in the 2009 game
 

Daniel is wise, you should pay attention to him.

Eugene

Re: Implementing Traction Control for an advantage in the 2009 game
 

Doug-- Because of the weird resonances between the pwm outs and the motor kick-back, the amperage ranges wildly as you accelerate and decelerate, making it tricky to determine slip. You could potentially compare the values to a baseline, and if it's higher or lower adjust the pwm output.(baseline determined in conjunction with accelerometer...?)

Re: Implementing Traction Control for an advantage in the 2009 game
 

That is why I think it would be difficult at best. We use an undriven wheel with an encoder to test agaisnt the speed of the driven wheel.

I would like to hear about someone who had used tracking current and how it worked or didn't work.

Re: Implementing Traction Control for an advantage in the 2009 game
 

So, you guys appear to have validated the following file attachments obtained from some of my colleagues who are presently enrolled in an Hybrid-Electric vehicle class at UofM-Dearborn.

Re: Implementing Traction Control for an advantage in the 2009 game
 

I love it when science works right!

Re: Implementing Traction Control for an advantage in the 2009 game
 

What is surprises me is that the difference between asphalt, wet asphalt and regolith is about the same for the slippage factor and traction. You would think it would be a greater difference between surfaces.

Re: Implementing Traction Control for an advantage in the 2009 game
 

If you could accurately measure average motor current, and therefore motor torque, given the typical longitudinal traction curve shown in the plot posted earlier, just what would you be inspired to do?

Eugene

Re: Implementing Traction Control for an advantage in the 2009 game
 

Correct me if I'm wrong, but I believe that this works:
I'd make a table of a few test values, finding the current draw at various pwm outputs with no slip, and then have my program look for a result that was more than twenty percent less current draw than the values in the table. Since speed and current are inversely proportional this should mean that the motor is spinning more than 20% faster than normal loaded speeds-- hence spinning out. I'd then have it decrease the wheel speed(move the pwm output towards neutral), and then check the wheel for slip again, adjusting as necessary until 20% slip was achieved. Sort of a recursive algorithm.
Basically, since the current draw means nothing by itself, test values must be taken. They probably even vary from motor to motor.
And as for decelerating.... I think that has to be a joystick filter thing. Not much you can do with currents alone.


By the way Eugene, thanks for the current sensor tip. I'm still checking the legality of my method, but it looks like the output from those ICs will even work with the program we have(just new test values). :]

Re: Implementing Traction Control for an advantage in the 2009 game
 

Don't you just want to maximize torque and let the wheel slip
take care of itself? Imagine your self somewhere on the x axis
of the first curve and adjust the motor PWM drive (which will
adjust the slip) in the direction of increasing average current.
Where do you end up?

In the case that you want a specific torque that is less than
the maximum there are two spots on the curve and you might
prefer the one on the left.

Why is the situation any different when braking, as long
as the current is going through the current sensor?

Don't forget to install a suitable RC filter on the output of the
current sensor. For Jaguars with their very high chop rate
it might not matter. For the Victors that chop at 120 hz it will
matter...

Eugene