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Posted by Mike Gray.

Engineer on team HOT from Huron Valley Schools sponsored by GM Milford Proving Ground.

Posted on 3/2/2000 8:29 AM MST


In Reply to: control system programming posted by Jimmy Holmes on 3/2/2000 6:26 AM MST:



Suggestions:

1. Eliminate the possibility of mechanical problems, with the motor or with the drivetrain.
2. Check for volt drops across terminations.
3. Check the integrity of the suspect speed controller, per InnovationFIRST instructions.
4. If the first three are fruitless, scale the PWM value to the speed controller:

First, determine the speed error. Declare a new variable which will be scaled to reflect the speed error. The new variable will be a transfer function for the faster motor. Perform a slope and intercept (mX+b) transform on the joystick variable and set the new variable equal to it.

Example:

new_variable=joystick / 2 + 64

This example assumes that you want to scale the variable to half-scale. You must add 64 counts so that 127 counts still represents center-stick. If you want 1/4 speed, simply divide by 4 and add 96.

Unfortunately, this method wil not make full use of the faster motor's potential, but you can't make the slow motor go any faster than 255 counts.

Even after scaling, the motors may launch unevenly due to variation in static friction. If you need to start the motors many times during a match, static friction may cause the linkage to 'warp'. I suggest using the x-axis on that joystick to modify the y-axis variables, so the operator can make small corrections to the linkage on the fly.

Hope this helps.