Drill Motor Output - Fwd vs Rev

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Posted by Nate Smith.

Other on team #66, GM Powertrain/Willow Run HS, from Eastern Michigan University and GM Powertrain.

Posted on 1/31/2000 8:24 AM MST



Just thought I'd throw this out there and see if anybody knew the answer before I went to the trouble of figuring it out myself...I'm working on adjusting the drive train of our machine(using the drill motors), so that the differences in the speeds of the motors between forward and reverse are 'scaled out' by the program. I was wondering if anybody had the numbers for roughly what the difference was, so I can incorporate the scaling into my program without taking a lot of time to figure out the differences...I had it close once, but then we found out we were getting extra friction on one motor, so now I'm not even close any more...please, help!

Thanks!

Nate

[archiver]

Posted by Jerry Eckert.

Engineer from Looking for a team in Raleigh, NC sponsored by .

Posted on 1/31/2000 10:32 AM MST


In Reply to: Drill Motor Output - Fwd vs Rev posted by Nate Smith on 1/31/2000 8:24 AM MST:



: Just thought I'd throw this out there and see if anybody knew the answer before I went to the trouble of figuring it out myself...I'm working on adjusting the drive train of our machine(using the drill motors), so that the differences in the speeds of the motors between forward and reverse are 'scaled out' by the program. I was wondering if anybody had the numbers for roughly what the difference was, so I can incorporate the scaling into my program without taking a lot of time to figure out the differences...I had it close once, but then we found out we were getting extra friction on one motor, so now I'm not even close any more...please, help!

: Thanks!


My advice is not to worry about it. I worked on the control system for four years
and never compensated for the forward/reverse difference in the drive motors and
our drivers never had a problem (which is what really counts). While there may be
a difference in the characteristics of a given motor operating in forward vs. reverse,
there are also differences between different motors, mechanical assemblies in the
robot, friction with the flooring, etc. The temperature of a motor will also affect its
operating characteristics.

Even if you were to achieve a perfect balance, you'd have to repeat the entire
procedure any time a component in the drive train is replaced or adjusted.
Your drivers can learn to compensate much faster than you can do so in the
control program.

Two things I have observed:

(1) The motors operating in reverse tend to run hotter. Because of this, we'd try
to swap the motors from side to side whenever we had to remove them, especially
during practice when they were run for extended periods.

(2) The one time there was a noticable difference between motors from the driver's
perspective was when trying to creep forward from a stop; however, this seemed to
be affected more by the variance between different motors than by whether a motor
was operating in forward or reverse. We reduced this effect by programming a dead
zone into the joystick (i.e., if the stick input was 127 +/- n (I think I used n=10) th
input value was set to 127).

Jerry