[archiver]

Posted by Joe Johnson at 03/21/2001 10:44 AM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: this question appears over and over again
Posted by Ken Leung on 03/20/2001 10:02 PM EST:



I really recommend that you think hard before implementing a cure that is likely worse than the illness.

Unless you are very careful, bevel gears will be a constant source of problems for you.

It is not that hard to fix it in software if you like.

With advanced planning, it is not that hard to make your motors rotate in the same direction.

Finally, it is also not that hard (imho) to train your drivers to drive through it.

All of these solutions beat bevel gears and (horrors!) worm gears by a long shot.

Joe J.

P.S. Code below will give more gas to the wheel running in reverse.


PWMLeft is left wheel output
(assume fwd robot motion runs motor in reverse)
PWMRight is right wheel output
(assume fwd robot motion runs motor is forward)


BOOST_NUM CON 140
LOG2_BOOST_DEN CON 7
'Effective boost = BOOST_NUM / 2^LOG2_BOOST_DEN

'in the above case boost= 140 / 128 = 1.09

'use whatever means you normally use to generate the

'PWM outputs for the left and right wheels then use the

'following code to modify these values


if PWMLeft > LOG2_BOOST_DEN + $80 MAX $FE
NoBoostLeft:
if PWMRight > $80 then NoBoostRight
PWMLeft = $8080 - ($80 - PWMLeft * BOOST_NUM >> LOG2_BOOST_DEN) MIN $8000 - $8000
NoBoostRight:

The above code assumes 128 is "off" (128 = $80) for both wheels, this is the standard Victor calibration.

Good Luck.

P.P.S. I have seen the charts from the motor mfg (they are too bad of a fax to post) in both directions. According the these charts, the performance difference is only a few percentage points. Yet, Folks I know and love swear by the fact they see real control problems due to motor rotation directions. So... I differ to their knowledge born of experience. I offer the (untested) code above off the top of my head in the spirit of gracious professionalism. Let me know if it does not work. I am pretty confident that it is right but I am human so it may not be 100% correct.