[archiver]

Posted by Joe Johnson at 1/31/2001 6:54 PM EST


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


In Reply to: Mechanical stop good
Posted by control guy on 1/31/2001 5:34 PM EST:



Good, solid, mechanical stops are a must. BUT Limits
switches and pots will save you a lot of headaches.

Basically, running full throttle into a hard stop puts
extremely high stresses on the internal mechanism of
you motors as well as on your robot itself.

Even if your robot can survive, many of the motors
cannot. In particular, the Bosch motor can only take a
dozen or so such hard stops before the output of the
motor is severely limit. The Fisher Price
transmissions are not too happy with hard stops either.

One more reason to put in a limit switch or a pot is
that the motors stall against a hard stop. In the heat
of the battle, an excited driver may stall several
motors against their stops. I know of several teams
that popped their 60 amp fuse because an arm driver
stalled the arm motor against the stop during a pushing
match -- ouch!

As to the high speed motions blowing by the electical
limits, one strategy
to deal with this is to have the switch make early
enough to stop the motor then go to a "low power" mode
(via programming) that will allow the motors to be
driven to the end of travel but won't draw too much
current. You may want to have even this low power mode
time out -- i.e. have it go to zero as time passes.

Good luck.

Joe J.