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#4
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Use both
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. |
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