[archiver]

Posted by Ken Leung at 1/31/2001 10:59 PM EST


Student on team #192, Gunn Robotics Team, from Henry M. Gunn Senior High School.


In Reply to: Controlling Arm travel - Limit Switch or Mechanical Stop?
Posted by Peter Zobel on 1/31/2001 3:06 PM EST:



: Rookie team requesting advice...
: What is the best way to limit travel of an arm - limit switch? Mechanical stop? Both? Neither?

Last year, we had a giant arm (yes... again...), and we use it to reach up to the hanging bar and pull ourselves up. Since we used the Van door motors to power that arm, along with the fact that Van door motors back drive under large amount of force, we had to come up with a mechanical lock. And basically, there is this spring-loaded flap that will hook onto the body structure once the body is raised close enough.

So why did I tell you this? Well, it's because while designing this arm, a concern about accidents was raised up. What if the arm moves too fast and locks into the body during a match? The driver might accidentally push the arm too close (well I was the driver and that never happened :-) ), or some other robot might accidentally (or intentionally) lock our arm in. And we concluded that due to the nature of "accidents", a limit switch might not be quick enough to prevent the locking, or the outside force might be too great for the Van door motors to push against.

So we ended up making a little door on the structure to prevent the flap from sticking into the structure, and everyone was happy. The little door works perfectly and the arm never ever lock in when we didn't want it to. We probably should've attach a limit switch so our arm won't keep crashing into the door all the time, but I had enough practice to keep the arm just a little bit away from the body.

So I guess another important thing about this issue is that you want your drivers be trained to not destroy your robot, and good enough to take care of it.