Posted by Dodd Stacy.
Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.
Posted on 2/15/2000 7:51 AM MST
In Reply to: Clearifications on our 'bot posted by nuts4first on 2/15/2000 7:04 AM MST:
: Our drive system is like this…
: 4 wheel drive, using 3/8’ chain to power a forward and aft 6’ wheel. The drill is in the center powering a 15 tooth sprocket with two loops of chain going to each of the wheels. The sprockets on the wheels are 18 teeth. We have set the drill gear box to drive in low gear all the time.
IMHO, you are NOT over-geared. I make your top speed around 6 ft/sec or slightly less, and that gearing should be ok, in terms of the current you draw in accelerating.
In terms of friction, binding, etc in your drive line, exercise extreme care when adding constraints like extra pillow blocks to align them so they don’t fight each other. It’s easy to cause more problems than you solve. You might try blocking your bot off the floor and running the drive lines as you loosen the various mounts for the shaft bearings and the motors. (Careful with fingers!) Listen for changes in speed as you relax the positional constraints. More importantly, follow this procedure as you snug, then tighten the mounting constraints back up. Maybe run your chains a tiny bit looser than you otherwise think you should.
Then go back to your original diagnosis. How hot is hot? What is very hot to the touch may be quite comfortable for the motor. Yes, the efficiency and power output suffer as the temp rises, but I think you’re worried about damage rather than performance. I gather your motors are exposed, so you can touch the housings? If so, you might periodically cool them during practise. Joe suggests the canned freon stuff. A very slightly damp (with water) sponge or rag on the housing is also good, as long as the water evaporates rather than runs in and shorts out your motor.
We don’t have much direct experience with how hot these motors run during ‘normal’ use in drilling/screwing. This is a great area for a FIRST ‘White Paper’ science project. Why don’t we DO this some time? Good luck, nuts. Let’s hear how you make out.