Our team this year has switched from doing our usual omni wheel drive system and have decided to go with a 6 wheel drive.
We are using the 6" aluminum wheels from andymark with rubber belt as traction. We designed and built our own gearboxes that gear down the CIM motors 13:1 before being driven to the wheels. Our current set up uses one CIM motor per side. ( a total of 2 for the entire drive system)
When competing at waterloo this year we noticed that the drive would start to jitter and cut in and out when it was under the slightest bit of load. The controller was checked and the programmers are saying that it has nothing to do with the code. I am assuming that we are over loading the CIM motors and tripping the breakers … although it doesn’t seem right that they would draw so much current when they are not even under that much load. (just driving around the field and bumping other robots would cause the problem)
Can anyone give me some advice about what the problem could be ??
Our drivetrain uses two CIMs and six wheels as well.
We had similar problems in Portland. We never tripped a breaker but the robot was having trouble turning and the drive motors were getting flaming hot.
We solved the problem by removing the two front traction wheels (and the chains that drove them) and replacing them with omni wheels. Performance was GREATLY improved and the motors never over heated again.
Did you lower the center wheels of your robot? Most 6-wheel designs include a dropped center wheel to facilitate turning (the robot is never on more than 4 wheels and will turn on the center two).
Another no-brainer check is to make sure that you have 40A breakers and not 20 or 30A breakers pluged in line with the motors.
Also, make sure that your gearboxes are properly lubricated and that there is as little resisitance in them as possible. That’s all I can think of right now: Good luck!
If you’re robot is trying to brute turn a six wheel traction drive… you’re going to be killing your motors in no time!
With a six wheel drive, the common thing to do is to lower the central wheel by a tiny amount (1/8" for example) in order for the robot to turn with more ease. Other solutions involve switching some of the wheels to omnis or casters (the advantage of omni there is that you can power them to push forward and not completely lose the 6WD traction advantage). What I’ve also seen done is powered caster system that drops down every time the robot tries to turn.
If you have taken provision to make your robot turn easily, then it would seem to be an electrical problem (the “drive forward” code is straightforward enough that it is unlikely that there are any mistakes there). Recheck all PMW connections and make a continuity check with the frame to find a possible leak. As said, you should also make sure you have the right breakers in!
Try putting omnis on the “heavy” end of your robot. We found that with 6" IFI traction wheels on our six wheel drive “Aim High” bot, and two CIMs PER SIDE, that we had trouble turning even with lowered centre wheels. We put on a couple omnis, gave up a wee tiny bit of traction and gained a whole lot of mobility.
And Martin… you guys were only running one CIM per side? Wow. We couldn’t tell from watching in Portland. Guess a great machine doesn’t need a killer torquey drive train after all!
we have lowered our center center wheels by i beleive a 1/4" so the turning is very easy. We have made sure the backup battery is in and that there are 40amp breakers installed for the drive vistors.
In waterloo we replaced the traction material on the front and back wheels with strips of lexan to greatly reduce the friction. Although we are still having this problem.
Thank you for all your help and we will be sure to check all of our connections over this comming week in toronto.
Check your CIMs, I spent half an hour replacing one of ours because it was dragging down the whole drive (we have 6 wheel drive, 4 cims in total, middle wheel 1/8" lowered, and custom 12:1 gearboxes)
Maybe you didn’t, but lots of other teams did. Lots of people told us that we looked slow and wondered why we weren’t driving faster.
We are considering adding two of the FP motors to the drive for Atlanta to improve our acceleration. However, we will need to lose an additional 4 lbs. to make weight for this…
Bear,
A good place to look for trouble is to watch the voltage monitor on the OI during turns. If this voltage is repeatedly falling below 8 volts while turning, your drive is sucking huge amounts of current. Since you have replaced four wheels with lexan, you should not be having turning issues but it is possible that the lexan is still digging in when turning. Double check everything looking for lose wires, unclaibrated speed controllers and defective motors. I had one team report that they had one CIM motor that had developed an extreme difference between forward and reverse speed. Although I didn’t have a chance to closely examine the motor, I suspect that this motor was assembled without tightening the end cap screws. This allows the caps (and possibly the brush assembly) to move. Try moving the end cap with the wires and see if your motor caps rotate. They should not move. I don’t have a motor in front of me, but I seem to remember an alignment mark at each end. Make sure they are aligned and the screws are tight.