Another CIM Question

Well guys, this is MOE’s second year using the CIM motors as our main powerplant. Unfortunately this year we have encountered a slight dilemma.

With a multi-speed transmission, we’re having a slight problem moving our robot. Unless it is in its lowest gear, (Approximately a 15:1), the robot will not move. Our second gear is a 5:1 ratio, and will not move the robot one bit.

Our wheels are approximately 2.5 inches in diameter. It’s bothering me to no end that this robot will not run in this gear.

I’ve checked the drivetrain numerous times for any type of binding, but alas I’m still stuck.

Any help or suggestions with how your robots are managing to run?

Thanks guys, (And girls).

It may be that the motor does not have enough starting torque to get the robot moving in high gear. If this is true, you are probably overloading the circuit breaker, and it is popping., This will certainly result in the robot not moving.

Try lifting the robot off the ground and trying it.
If this works, then you may need to start off in first gear, then shift to second once you get going.

Explain the problem a bit more for us in order to help you Carlo…

Whats happening to the wheel? How are you powering the wheel from the output of the transmission (sprockets, chains)? Are all the wheels touching the ground?

<edit> Please try what jskene pointed out first. <edit>

I find that strange also. Last year through a snafu, we managed to get a fixed 4:1 ratio to our wheel on our bot, and we were using the large skyway pneumaic tires. The bot ran decent too, just heated the the motors really quickly. But, we did only have an 85 pound robot so your results may vary. What kind of drivetrain are you using? We were using mid-wheel 2wd design with castors in each corner. I would think that with only 2.5" dia wheels, 1:5 should move your bot.

Sorry I wasn’t more specific guys… I was crunched on time.

So a better explanation.

Dual motor drive using the “Nothing But Dewalts” transmission setup. Big thanks goes out to Joe and Joe.

The motors are set up so that both will spin in the same direction (Not one in reverse) and linked to our ouput shafts with sprockets and #25 chain. Beings the gearing on the Dewalt transmissions are 12:1, 4:1, and 3:1, we have the additional 5:4 gearing in our sprockets.

The 2.5 inch wheel accounts for our main wheel turning our treads. The problem happens in a straightline, not just turning, so I know it’s not a tread dilemma.

It does spin just fine in any gear while up in the air, but with the specs on the CIM motor, it doesn’t make sense to me why it wouldn’t work on the ground. At approximately 110 lbs this year, we should have no problem, as the torque works out to be higher than our 130 lb robot last year. Unless the Dewalt gearbox’s efficiency is under 70% that is.

I imagine the problem is the spike when starting them, but I’ve got amp meters hooked up and they’ve pulled 37 at the most.