Help with IQ Smart Motor internal gears clicking/slipping

Looking for some guidance on a smart motor issue. We have a team whose robot is big and geared up to go fast, but the stress being put on the two drive-train smart motors when stopping/starting suddenly is causing the internal gears to slip/click. Has anyone else experienced this and solved it, aside from reducing the gearing and slowing the robot down? Maybe through programmed acceleration/deceleration, adding motors to the drive-train to distribute the stress, or some other kind of mechanical adjustment that simulates braking or otherwise eases the momentum force being applied to the gears when going from forward to reverse, or vice versa, suddenly? Just looking for a general direction for the team members to explore before they turn the motors into $20 paperweights.

Have you adjusted the speed and torque of the motors through programming?

They don’t want to reduce the overall speed through programming, because they want it to go fast. Perhaps there is a way to program it in a way that simulates braking when changing motor directions? So that the motors don’t go from 100% forward to 100% reverse, but rather some kind of gradual slowdown, even if it’s just milliseconds. I’m guessing it’s possible but am curious if anyone has ever tried it to solve this problem.

They have been able to reduce/eliminate the slippage by manually being more gradual on the joysticks, but that takes a lot of concentration, and they’d rather not have to think about it in the heat of a timed match.

You can definitely limit acceleration. Some of my teams have done it to improve accuracy but we’ve never experienced internal gear slippage so we’ve not done it to solve that particular problem.

There are several ways to do it. You can create a function to ramp up power based on measured time, or just save the previous power value and limit the next value to some small delta from that before inputting into the drive command.

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Our programmers are meeting tonight so I’ll ask them to investigate something along those lines. They could benefit from improved accuracy anyway.

Hi Robokai did you ever solve this issue?
One of my teams has the exact same issue with geared up drivetrain and the internal gears are slipping and then stopping altogether.

provide more details pls
what rpm? what wheel diameter? how many motors? stuff like that

Wheel Diameter - 210mm
2 Motors at the rear (with chain to the front)
Velocity set to 100%
IMG_2657 IMG_2658 IMG_2659

Thanks in advance.

Looks pretty standard setup. You have both ends of the axles supported and the chain doesn’t look overly tight.

What’s the drive ratio off the motor to that 12tooth gear that’s driving the wheel? (Picture 1)

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i need the rpm. the percentage of the velocity or number of motors doesn’t rly help lol

the ratio as foster said is important for us to know because we’ve gotta see if you are having torque problems, or if it’s some other issue

Sorry guys and thanks for your help.

The gear ratio is 5:1

In the code the team hasn’t set RPM, but when testing RPM via the brain (and not under load) the RPM of the left motor is 87mph and right motor is 92mph.

Thanks Ethan. The robot is reasonably heavy and when it is not under load (on its side) the drivetrain is extremely fast.

So your problem is:
Your 5:1 (speed) drivetrain is causing the motor’s internal gears to slip/stop? Which one does it do, slip or stop?

if you can send a vid it may help. i’m not awfully familiar with vex iq stuff, but i think its reasonable to assume that the forces at play work similar to edr

and yeah this is a good question that would be helpful to know the answer to as well



Here is a short video showing the issue. I may not be explaining it properly, but as you c an see in the video the robot is slow with the gears slipping and then won’t turn.

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Hmmm, that’s an interesting problem. One time I tried doing a 5:1 drive and it just didn’t move. I’m guessing your bot has just enough weight to let the drive move it, but just not enough to keep it going? I would recommend trying a smaller gear ratio to give more torque (perhaps 3:1). Use the same motors to find out if it’s a problem with the motors.

two things you can do to potentially fix this- first is the most sure-fire way (assuming it’s not the motors themselves causing a problem) and includes simply changing the ratio to something that provides more torque as noah said.

the second option im about to mention may or may not work (depending on some variables in iq im not totally familiar with) but you can try it if you feel that you absolutely need that ratio for whatever reason-
you can try distributing the power differently; instead of focusing it all through that one small 12t gear, you can try adding another gear train of the same ratio somewhere else on the drive to share the power (maybe at the other wheel, or something like that. just make sure both wheels are going the same speed lol). a problem with this is that it will undoubtedly increase friction, although this could probably be made negligible. i did something similar to this last year with my 300 rpm 4” drive in vrc and while it took some tuning it worked pretty damn well

(the reason why this second solution may [or may not] work is because it seems to me that the poor plastic 12t gear in your drivetrain simply can’t handle all the stresses of accelerating to the speed you want. it may be bending, experiencing micro warping, or leading to something similar in the shaft, but either way it’s pretty clear something in that design isn’t holding up to the 2m worth of power going through that little gear. if you arent already, you can also try using a metal shaft just to see if that changes anything)