Robot running slower

Hi all,

Why would a robot get slower over the time? My team’s robot seems to be running slower than before. Not sure why and what would be the possible solutions.

Thanks in advance for your help.

Try changing the motors, changing the axles, and changing the gears

When you say it slows down over time, do you mean it runs perfectly at the start but slows down after a few minutes (in which case it means your motors are over heating) or do you mean that ever since you started driving it, it has been getting slower and slower (over a course of for say days or weeks)?

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I would say both. We feel like it has been getting a slower and slower. Also, today we realized that motors are over heating.

It could be a ,burnt out motor, broken battery, or dirty wheels.

You may want to check that you have washers or spacers in between all the places that plastic would otherwise rub together. Missing washers leads to lots of friction, which means motors have to pull more power to keep moving the robot.

Additionally, if your axels are cantilevered (not well-supported in enough places to support the weight of the robot on the wheels), that can cause significant friction and rubbing against the plastic holes, which will shave off plastic, generating even more friction.

Edited to add: if you have some pictures of the robot, lots here will be happy to point out places to look to for most likely issues.


Here are some photos of the drivetrain.

These pictures do show a lot of dust. Like others have said before, there may be excess friction in the system caused by dust build up?

Again restating from above, another possibility could be that the holes that used to act as a perfectly round bearing surface spaced ever so perfectly far apart are no longer perfectly spaced or perfectly round. That dust means material was removed from somewhere and my guess is that it came from the axles making the holes oblong. When this happens, things can fall out of that perfectly spaced distance and cause extra friction because the gears are no longer meshing perfectly.

I know this thread hasn’t been completely helpful in actually diagnosing what is wrong with your robot, but it seems that most of the most likely suspects have been identified.


The pictures definitely help. Looking at the drivetrain gears, there are definitely not washers on both sides of the gears. In the first picture you can even see where the gears are not lined up the same way across the gear box. Washers should be on both side of the gears.

Additionally, I’m going to hazard a guess that there are no washers between the rubber collars and the plastic, which will cause a LOT of friction.

Start with addressing those items (and blow out what dust you can when you’re rebuilding the gear box) and see if it starts to address the issue.


Do what everyone else said, but also replace those wheels. They have A LOT of gunk of them not making things any better.

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Another potential source of excess friction is that power from motors to wheels is transferred from the larger 36T gears to the smallest 12T gears sitting on the final axles.

It seems to me that with extra friction there is simply not enough torque from a single motor powering each side, which leads them to quickly overheat.

For the drivetrain, I would use direct gear ratio, but if you must gear it up, I would try to pick the next larger gear sizes like 60T to 36T.


Nah, 3:1 gear ratio op

Ur robot must be insanely fast

Looks like 2:1 to me…

Yep, 24T and 12T.

I always found using gears in vex IQ to not be the best idea for a drivetrain, especially not that many. It creates unnecessary friction for the not so powerful motors, and since there isn’t much stress being put on the gears, chain isn’t likely to snap. I maybe had one or two chain snaps in 6 seasons of IQ using chain every year.

Of course it’s a little late to switch now. Just follow the advice of the rest of the folks here and make sure nothing is rubbing and find the source of the white dust in the pictures you sent.

Maybe a good tip for next season however.

Chain can take up a lot of valuable width in the robot. Everything has a tradeoff. Using washers properly to minimize friction does not cause discernable velocity difference for drivetrains.