Why is my robot's motor struggling?

When i drive my robot that is not even that heavy it drives very choppy and it goes fast for about 1 second then it goes to slow and then it goes to fast again. I know it is not anything to do with the code and i also changed out the motors. It it because of the chains, because this is also my first time using chains on a robot.

The chains might be coming undone, then fix themselves, causing the choppy movement.

Can you share a photo of video of the robot? That might help in case it’s another problem.

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Sounds like a mechanical bind to me. Make sure you don’t have anything that’s clipping or rubbing as the wheels rotate. Could be a gear rounding out its center square hole; could be an improperly assembled tire that is out of round, could be lots of things.
Spin each side of your drivetrain by hand, feeling and listening for any resistance or vibration. Pay special attention if one side feels different from the other. That might point you in the right direction.

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How fast is the drive ratio?

This has happened to me, this could be due to a large amount of friction in your drivetrain on your chain is too taught.

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Sure ill send a photo later today my robots at school right now.

So do i have to loosen the chain or tighten it?

You would want to loosen it if it is too taught

But wouldn’t this cause it to skip turns because it is to loose. I’ll send pictures after, and should i like change the gear ratio so its medium to small gear because the motors struggling to. After i change the gear ratio should i turn motor drive velocity to 100% so it goes normal speed?

I would almost always run your motors at 100% power. As for the chain, if you are unlucky enough to find that not-so-sweet spot where one link of chain is too much of a change, you can put a tensioner in in the form of a standoff or something like that.

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Ok here is the picture

Sorry that the picture is dark and not that clear i took it using a chromebook.

Yeah, I’d recommend adding a link to the chain on either side. You can tension it with standoffs if needed, too. The sprockets for the drive don’t look completely aligned either, which could definitely add some more friction. The drive motors also need to be supported closer to the shaft, supporting them from the back like that won’t be enough. They look like they are bending down right now, which would definitely add more friction to the shaft.

Other recommendation:
The motor on the top rubber band roller seems to be bending outwards, or the plate it’s on is bending under the stress. I’d recommend bracing it to the other side.

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Ok, so ill add 1 link to the chain and then i build bottom support kinda shaped like a U to hold the motor in place because the back support is not enough? You said something about moving the motor forward but i cant because the chain wouldn’t be straight. What should i do to move the motor closer while still having a straight chain? What do you mean by bracing it to the other side do i just connect them together or do i lower the with of the gear so it doesn’t bend the plastic?

You can use a beam and some standoffs/angle connectors to make a box to mount the motor on, like this:

Yup.

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Yeah. If the upper motors are turning… causing the plate distance to vary, that would affect friction in the bottom motor shafts.

I would check shafts… make sure they are all straight. Your problem sounds like friction.