Jittering Motors Problem

Yes its another questing involving jittering motors. I have a 6 motor drive with some high speed gearing. (1:1.5 with high speed motors, so essentially turbo gearing) It had been working quite well until yesterday when I finished the final wiring on my robot.
When I drive it, after about 15-20 seconds the motors start jittering as though they had stalled or had conflicting commands, the motors aren’t even slightly over-worked, as this robot can drive for 10 minutes without stalling (actually I haven’t stalled it yet) and it can push cubes under the fence. I have double checked the code - although I haven’t changed that since it was working - and some of the wiring, but I haven’t come up with anything yet.
Two drive motors on each side are wired together with Y cables, the other two are single wires. They are then wired to the power-expander and from there to the cortex. Prior to these problems they were wired directly to the cortex along with everything else. They are also on separate internal fuses, Ports 2 and 3 than 8 and 9.
Does anyone have any suggestions?
Here’s a picture, although I’m not sure why a picture would be usefull, but have a picture anyway.

(Please ignore the broken line tracking sensors)

Do both left and right sides jitter?
Do they jitter if you lift the robot off the ground so the wheels can move freely?
So all six motors on one power expander? That places them all on one 4A circuit, the fact they are split on the cortex now doesn’t matter. What does the led on the power expander do? Does it go yellow or red at all?

Things to try/check:

  • Read @jpearman’s post (that showed up literally as I was typing mine)
  • I would go even a step farther than lifting the robot off the ground: run 6 motors free-spinning (detached from your robot) with the same wiring
  • Try creating a super-basic program that does nothing other than allow you to drive the robot (control the drive motors). That will determine if the issue is in the code or wiring/hardware

Both sides jitter simultaneously, and they continue to jitter when the robot is lifted off the ground.
I didn’t think about the single circuit in the power-expander, I expect that’s the problem. I will try moving half of the wires so that they plug directly into the cortex.
The colour of the LED doesn’t change.
The recovery only takes about 5 seconds, then I can drive for another 30, depending on the aggressiveness of my driving of course.

The code I’m running is a very basic testing code, thus I can narrow the problem down to a wiring/hardware issue.

Thanks for the responses.

try checking if it is a broken motor or a motor in the wrong direction, that can cause jittering sometimes.

to me it looks like there is quite a bit of friction in the drive, try adding in 1 more chain link for each chain and take some spacers out to make it so it is very easy for the motors to move when the robot is lifted up.
another thing you can do is make sure everything is lined up and make sure there is a bearing block on every moving shaft.

Thanks everyone, with your help I got the problem sorted out. It appears I was overloading the power-expander. My solution was to simply move two of the drive wires to the cortex, replacing one of them with the claw motor. It now works just as well as it did before, so well in fact that I thought I could try and make it a bit faster, just for fun. Here’s the result:


Obviously that wasn’t sustainable so I changed it back to turbo.

I would suggest to mark this as the answer to your problem

Yeah, rather good idea.

I managed to recreate the issue again, but this time its just because I was unknowingly applying full power to the claw when holding objects, a programming issue, but it made it definitive that the power expander fuse was the problem.

@Alex Baggins My problem was my new HS lift was overdrawing power from the cortex causing it to Jitter so we moved the drive motors to the main cortex and moved the 2 splitters to the power expander.

P.S. I am soon including a 4 turbo drive into my robot. My robot is Ultra Light and weighs 8Lbs, also the Drive has extremely little friction. Would you give me any suggestions for when I go turbo? I am using no chains nor gearing that can cause friction. My robot is currently 4 motor HS set up and even with 30 min of driving it won’t burn out.

My main suggestion for going turbo would be to make sure that you have all the weight evenly divided on the robot. Even though your robot is so light, having a lot of weight on one specific wheel will cause it to stall and eventually cause the whole robot to stall.

@The Electrobotz @Alex Baggins
My robot had a tendency to flip so I added pop-out anti-tip which works but when the robot dumps the front 2 wheels come off the ground causing stress on the back motors, should I go with this and tell my driver no not abuse the drive when dumping. What do you think?

P.S. Thank you for the quick reply

What part of the dump do the anti-tip bars touch the ground?

@mwang17 Capture2.PNGCapture4.PNG

You should be OK to run this. Test it to make sure though.

Thank you I sure will