Robot doesn't drive properly

So after changing our battery on Friday, we went to turn the robot back on, and it was immediately having problems. When I would go to push on the joystick, the robot would not move, but I would see the voltage drop significantly via the driver station (it was getting down to 7 something) and then the robot would just suddenly jump and start driving. And then if I used that same side again, it would be just fine, however if I tried to use the joystick for the other side it would do the same thing. As long as i use the same side repeatedly, it didnt have a problem, but as soon as I would switch sides, it kept doing the same thing again. I looked over all the wires, and nothing that I could see would be shorting out. I should also mention that the Talons would flash slowly and then get faster until the lights were solid before it jumped.

Do you only have one battery? And what was it doing, before you charged it Friday? Had it been sitting for a long time, discharged? Sounds like maybe it’s damaged beyond repair, although you might try charging it and using it again several times, to see if it regains some capacity.

You said you looked for shorts…but did you look for loose connections? It’s not the same thing as a short, but causes most electrical problems on robots.


It sounds like your Robot battery is not able to supply enough current to meet the demands of the drivetrain! You mentioned that you had just switched your battery. I would check to make sure the nuts that connect the battery wires to the PDP are all VERY tight. For more info see:

Edit: @MrForbes beat me by one second haha


We tried with a few different batteries, and it was working perfectly fine before we changed the battery

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Tell us about how you checked for loose connections in the wiring from the battery to the PDP

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I went through and both visually inspected connectors to make sure everything was tight and gave everything the wiggle and tug test and nothing was loose.

A video of this might help. Also, your battery was not stored on the robot right?

Do you have lock washes under the bolt head?
We had a BAD experience with forgetting to install lock washers. It cost us going to World’s.

Did you test ALL bolted AND crimped connections from the battery to the breaker to the PDP and back? Did you do a pull test on all the connections in the wiring from the PDP to each motor controller to the motor and back?

It may also be useful to use a bright flashlight to look at all connections for anything shiny, especially the ones where there is a 12V wire next to a 0V wire. I have found quite a few stray strands (visible as something shiny) causing intermittent short circuits on the 12 V supply on the PDP, VRM and PCM that lead to the sort of problem you are describing. The wires going into the Weidmuller connectors on the PDP, VRM and PCM should have the insulation extending into the holes for the wires so there is no exposed conductor visible (as something shiny).

Ill try to get a video later, and no, both of the batteries that we tried came fresh off the charger.

We used a brand new breaker with all of its lock washers, and the lock washers went back on to the pdp when it was installed


So now after sitting over the weekend, the robot is working just fine, so im not sure if there was a software bug or what exactly was happening.

If the code didn’t change, it’s probably not software.

If the one thing that changed was the battery, you probably want to examine the battery and its leads. Anything out of the ordinary is suspect. And I do mean anything.

You don’t happen to pick up batteries by the cables, do you (as a team)?

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I would strongly suggest doing the checks I suggested. At one event I was volunteering at, I was asked to help 3 teams that had the same issues your team is having. All three of them had stray strands intermittently shorting out the 12 V supply, causing their radio or Roborio to reset randomly.


It was the exact same battery we ended with on Thursday, so there was absolutely nothing that changed over the weekend. And my team always holds it by the battery, I haven’t noticed anyone holding it by the cables.

Any chance you had a voltage ramp going in your code? It sounds like the Talons were getting low throttle signals at first.

I had the joysticks all the way forward so it should have been moving full throttle right away

That does not follow immediately. There are lots of ways to program the robot which will ramp the drive voltage. It could be in your code, or in various settings in the motor controllers. Many teams put in a ramp by default, for example, to not jerk the robot (maybe tip it over) and reduce brownouts.

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I figured out what the problem was. After we changed the battery, I forgot to re-deploy code, and the code that was on the robot already had some of the drive motors turning in the wrong direction, so that’s why it wouldn’t move, and then something must have given up and that’s why it suddenly jumped.

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