Voltage issues

Our robot has had constant issues with voltage. Earlier we had 2 motor controllers controlling 4 motors (1 motor controller per motor) and have since changed that because of voltage problems, or so we thought. We now have 4 motor controllers controlling 4 motors and we are still having voltage issues. We have experimented, rewired, and looked everywhere trying to figure out why our voltage drops so much. Do you guys have any ideas why this is happening?

It could be you have a bad battery. Use a battery beak to check. Could also be because something is adding unintentional resistance to the system. Could also be because you have bad electrical connections. It helps to post a picture of your driver station logs

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Have you run through the other troubleshooting procedures from your other thread? What were the results?


We had fixed the issue and then it happened again. We tried the same procedures and dont have a clue what is wrong.

I think it’s time for you guys to do a deep dive into your wiring.

Without the battery in: Start at the Anderson connector for it. Work to the main breaker, to the PDP, and through every branch circuit.

You’re looking for, in no particular order:

  • LOOSE connections
  • Bad crimps (pull, and if they come out, they’re bad)
  • Excess insulation in the PDP/other crimps and connections
  • Wire whiskers, particularly ones that bridge between two wires
  • Worn wire insulation, particularly if you can see copper
  • Excessively long wire runs
  • Undersized wire–remember that a larger gauge number means a smaller wire–and smaller wires mean it’s harder to push the current through them easily.
  • Properly-seated PDP breakers

Also, disconnect non-drive circuits for now.

Clarifying question: What voltage does the robot drop to, from what? It’s not all THAT uncommon to drop to, say, 10V during operation–8V on the other hand could point to something more serious. 6V would be exceptionally bad.

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The voltage is dropping below 7 volts and it’s making our motors run in a choppy manner. To put it into perspective, it’s like lag on a video game. Also the right side of our robot does not move…we have checked the code, the can ports, and the crimps multiple times. We have had professionals solder our wires (electrician mentors) and still nothing. I’m starting to think that our PDP is busted but we didnt want to draw any unreasonable conclusions to what might be causing the issue.

I would open up the PDP using the screws.

Look for oddness in the traces.

Before you do that… try moving the wires to another port on the PDP. Could just be a dead port; that can happen on occasion.

This also happened to us cause our battery was bad. Check ur battery too

Can you upload your driver station logs? That might help us track down the problem.

I would strongly suggest that you and your team print out the list of tests that @EricH has posted and work through it again, thoroughly, and check off each test as it is completed.

Verify that all bolted connections (battery to cables, cables to PDP, wires to motor controllers such as SPARK) are tight. If the lug can be rotated with finger pressure, it is not tight enough.

Lastly, you may want to find another more established team near you to look over your robot. You are asking about issue you know about. You cannot ask here about issues you do not recognize. Some issue are most easily found by someone looking at your robot in person.

I would add the following:
How old is the battery?
What wire gauge you use between the battery… Breaker… Pdp?
Are the battery connectors clean? (sometimes some rust forms there…)

The materials the battery connectors are made from typical don’t rust. I have seen many where the silver coloured plating has worn off the contact points. That will increase the contact resistance.

It may also be possible your right gearbox could be seizing up, causing its motors to draw excess current. A clamp DC ammeter could reveal a motor that may be drawing excess current and loading down your battery.

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A lot of thoughts have been posted on this. However, there are a some unknowns that need to be
clarified before too much more is offered.

1: What are the four motors in use?

2: What motor controllers are driving the motors?

2: What is the gear reduction and wheel size on the drive train?

3: If you have a CTR Battery Beak: Can you use it and post the internal resistance of the battery?

4: Can you post the collective current draw of the four motors when Vbatt drops to 7V from the drive station log? The Rio operates down to 4.3V, so that log is telling a story. The 7V issue is likely causing the WiFi to power cycle (this is a total guess on my part, but that is the specific voltage level where this symptom will present)

The power is being consumed somewhere in the electrical plant. Once we have answers to the above questions you can narrow the focus on connection points and offer helpful suggestions.

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