Brownout with NEW batteries?

We are having a strange issue… We are browning out with brand new, fully charged batteries. This only happens when we turn in any direction. We also hit 10 volts when we drive forward. We have double and triple checked our connections and no loose ends. We are using a 2016 AM14U3 drive train (no, we have not used it before). We also checked our motor controllers and they seem to be working correctly.
Any Ideas,

Put it up on blocks, and see that all the wheels are turning in the correct direction.

make sure the center wheels are a bit lower than the end wheels. you might be able have assembled it upside down.

They are moving in the correct direction. We were trying to drive it and this issue came up. I will check the wheel position.

You would notice straight away if a U3 were upside down. The wheels (assuming 6") would stick out only 1" at the bottom and 2" at the top.

What are the wheelbase and track width of the robot? If you assembled a long chassis with short front/rear caps, you could easily create a lot of scrub force. Also, how heavy is the robot?

With the robot disabled and placed on carpet, how much force pushing on the corner of the robot is needed to turn? If it’s more than one finger of force, there’s too much friction to turn.

Have you tested the motors individually through code? One motor may be trying the run backwards.


Put it on blocks first and verify everything works without browning out.

Then, if it’s on the ground and it browns out then you need to figure what the geometry problems might be.

One of those things is making sure you have the drop center.

Yeah, we tried that and it didn’t change anything. The dimensions are 28 by 27. The weight is 85.6 lbs.

You are able to use the driver station to see how much amperage your drive train is drawing . Have you checked?

How do you check that???

Which “that”?

That shouldn’t be the problem.

Are you sure your connections are all actually tight? If you try to use your fingers to rotate each and every one of the lugs screwed to your batteries, main breaker and PDP, do any rotate even slightly? If they do, the connection is not tight enough. Have you done a pull test on each and every crimp and spring connector (Wago and Weidmuller)?

Check to see the gearboxes are assembled correctly, it is possible to flip gears inside the toughbox and end up with a lower then intended reduction, this will cause the motors to have to provide more toque to get the drive train rolling and up to speed, this increased power usage on 4 Cim motors could be enough to cause it to brown out

What I’ve said above would also explain the voltage drop when driving forward, then with scrub in play as the robot turns, it is just enough to push it over the edge to a brown out.

Have you checked the connections on the heavy duty battery feed cable? They connections at the PDP should be very solid and tight, and make sure the battery terminals are super tight. (Bad battery connections will also be read by the Battery Beak as internal resistance, and the Beak will tell you its a bad battery). Our team checks the motor direction on the gearboxes by pulling the PWM cable to each motor controller, and thus run one motor at a time to verify proper direction. You can also tell if you have a damaged motor or a motor where the power cable is open, making the motor just go along for the ride and not pull help power the trans. If your turn is still pulling down the voltage, it may be a weight balance on your bot. The lower center wheel is to allow the robot to ride on the back wheels, and minimize the front wheel scrub (side force friction). Another way to reduce scrub is to use Omni wheels, but that will make your robot easy to push around. However, if that is necessary, it may need to be done. You don’t want to be browning out on the field as the field inspector will come over and require you solve the electrical problem in your robot. (They will get you help, too, but its better to solve the problem before you go to competition.).

I’ve found that 9/10 times this is the cause of high voltage drop issues. Really double check every connection on the battery lugs, Anderson connector, main breaker, and PDP. Check for loose lugs, poor crimps, failing wires, etc.

If you can’t find the problem, Minnesota seems to be pretty full of experienced teams. Maybe you can get someone from one of them to drop by and help diagnose your issue. Ryan Hedlund and Laurie Shimizu are the senior mentors for MN. Maybe you can reach out to them to put you in contact with someone.

If you feel up to a bit of a drive Friday evening, 4607 is holding their annual Spec Check in Becker. I’ll be there (starting around 6, unless I get out of work early), as will several of our CSA’s. Between us, I’m confident we could find the problem and help you fix it!

Have you tried turning the drive train by hand? That’s always one of the first things I do - you can usually tell if there is an unusual amount of friction. If there is, then it’s a mechanical problem. If not…

Check all connections, starting at the battery. If you can move them by hand, they’re too loose.

Remove the electrical tape/heat shrink around the lugs on the batteries, main breaker, and PDP to visually inspect the crimps - I’ve seen a lot of bad crimps over the years cause power problems.

Do you have a battery beak? Use it on your batteries to see what condition they really are. Just because they are brand new doesn’t mean they can’t be bad - manufacturing defects can cause them to be dead immediately. It’s rare, but can happen.

Posting the DS logs showing total current draw and the individual channels would be helpful!