Battery drains to quickly

While making our competition robot we’ve ecountered a problem with the batteries(I think). When we run our robot longer than two or three minutes it slows down incredibly. After a five minute break the robot will run at normal speeds until it slows down again. We started using a vex power spliter, but are still having the problems.

Any help would be appreciated,
Thanks in advance

You may be overheating the motors. If it were battery drain, it wouldn’t really recover after a 5 min break, but that is enough time for the motors to cool down. You might try changing your gearing to reduce the load on the motors, or you could put more motors in parallel so they share the load.


  • Dean

Dean is most likely right.

Another thing to check is friction in your drive train. A little extra friction can cause a lot of extra work for your motors. Make sure your axle holes are perfectly aligned, that the bearing blocks (“delrin flats”) are not squished and binding on the axles, and that the lock collars are not squeezing against a bearing block or frame. You *are *using bearing blocks, right?

Ok, so my problem is with the motors not the battery. Let me explain how our motors are set up;

  1. We have one motor for each rear wheel, both wired together with a Y-cable

  2. The motors are both mounted on the inner frame facing out, we knew that this would cause the wheels to spin in opposite directions so we compensated with three gears on one side and two on the other.(no noticeable speed difference)

  3. Our gears in order from the motor to the wheel are: Large-medium and for the odd side: Large-medium-medium

  4. As stated previously these motors are powered with two 7.2v batteries via splitter

Thanks Dean your deduction seams reasonable. Can you explain what you mean by running the motors in parallel, also do you have any recommendations on optimizing our gear ratios?

Thanks for your response,
We are just using the basic pieces that came in our vex kit(sorry i’m not sure of the actual names, apart from washers and spacers)
I’ll post pictures later of our set up, if it will help.
Can you explain what the bearing blocks and lock collars are, thanks.

Picture of “shaft collars” (our team calls them lock collars):

Picture of “delrin flats” (our team calls them bearing blocks):

Both are on this Web page:

Oh ok, i understand what you mean now.
I never thought about that problem before, but now that you mention it we do have our locks tightly pressing against the bearing blocks. As a matter of fact in some areas we didn’t even use washers between the locks and the bearing blocks.
I’ll definitly fix that tommorow and see if that will resolve my issue.

Thanks for your input