Yesterday I had the basic driving robot with two large motors, but I could not get both motors running at the same time. I had the tank control programming block, with both motors set to 50% and when running the program both motors would start and one would continue spinning, but the other would stop after only 1 or 2 degrees of rotation.

First I thought it was a problem with the motor, so I replaced it with another motor from another set, but the problem remained. When I switched the ports it was the other motor that would not keep running. I tried different ports, changing the cables and restarting the brick but nothing helped. Checked the rechargeable battery to see if it was a power issue, but that was full. I did this in a class with several other EV3 sets using both large motors and none of the others had this problem.

I then used the programming block for a single large motor and tried both separately and that worked fine. But when I put two of those blocks after each other to start the motors sequentially again the second would not run after an initial click.

When I wanted to troubleshoot it further after I got home everything worked fine, which makes it even stranger. That also suggests it was not the battery box as mentioned in this post.

So I hope maybe someone has seen this before and can tell me why this happened and what to do should it happen again.


EDIT: I found the faulty EV3 (it was number 9, not number 6....). So I was able to do more troubleshooting. Attached a screenshot of the various programs I tried with comments.

It looks like port C is consuming more power than the other ports (motor runs at a significantly higher rpm). And this shuts down any motor running at the same time through one of the other ports. combining two of the other ports (e.g. A and D) works fine.

Any thoughts on how this can happen?

enter image description here


  • Hi jboss and welcome to Bricks.SE! Can you post a screenshot of your program, so that we can see what exactly is happening? – zovits Dec 19 '19 at 9:10
  • I'm not 100% sure it was like this (it was yesterday and everything is removed and taken apart again) but it was the basic driving robot. – jboss Dec 19 '19 at 11:34
  • Maybe try another battery pack? – Alexander O'Mara Dec 19 '19 at 18:42
  • I tried another battery pack, no effect. I also tried resetting the brick, no effect. But when I used motor control from the menu on the brick itself I could run both B and C simultaneously. – jboss Dec 20 '19 at 8:35
  • And another possible cause, I updated the firmware of the brick, but that also made no difference. – jboss Dec 20 '19 at 8:46

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