[FTC]: Tetrix motor controller weirdness with 4 motors

[Andrew Rudolph]

I would pull the motors out of their mounts and make sure they are all spinning the correct way. As Al said, it sounds like an over current issue. I have seen it where one of the motors on a side is shorting, putting into a break mode, so it causes the other motors to work harder to overcome the motor that's not spinning.

Otherwise I would rewire everything and make sure there are no shorts.

I would advise not daisy chaining the electronics on the robot, I have all my teams use Anderson Power Poles or Wago Levernuts, so if there is a wiring issue, everything down line doesn't go down. Especially since the voltage sensitive Samantha module is always the end of the line in the daisy chain wiring scheme.

[Al Skierkiewicz]

ak,
I went back and read over your post again. Am I correct that you have one controller feeding all four motors? Is that one controller output or two motors on one output and two on the other output? The motor controller is intended to power only one Tetrix motor per output. The controller has over current sense and will shut down if the current is too high or the temperature climbs above a certain point. If the controller is shutting down for a fault, it may fail to pass I2C signals on to the following devices. The specification sheet lists the current output for each motor circuit at 4 amps which is below the stall current for the motors.

[orangemoore]

I do have a question,

What is the purpose of running four motors off one controller?
There is no limitations to how many DC motor controllers you may have, the limitation is being only allowed to have 8 motors.

[CougarRobot]

http://ftcforum.usfirst.org/showthre...ull=1#post7575

2 motors per port has always worked just fine and is allowed. However, we have not yet done it with the new motors.

Is anyone else using 2 motors per port with the new motors?

[Scott_4140]

4 motors on one controller worked fine for us with the new motors at our first Qualifier.

Don't confuse FRC and FTC. There is nothing in the FTC rules preventing 4 motors on one controller.

Also, from the LEGO Education site:

http://www.legoeducation.us/eng/prod...or_tetrix/1648

The HiTechnic DC Motor Controller for TETRIX® connects to an NXT Intelligent Brick sensor port and will enable you to control powerful DC gear motors for use with TETRIX robots. The controller has two H-bridge outputs to control the speed and direction of two DC gear motors and is designed to connect to the TETRIX hole pattern. A four-motor robot can also be built by paralleling two motors to one channel. A total of four DC Motor Controllers for TETRIX and/or Servo Controllers for TETRIX can be daisy-chained to provide additional motor and/or servo outputs on each port.

--Scott

[aklego]

Originally Posted by Scott_4140

4 motors on one controller worked fine for us with the new motors at our first Qualifier.

...

This is good to know although I'll admit that I was hoping other teams w/a similar setup could reproduce the problem.

We have our qualifier this weekend that we'll run with our current setup and then return to troubleshooting after the event.

Lots of suggestions of an over-current fault but that seems inconsistent with the applied load. When we return to troubleshooting I'll instrument the controller and see what our current actually is.

[Al Skierkiewicz]

ak,
I received some info that the I2C passes through the controller in the event of a fault. So if you are having issues down stream from a particular controller, that device could have an issue or you could have a defective cable. However, there is still the off chance that one of the drive motors has excessive friction causing some high motor currents. You need to isolate the motors and see if you can find that issue as well. You mentioned in your first post that the motors are mechanically coupled, so it is possible that one of the motor issues is being coupled into the other. If you remove one electrically the mechanical problem still exists. Good luck this weekend.