Victors not synchronized - dual motor train

[roknjohn]

Our bot uses the dual motor kit tranmissions (2 CIMs left, 2 CIMs right, and 4 884s). We noticed some rather loud motor noise (over and above the loud tranny noises) occasionally when accelerating. The sound is best described as a stalled CIM. We tried using Y-cables for the PWM signal to the two victors on each side. The noise still persists, though, like I said, is intermittent.

Funny thing though, if we wire both CIMs to one victor (yeah, I know its not legal) the problem is solved!

So, if the input signal in the same to each victor (via the Y-cable), how are we sure that the output is the same? Is there a way to calibrate two victors so that they behave the same with identical input signals?

John

[Matt Krass]

My team had a similar problem, we solved it by recalibrating both Victors simultaneously. Just use the guide on ifirobotics.com to calibrate, and do both at once.

Go to to the homepage, click Victor 884 on the left side and then get the User Guide PDF, it's in there.

[sanddrag]

Matt,
Did you try doing them separately and it didn't solve it? I'm asking this because that would mean we have three of them to do at once.

[Matt Krass]

We didn't try them separately no, it didn't seem logical, we want them to be in perfect synchronicity and our joysticks aren't that good with that, so for us the logical solution is simultaneously calibrating them, I've found its very easy to do with multimeter probes in the calibration pinholes. But we only had two, but two people, three probes, not so hard, then just move one joystick forward/backward/etc repeat with the other side. It's not very difficult.

[jimfortytwo]

It seems incredibly unlikely to me that slightly mismatched voltages would make any noise whatsoever. I'm inclined to say you've misdiagnosed your problem, unless you're calibration is ridiculously off. We're on our second year of quad motor drives, and have never experienced such a problem as the result of mismatched voltages. If the voltages are slightly different, all that should happen is perhaps a slightly uneven load sharing-- but that ought to be a silent affair.

[Shu Song]

That noise might just be due to very unlubricated gears and causing a lot of friction and thus causing the motor to stall. Trying lubricating the gears with something and it should lessen the stalling of the motors. I seems very unlikely that the victors are reacting differently to the same data sent to them, at least in my 2 years of electronic experience.

[sanddrag]

We were getting really bad buzzing. Part of this is due to the Fisher Price being combined with the two Chias. At startup, I assume they are "fighting" (not spinning opposite directions, but not spining at the same speed) a little bit. Anyhow, I'm not exactly sure what we did, but we either calibrated the Victors or switched the motor polarity (and pwm values) or both. Anyhow, the buzzing is almost completely gone, only very minimal (due to drag and the FP). It was an electrical, not mechanical induced sound.

[Al Skierkiewicz]

A simple way to get everything calibrated is to remove all the breakers but the one you want to calibrate. Go through the calibration procedure. (remember the values are not stored until you release the button.) Then swap breakers and repeat until all the controllers are calibrated. It is not unusual to have a little "chatter" at dead stick but if you think it is a problem, increase the deadband and see if that fixes it. When you have two different motor types running in the same transmission, you are likely to get noises that are combinations of the two that you never heard before. Just be sure that each motor is adding to the overall output, that no motor is drawing more than expected currents and that all motors are running in the same direction for the same input. (removing breakers helps on this test as well.)

[Mr. Lim]

Adding to Al's suggestion:

When first energizing everything, program, test and check one motor at a time. Even if it is a dirt simple arrangement.

Pull all the breakers. P

Put in a breaker for only one motor.

Program it, test, and note the direction it spins in vs joystick motion.

Pull the breaker out.

Put one in for the next motor.

Program it, test, and note the direction it spins in vs joystick motion.

etc.

From a team who has built quite a few 6-motor drivetrains, we can safely say that motors running in opposing directions is a VERY bad thing. Avoid it at all costs through just a little bit of patience and care.

-SlimBoJones...

[Rickertsen2]

Somwhere i read a claim that the speed controllers are perfectly calibrated to work with ifi controllers and that the calibration is only for using victors with rc systems that lack trim. I don't remember where i heard this, but it is very wrong. On one of our 4 motor drive prototypes, the speed controllers were soo off that it was impossible to trim the joystick such that at least one motor was not trying to move at all times. The problem was easily fixed by calibrating the speed controllers.