Do not use Jaguars with window motors

My team arm is lifted with two window motors on the same shaft. Because my team is new (2 years) we had only Jags , but the motors had a strange noise when they work together and couldn’t lift the arm often. To check the problem we tried the arm with just one window motor and it worked without problems but we wanted two motors because of the strenth, thank to our neighbours team 2630 we replaced the Jags with victors and it is now working.
Why it happend?
I think that the Jaguars are not giving a equal voltage or something so the motors are not in the same speed and opposing to each other.
Does someone have a clear explaination why it happened? because I heard on other teams that it happened to them.

You will probably find what your looking for here. It’s a 9 page thread on Window-Jag compatibility issues.

This is a known issue for Chief Delphi and FIRST. It is the reason for R47-C that allows you to remove the locking pins from the window motor (helps with Jags and Victors).
The best practice with window motors is:
-run them with Spike relays
-never stall them
-don’t connect 2 of them together
They are very particular motors designed solely for car windows, not robots.

Interesting. Our team has used jags with window motors with no problem. But never 2 connected. One problem i could think of, would be that they are spinning at slightly different speeds, from either the motors themselves or the jags.

Running two of them together creates problems due to worm gears. As they run, their speeds will vary slightly, no matter how careful you are. This causes the worm gears to crack the casing or teeth, as they are being forced to backdrive, which they cannot do.

Actually, these motors DO backdrive, that’s why the locking pins are in there.

The tendency to backdrive for a worm gear system depends on the angle of the worm gear threads.

We have run the same two motors on one shaft in our practice bot for many hours and on our competition bot through 15 matches this weekend and never had a single problem.

And yes they do backdrive a little.

My general rule on window motors: Don’t use them.

Please remember there are slight electrical differences in the left and right motors.

Is there a list of known issues somewhere?

That would be nice, they kind get lost in all the threads in the technical subforums (many of which could be avoided by using the search or ::rtm:: ) . Among all the threads asking the same question or “is this <insert obvioulsy illegal thing> legal?” are some threads where the considerable collective knowledge actually identifies the cause of a tough problem and sometimes a solution. Recent examples are:
Issues with window motors and speed controllers (this thread and others but mostly the one last year that I linked)
The problems with Encoder::GetRate() (only works for half of your encoders)
RS-775 case shorts
Minibot inductors burning out
CAN TImeouts with v28 image
Feel free to add more.
Perhaps mods should sticky more, but people tend to glance over stickies :rolleyes: I guess the only way is to to glance over what is being discussed on CD, and focus on the important ones.

Our arm operates on two window motors, which are controlled by jaguars if I remember correctly, and we have yet to have an issue…

1178 used a window motor controlled by a Victor for our main lift (continuous rigging). Aside from the speed, we never had an issue with the motor. (The belt slipping, waiting for our main drive train parts to come in, jaguars frying (replaced all the drive jaguars (4) with Victors within 1 hour of uncrating the robot at the St. Louis Regional were several of numerous problems but with the window motor controlled by the victor, we never had a direct motor problem.)

Just adding that Team Max (1071) ran an arm with two window motors on a single shaft with two jaguars this year, also without issue over many matches and numerous hours of pre shipping practice time.

We did, early on, encounter some issues with the locking pins on the window motors when our arm was at its point of maximum torque, however some unrelated issues that changed the weight distribution of our arm seemed to mostly resolve them.

WE had similar problems with ourarm but they only showed up during competition which was the first time we had run the arm a lot at one time.