Victors verses Jaguars?

[Vermeulen]

Also, IIRC you can't run the window motors with jags.

[Grim Tuesday]

We did, and had no problems.

[slijin]

Originally Posted by Vermeulen

Also, IIRC you can't run the window motors with jags.

This is false. Although you -can- run window motors with jaguars, most teams experience serious problems doing so. The reason is that the linear output current of jaguars in conjunction with the torque necessary to turn a window motor engages their locking pins, in turn locking the entire physical system. For more details of just why exactly this happens, I suggest turning to Ether or a mentor who's much better acquainted with this situation than me.

That being said, there are numerous threads regarding the pros and cons of victors and jaguars. It ultimately boils down to reliability v features, respectively. In my two years I've witnessed the death of nary a Victor, and stared in disbelief at a Jaguar shipment with a 60%+ out-of-box failure rate, not to mention a Jaguar going up in magical blue sparks for no good reason (no shorts, no scrap metal debris, no physical damage unless it was from the factory).

[Ether]

Originally Posted by slijin

For more details of just why exactly this happens, I suggest turning to Ether or a mentor who's much better acquainted with this situation than me.

I'm not sure anyone knows for certain why this happens, but one prevailing hypothesis is that the PWM frequency of the Vic is low enough to create torque ripple near enough to the resonant frequency of the pins to knock them loose and keep them from jamming.

[Al Skierkiewicz]

Originally Posted by Ether

I'm not sure anyone knows for certain why this happens, but one prevailing hypothesis is that the PWM frequency of the Vic is low enough to create torque ripple near enough to the resonant frequency of the pins to knock them loose and keep them from jamming.

I believe that the low mass of the locking pins cause them to oscillate into a lock mode when the motor is powered through the 15kHz switching of the Jag. Removing the locks fixes this problem in many applications. While locking is still an issue with Vic, the problem seems to occur far less frequently.
While the newer Jags have gone to lower "ON" resistance FETs, the manufacturer has lowered the number to two in each leg while the Vic remains at three. I think this gives a slight edge to the Vic in terms of dissipation at sustained high currents. No one has mentioned that the Vics are conformal coated. This coating prevents a lot of the contamination that is prevalent with the Jags.
Heating of the CIMs over a two hour practice/demo is not unusual. The CIM motors are sealed and intended for intermittent duty. Internal heat has very small paths to dissipate to the outside air.

[Hawiian Cadder]

personally, i would say avoid jags for any of the high current motors. the cims and rs-775's generate a lot of electrical noise, and this is what we believe to be the culprit behind our CAN problems. the Current control is very nice for some things. i think that a mix of jags and victors would probably be ideal. jags on the smaller motors where more finesse is necessary (550's, 395's) and victors or spikes everywhere else.


another reason to use victors on the high current motors is that they are typicaly in the drive-train, which means that they should have encoders on them already, and if that is the case then the sensing capability of the jag is unneeded. with voltage and speed, current and anything else you want can be calculated.

[Ether]

Originally Posted by Hawiian Cadder

the cims and rs-775's generate a lot of electrical noise, and this is what we believe to be the culprit behind our CAN problems.

Is this just speculation, or has your team run designed tests to verify this?

[Hawiian Cadder]

at CMP another team appeared to be having the same problem ( motor pulsing ) we had already solved the problem with the timeout, and that had helped tremendously, however we were still getting intermittent dropouts in the Can buss. when we talked to the other team (i dont remember name or number, maybe 399?) they said that they had been having the same problem and that attaching a filter capacitor on the leads of their motors had helped tremendously. another thing that lead me to this conclusion, is that we never had any problems with the can while we were testing our lift or manipulator, which were all rs550s or fisher prices. when we tested the drive however, the can network continued to drop out intermittently. the FP on the lift was drawing at least as much current (approx 30 amps continuous) so i was left to think that electrical noise was the culprit. we have not done any tests, but before next season we might try the filter capacitor trick and see if it solves the problem.

[AustinSchuh]

Originally Posted by Ether

Is this just speculation, or has your team run designed tests to verify this?

While it may be speculation, I've noticed what I believe to be a similar thing. I'd love to get a scope in the same spot as the robot though and see what's really happening though...

971 was testing our elevator, and when we would tell the control loop to move the elevator down a foot, (with a FP, and also with a FP and 775 both running off Black Jaguars), we could reliably get the robot to reset the Jaguars and loose communications. This happened more often when we had lots of D in the control loop. I haven't seen anything like that in the drivetrain with CIMS and Jaguars when doing control loops.

[Jon Stratis]

Originally Posted by Hawiian Cadder

personally, i would say avoid jags for any of the high current motors. the cims and rs-775's generate a lot of electrical noise, and this is what we believe to be the culprit behind our CAN problems. the Current control is very nice for some things. i think that a mix of jags and victors would probably be ideal. jags on the smaller motors where more finesse is necessary (550's, 395's) and victors or spikes everywhere else.


another reason to use victors on the high current motors is that they are typicaly in the drive-train, which means that they should have encoders on them already, and if that is the case then the sensing capability of the jag is unneeded. with voltage and speed, current and anything else you want can be calculated.

FWIW, we've used CAN now 2 years running (for drive train and some manipulators), and haven't had any real issues with it at competition. Sure, it can be a little finicky when getting it all set up during the build season, but once it's working, it just keeps on working. further, we've only lost 2 Jags so far... one was bricked by a bad firmware update, and the other due (we think) to metal shavings. At least, its replacement worked just fine over 2 competitions afterwards! We've seen 0 problems using jags with CIM's.

[Kevin Sevcik]

57 has used CAN for 2 years and we're heading into our 3rd this year. We've had occasional problems with the CAN network dropping out, but I'm pretty certain they were all self-inflicted. Things like the CAN-Serial adapter coming loose from the cRIO, or a finicky terminator that would occasionally short if you looked at it funny. I think CAN is plenty reliable if you're careful about your wiring. The major drawback is that a bad connection will take your whole network down, instead of a single motor.

As for reliability, we've had a handful of the Gray Jags go bad on us, but we haven't lost a black one yet. Again, I think being careful around your electronics is the main thing. The Jags are more susceptible to metal shavings than the Vics, so you need to cover up your electronics if you're producing shavings. Which you should be doing in any case, even if your Vics are less likely to fail because of it. There's plenty of other stuff in the control system that's vulnerable to metal shavings nowadays.

[dellagd]

Originally Posted by Kevin Sevcik

57 has used CAN for 2 years and we're heading into our 3rd this year. We've had occasional problems with the CAN network dropping out, but I'm pretty certain they were all self-inflicted. Things like the CAN-Serial adapter coming loose from the cRIO, or a finicky terminator that would occasionally short if you looked at it funny. I think CAN is plenty reliable if you're careful about your wiring. The major drawback is that a bad connection will take your whole network down, instead of a single motor.

As for reliability, we've had a handful of the Gray Jags go bad on us, but we haven't lost a black one yet. Again, I think being careful around your electronics is the main thing. The Jags are more susceptible to metal shavings than the Vics, so you need to cover up your electronics if you're producing shavings. Which you should be doing in any case, even if your Vics are less likely to fail because of it. There's plenty of other stuff in the control system that's vulnerable to metal shavings nowadays.

Lucky!

Ours went bad before the final match of eliminations. That was a pain...