Victors verses Jaguars?

[Chris is me]

Originally Posted by RyanN

[*]Over-current protection

I'd argue this is a huge con. You already have circuit breakers for over-current protection, so they're redundant. But to make things worse, tripping overcurrent means you lose control of your drive for three seconds. You can only change this time delay if you use CAN, which is itself unreliable.

[*]Tried and trusted for many years (884 since I believe 2004, correct me if needed, and 883 before)

This is a con?

I'm not using a Jaguar on a robot as long as possible. I'm just not willing to compromise reliability. Victors do exactly what they're told.

[Cory]

To be accurate, Victors only cost $5 more than Jaguars and undiscounted Jaguars cost $20 more than Victors.

[PayneTrain]

Thank you for posting this. Our team had a not-so-minor issue in 2008 (feel free to look at TBA. There you will find plenty of not-so minor issues like opponents ripping out our electronics board and other general design failure) which involved an inoperable fan on a Victor to result in our own mini-Chernobyl. However, we go through problems every year during testing Jaguars, and they magically work during competition. Malfunctions this year rendered our drive train inoperable for stretches of time.

I want to go back to Victors because of this.

[Kusha]

Originally Posted by PayneTrain

Thank you for posting this. Our team had a not-so-minor issue in 2008 (feel free to look at TBA. There you will find plenty of not-so minor issues like opponents ripping out our electronics board and other general design failure) which involved an inoperable fan on a Victor to result in our own mini-Chernobyl. However, we go through problems every year during testing Jaguars, and they magically work during competition. Malfunctions this year rendered our drive train inoperable for stretches of time.

I want to go back to Victors because of this.

We had the same problem. I'd say go with victors, you don't have to deal with can-bus. We had so many problems with jags that we had basically skipped 8 matches during regionals.

[RyanN]

Originally Posted by Chris is me

I'd argue this is a huge con. You already have circuit breakers for over-current protection, so they're redundant. But to make things worse, tripping overcurrent means you lose control of your drive for three seconds. You can only change this time delay if you use CAN, which is itself unreliable.


This is a con?

I'm not using a Jaguar on a robot as long as possible. I'm just not willing to compromise reliability. Victors do exactly what they're told.

Yep, that was supposed to be a Pro for the victors. My bad.

Also, I did put the over-current in the Cons as well... It caught us too much, plus by my understanding, the shunt resistors starts to wear out pretty quickly too, so the Over-current starts to kick in earlier and earlier.

Also, to be fair, I believe the Jaguars were design to be used with CAN, and the PWM control was a second-thought. Not a good excuse, but you gain so much functionality with the CAN network.

[pfreivald]

Originally Posted by RyanN

but you gain so much functionality with the CAN network.

In my very limited industry experience, I've seen too much vapor-ware to trust 'functionality' that hasn't been proven...

You can substitute "very limited industry" with "decade-long FIRST" and make the same statement. Unfortunately, FIRST tries to vet too much unproven product. For a $6K price tag (at a very bare minimum), I expect products to work out of the box.

[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.