[DFTF] Jags v. Vics...

[Joe Johnson]

This is part of a series of posts called Drinking From The Firehose on getting Dr Joe back up to speed on All Things FIRST.

Today's topic:
Jags v. Vics

I know I risk of starting a flame war, but it has to be asked.

Victors or Jaguars?

I have asked a lot of folks and here is what I have been able to find so far:

• Size: Victors Win
• Cost: Victors Win ($89 vs. $119 -- though I think there is a discount for FIRST teams, even after the discount, I think Victor remains lower cost)
• Reliability: Victors seem to have the public on this one, but it is not clear if this data is tainted by "the early years" of the Jaguars
• Smarter: Jaguars have an enormous brain inside that larger package -- not sure what that buys you in FIRST circles because we are limited in what we can do with it but it is there. Also can be a negative because some say the controller resets in some cases and causes flaky behavior (forgetting PID controls and otherwise going insane)
• More Features: e.g. Sensor and Switch Input, PID control (without the main controller even in the loop), current readings baked in (if you use CAN)
• CAN interface: pro and con for Jaguar - CAN can be better but the implementation has caused some problems (blocking controller code from running in some cases)
• Over Current Protection: Jaguars have baked in self protection (60A for 2 sec, 100A for 0.2 sec). Blessing and a curse. We already have a circuit breaker so we are double fusing in a sense but at the same time, not letting the electronics fry seems like a good idea too.

Over all, I think I am in the Jaguar camp because I am excited to implement some of the features available via CAN but I want to hear other input.


Thanks all,
Joe J.

[Andrew Schreiber]

Linearity of Response: Jag - The Victors are incredibly nonlinear, see the discussion in the 254 code thread for some very pretty pictures on it.

Reliability Under Load: I can't speak for overall reliability (I've used Victors since 2004 and never had a problem with one, Jags have only been around since 2009 and isolating Jag problems from NI problems has proved to be difficult for me). I can, however, speak about issues that arise when going from full forward to full reverse. Jags have, in the past, tripped a breaker during this action whereas Victors will do this all day. There are tricks you can do to fix it but if you want immediate response (within 3/4 cycles) you want a Victor in your DT. For most other places the Jag is probably fine though.

My money has been on Jags since 2010 because of CAN. In those two years we have never gotten it working as reliably as I desire on an FRC robot. Early reports I've heard have not been too positive of the CAN stuff for this year either. (High CPU load, not sure what the cause is)

As a result, I would recommend 884's in the drive train (despite their nonlinearity) and Jags elsewhere. While this will mean whatever loops you use to control your DT will suffer (PID assumes linearity) but the rest of your loops (arms, shooters, elevators, whathaveyous) won't.

[JamesCH95]

IIRC Jags have much better low-speed control than Victors, which became very apparent to me with our latest robot. We got CAN running last year, it was 100% reliable until that obnoxious field firmware issue reared its ugly head. I hope that will be fixed this year.

On pricing, what I found last year was: Jags are $85 from DigiKey, and Vics are $90 from Vex. Not sure if this is out of date or not.

When we used the brown Jags in 2010 we blew a couple of them in competition, very disappointing. When we used black Jags in 2011 we never had a single issue.

[Dad1279]

Originally Posted by JamesCH95

IIRC Jags have much better low-speed control than Victors, which became very apparent to me with our latest robot. We got CAN running last year, it was 100% reliable until that obnoxious field firmware issue reared its ugly head......

Burned by that issue also. It will take alot of convincing (or a mandatory rule) to use CAN again. Issue disappeared with PWM. We have had good results with the newer Jags the last two years, and will likely continue to use them.

We blew up a few Jags during testing the first (Lunacy) year, and switched to vics before ship, but post season testing proved they were static-electricity issues. Slick wheels on Regolith built up a charge like a Van der graaf generator.

[slijin]

Originally Posted by JamesCH95

On pricing, what I found last year was: Jags are $85 from DigiKey, and Vics are $90 from Vex. Not sure if this is out of date or not.

This is only true during build season; the Jaguar discount is implemented, I believe, immediately following kick-off. To my knowledge, there has been no discount on Victors since 2010.

[Cecil]

We have used Jags for the past 3 years, and haven't had too many problems with it. Last year, we tried to implement CAN using the 2CAN system, but we couldn't work out the bugs with it. Something with a packet read error. Nobody could figure it out, and we even tested every cable with an electronic tester. The error would slow the code down to the point where there was a 2-3 second lag between moving the joystick and the robot moving. We switched back to PWM's, and everything worked fine. So far, I think we have only lost 1 Jag to actual failure (was a tan Jag someone pulled the screws out all the way on). We currently have 2 sitting in the closet that may be dead, but we aren't sure. Eventually, they will (hopefully) be re-flashed with firmware, and will (hopefully) work again.

As for Victors, yes, they are still smaller in design. The PWM connectors on them sometimes don't line up with the cable, and there is no way to keep them in once they are there other than gluing them in some way. The Jags have a nice clip to keep the wire in place. Also, I don't think I will ever miss reaching my hand into the robot somewhere and jumping when I hit the fans on the Victors… I know I'm not the only one who has done that...

[JamesCH95]

Originally Posted by slijin

This is only true during build season; the Jaguar discount is implemented, I believe, immediately following kick-off. To my knowledge, there has been no discount on Victors since 2010.

Ah, I see. I haven't purchased Victors since 2005...

That's a big price advantage to the Jags during build season then.

[AdamHeard]

We prefer the smaller weight and footprint of the Victors, although I understand that isn't a concern to many.

We've used Jags in various applications, but what always worries me is the 100-amp fault mode. We've triggered this when we drove defensive bots at home with jags in drive over and over.

Can the 100 Amp reset be removed if you use CAN?

I'll just never feel comfortable with them in drive powering a motor that will draw 133 Amps routinely.

[flameout]

Originally Posted by AdamHeard

Can the 100 Amp reset be removed if you use CAN?

Someone please correct me if I'm wrong, but I don't think so. However, you can reduce the time it shuts off after a fault is detected -- I think the minimum is half a second.

I'm not sure if this change is persistent -- maybe you don't need to use CAN on the robot, but rather connect as a one-off configuration step (then you can use PWM on the robot). Does anybody know if it's persistent?

[AdamHeard]

Originally Posted by flameout

Someone please correct me if I'm wrong, but I don't think so. However, you can reduce the time it shuts off after a fault is detected -- I think the minimum is half a second.

I'm not sure if this change is persistent -- maybe you don't need to use CAN on the robot, but rather connect as a one-off configuration step (then you can use PWM on the robot). Does anybody know if it's persistent?

That is an inadequate solution. I don't really understand the point of this feature, one would assume the designers of the Jaguar are aware of what motors we use?

[slijin]

Originally Posted by AdamHeard

That is an inadequate solution. I don't really understand the point of this feature, one would assume the designers of the Jaguar are aware of what motors we use?

To be fair, bringing the Jaguars to voltage fault, from personal experience, is very difficult. Last season, we did mecanum for the first time; believing that the potential for better control Jaguars offered was worth the departure from Victors, we set up a test drive base with Jaguars on a serial-to-CAN interface.

We ran into a number of issues with Jaguars; one in particular led us to do a number of stress tests to see how easily voltage faults were induced. Although the testing was relatively casual and we recorded no quantitative data, the only way we could ever induce voltage faults was by rapidly shifting from full forwards to full backwards multiple times within a few seconds.

To elaborate on other problems we had, I have to say that the issues began the moment we took them out of the box; I believe 3 out of an initial order of 9 were defects (configuration could not be accessed, did not respond to signal control, etc). More died after we put them onto an actual drive base; the most notable example was one that released magical blue flame in the middle of a driving tryout.

Other issues we ran into include CAN issues that could not be properly debugged because of issues possibly related to the proprietary code (as we could not effectively isolate said issues).

One point that I'd like to raise, non-performance related, is the encoder I/O interface on the Jaguars. One of their selling points is that they can be configured to run their own individual PID loops with encoder input, but that feature is somewhat tedious to utililze. The encoder input is a 5-pin PWM setup, whereas the USDigital optical encoders have a 4-pin output (Jaguars can take an index signal that these encoders don't). Most teams would have to cut up the KoP 3-pin and 2-pin PWMs and solder them to the encoder wires, which I personally find to be a tedious implementation. The alternative, however, requires teams to own the tools and materials necessary to produce their own 5-pin PWMs.

[Jared Russell]

Originally Posted by slijin

To be fair, bringing the Jaguars to voltage fault, from personal experience, is very difficult...the only way we could ever induce voltage faults was by rapidly shifting from full forwards to full backwards multiple times within a few seconds.

With a full traction wheel arrangement, it is much easier to induce these faults.

[apalrd]

We were able to repetitively fault out the Jaguars on our Lunacy shooter. Part of the spin-up process backed up the shooter wheel and feed conveyor (to get any moon rocks out of it), stopped the feed conveyor, spun up the drum, then fed the conveyor forward. This reverse/forward slam of a 6" diameter 24" long drum geared like 5:1 off a CIM was enough to fault the Jaguars on a battery that wasn't fully charged (e.g. 5 minutes into a demo, it would fail). If we had significant load on the drivetrain (any non-lunacy wheel), this time would have been very very short.

We haven't used Jaguars since the grey ones. We blew up quite a few that year, and combined with the overactive faults, were turned away.

That said, I have heard that the new black ones don't blow up as much as the grey ones.

[Ether]

http://www.chiefdelphi.com/forums/sh...92&postcount=4

http://www.chiefdelphi.com/forums/sh...2&postcount=43

[Andrew Schreiber]

Originally Posted by Ether

http://www.chiefdelphi.com/forums/sh...92&postcount=4

http://www.chiefdelphi.com/forums/sh...2&postcount=43

Context? What is this in response to?