Victors verses Jaguars?

[Greg Shaw]

I am a mentor for team 3601--a rookie team from Webberville Michigan. I was wondering if anyone can give me a pro/con list for Victors verses Jaguars. We chose jaguars for our drivetrain simply because the kit of parts came with more jaguars than victors. Specifically we had 4 jaguars and our drivetrain used 2 jaguars--this meant that we had 2 backup jaguars. For the chain tower that we built to hang tubes we used a victor.

Recently we had a 2 hour driving session with our robot--it had been a while since our last competition and our students wanted to use the robot. It turns out that 2 hours of continuos use puts alot of stress on CIM motors (lesson learned). We ended up burning out one of our CIM motors. When we fired the robot up the next day, I was surprised to dicover that it shut down the rest of the robot. I had expected the rest of the robot to work fine. I am wondering if this is a function of using a jaguar--it is my understanding that jaguars send info back to the lap top in a different way than victors. Would things had gone differently if we had used a victor? I understand that the simple fix is to replace the broken CIM motor--I am just trying to figure out how the system works so I can make educated decisions about speed controllers on future robots.

[RyanN]

First off, there have been a couple of recent threads about this, so while you're waiting for others to reply, you might try a search.

I'm going to make the assumption that your team used PWM cables (most teams use PWM for controlling Jaguar speed controllers) There is just a 1-way data flow, and that's from the Compact RIO (or digital side car (DSC), depending on how technical you want to get) to the speed controller of your choice with PWM control.

PWM, or Pulse Width Modulation sends a square wave over the signal (typically white wire) to the speed controller. The black wire is the negative, and the red wire is 6V positive (from the DSC PWM outputs). Another note to make is that the 6V positive is normally disabled unless you have the jumper in place to use the 6V line (usually only needed with servos).

So...
White - Signal, PWM Square Wave Signal
Red - Positive, 6V+ (normally disabled and open)
Black - Negative, 0V reference
1 way communication from Compact RIO to Speed Controller

So now that I have that cleared up, now on to Jaguars vs. Victors

Jaguars:
Pros:

• More linear control
• Better protected
• Quieter (fan noise)
• Quieter (motor control whine)
• Over-current protection
• Over-temperature protection
• CAN-bus (more on this in a bit)
• Cheaper

Cons:

• Large, weird shape
• Over-zealous over-current protection (trips too quickly)
• Defects (especially with Gray Jaguars [NO LONGER PRODUCED])

Victors:
Pros:

• Small
• Reliable (with care)
• CIMple (Just the basics, power, motor output, and PWM-in)
• Tried and trusted for many years (884 since I believe 2004, correct me if needed, and 883 before)

Cons:

• More expensive
• Open air design is prone to magically attracting the metal shavings
• No CAN-bus support
• No Over-Current Protection
• No Over-Temperature Protection
• Non-linear control curve

My opinion:
For drive motors, you can just stick with Victors. They'll be able to better provide the pushing power needed for those brief instances when you need it, and the auto-resetting snap action breakers will take care of the over-current problem. They're smaller, the fans run constantly, and there is less to go wrong inside of them.

For high-precision control, I would use Jaguars. The better linear control, plus the support for the CAN-bus will ultimately let you have better control of the motor. By high-precision, I speak of any motor used in a closed-loop control scheme with a sensor. There is nothing wrong with using them for the drive motors, and your team may want to use them for drive motors to have better control if using sensors such as the gyro or encoders for precise positioning.

We had cut-out problems with the Black Jaguars at the Championship this year. We believe it was just over-current protection on the field as we discovered we could trip the Jaguars if it came into a pushing match in high gear. No design flaw with the Jaguars or the robot, just a design limitation.

The CAN-bus is something your team may want to look into in the near future . It allows for 2-way communication, just like you mentioned. It offers some neat features for motor control too. You can control it like normal from 0-100%, current mode, voltage mode, faults, and more. It also allows you to get data from the Jaguars including temperature, voltage in, voltage out, and current. The programming will be a bit more complicated, and you will add a single point of failure to the robot. If you're willing to live with that, then use it. The single point of failure is the CAN-network itself. Instead of having a cable go to each speed controller in a star network configuration, you'll be using a piggy-back network, where there is only one control line, then a connection between each Jaguar with a termination connector on the last node (basically just a resistor between two pins).

Hopefully this will help you. Could you be a little more descriptive about what you mean the the rest of the robot shut down? What is working, what is not working?

[Ether]

Originally Posted by RyanN

Jaguars vs. Victors

Jaguars:
Pros:

• More linear control
• Better protected
• Quieter (fan noise)
• Quieter (motor control whine)
• Over-current protection
• Over-temperature protection
• CAN-bus (more on this in a bit)
• Cheaper

One thing I never see mentioned in these Jag vs Vic threads is the theoretical advantage that Jags produce less heat in the motor for a given motor torque. I've never had the opportunity to actually measure this; I was wondering if anyone has done so.

[pfreivald]

Jag Con: Fail randomly every time we use them.
Vic Pro: Don't.

[Ether]

Originally Posted by Ether

One thing I never see mentioned in these Jag vs Vic threads is the theoretical advantage that Jags produce less heat in the motor for a given motor torque. I've never had the opportunity to actually measure this; I was wondering if anyone has done so.

FWIW, anecdotal: I just had a report from a team that replaced Jags with Vics, and the motors are now running noticeably hotter.

[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.