Jaguars vs Victors

[Joe Johnson]

As a suggestion, 1 CIM per side without a shifter and with anything approaching grippy wheels is probably going to be a stretch to keep from over working the CIM or the Jaguar (or Victor) or (most likely if you fix the other problems) the 40A Breaker.

I suggest you buy two CIM-Sim from AndyMark or a CIMULATOR from Banebots and use one of the excellent 550 motors that are legal (one of the many FP motors or Banebot 550 motor... -- in general the more power the better) and buy another two Jaguar or (better yet, given my GAH!!! in the message above) two Victors.

If you install this on your CIMPleBox in parallel with your CIM you will have more power to turn but more importantly in your case, you will have two current paths -- and since loses are an I^2 R problem, halving your current can effectively quarter your electrical heat dissipation.

And, as long as you can wire up the speed controllers & press the gears on at the competition , everything is COTS so it doesn't count on the 30lbs allowance (of course you still have to make your 120lbs limit but one battle at a time...)

Wishing us both luck...

Joe J.

[Cal578]

Originally Posted by Joe Johnson

...you will have two current paths -- and since loses are an I^2 R problem, halving your current can effectively quarter your electrical heat dissipation.

Formula is correct, application is almost correct.
The total current didn't get halved, it just got split into two paths. So, if everything else is the same, the power dissipated per path is a quarter of the original, but you have twice as many paths, so the total power dissipated (lost) is half the original (which is still a good thing).

To put it another way, putting another identical load in parallel with the first means your R is cut in half, which directly says that the power is cut in half.

Also, I just said "if everything else is the same", but if you're changing motors and/or gearing, then everything isn't the same. If new motors or gearing gives you a better match of motor to load, then that will be where you see the biggest improvement, and heat caused by losses becomes a smaller issue.

[Joe Johnson]

Originally Posted by Cal578

Formula is correct, application is almost correct.
The total current didn't get halved, it just got split into two paths. So, if everything else is the same, the power dissipated per path is a quarter of the original, but you have twice as many paths, so the total power dissipated (lost) is half the original (which is still a good thing).

To put it another way, putting another identical load in parallel with the first means your R is cut in half, which directly says that the power is cut in half.

Also, I just said "if everything else is the same", but if you're changing motors and/or gearing, then everything isn't the same. If new motors or gearing gives you a better match of motor to load, then that will be where you see the biggest improvement, and heat caused by losses becomes a smaller issue.

You are right, I was sloppy. But here is the thing. It is heat that ultimately kills the electronics. If you halve the current per leg, then that leg is going to see much less than half (~1/4 to first order) of the heat it would have otherwise seen.

So from a stress your electronics pov, it is a better than halving. That was my point, which I think is still valid.

Joe J.

[Cal578]

Originally Posted by Joe Johnson

It is heat that ultimately kills the electronics. If you halve the current per leg, then that leg is going to see much less than half (~1/4 to first order) of the heat it would have otherwise seen.

So from a stress your electronics pov, it is a better than halving. That was my point, which I think is still valid.

I agree, you are right on that point.

[enginerd]

Originally Posted by Joe Johnson

GAHHH!!!!

Jaguars are 4 years old now and they are still so fragile?

We are having fits with the Jaguars. I have been attributing them to some CAN related collateral damage but after reading this thread, I am starting to think that Jaguars are just not safe to use. Seriously.

Joe J.

We exclusively use victors. We gave them another chance last year, but they proved too unreliable. Ensure your mechanicals systems are designed and functioning correctly, but don't rule out the jags as the root of your problems.

Our students keep asking if they can recreate the office space copier scene with jaguars. After the pain they caused us, I'm reluctant to say no.

[Alex Chambers]

Originally Posted by slijin

A fried jaguar, which from the sounds of it was their problem, can't be fixed by magical firmware, no matter how much we want it to

He described red flashing lights, which suggest to me they may not be fried, usually when a jag is fried it does not have any led at all or the led will display correctly. however as i stated it may not be a gate fault its just that his description mirrored the problem i mentioned.

[Daniel_LaFleur]

Originally Posted by Joe Johnson

GAHHH!!!!

Jaguars are 4 years old now and they are still so fragile?

We are having fits with the Jaguars. I have been attributing them to some CAN related collateral damage but after reading this thread, I am starting to think that Jaguars are just not safe to use. Seriously.

I do not want my speed controllers "protecting" me by shutting themselves off. If they can't take the heat get the heck out of the FRC kitchen!

This is killing us.

I will have some choice words for FIRST Engineering after the season but man oh man has FIRST a lot of 'spainin' to do...

Joe J.

Dr Joe,

The Jags aren't as fragile as some put them out to be. Here in FIRST we tend to ABUSE speed controllers rather than use them.

That being said, there are a few areas where the Jags need to be made better:
1> CAN control -- The Can-bus and its related connectors tend to be ... touchy. A better positive lock and more robust pin setup would help things immensly.

2> Failure reporting -- The Jag has plenty of processing power. It needs to report exactly what the failure is, not just a flashing LED, so that our control system may deal with said failure.

3> For some reason the Jag seems to be a swarf magnet. Possibly adding a filter to the air intakes would help.

4> Protection from reverse power and reversed input/output. At least create connections that are physically different so that you cannot reverse input and outout wires ... and somehow protext from reversed input power (I havent looked at the schematic to determine an easy one here).

All this being said ... with proper care and feeding ... Jags are a good speed controller and they offer many benifits that the Victors do not.

[Matt Krass]

Originally Posted by Daniel_LaFleur

Dr Joe,

The Jags aren't as fragile as some put them out to be. Here in FIRST we tend to ABUSE speed controllers rather than use them.

That being said, there are a few areas where the Jags need to be made better:
1> CAN control -- The Can-bus and its related connectors tend to be ... touchy. A better positive lock and more robust pin setup would help things immensly.

2> Failure reporting -- The Jag has plenty of processing power. It needs to report exactly what the failure is, not just a flashing LED, so that our control system may deal with said failure.

3> For some reason the Jag seems to be a swarf magnet. Possibly adding a filter to the air intakes would help.

4> Protection from reverse power and reversed input/output. At least create connections that are physically different so that you cannot reverse input and outout wires ... and somehow protext from reversed input power (I havent looked at the schematic to determine an easy one here).

All this being said ... with proper care and feeding ... Jags are a good speed controller and they offer many benifits that the Victors do not.

As I stated earlier, I tend to agree that the Jaguars are not well suited to our uses. I find their over-current protection to be overly touchy, but not so touchy that I would dismiss repeated shutdowns without at least analyzing the performance of the system.

In general I don't like my electronics 'helping me' unless I specifically ask them to, including a fixed, sensitive over-current shutdown. As a feature I think it's excellent, but it should be configurable, or at least something that can be enabled or disabled by jumper/CAN.

In my (bad) experience, the Jaguars are no more swarf loving than Victors, and I mean that in that our Victors tend to blow up from swarf (I'm really amused by that word) as often as our Jags. In general I think teams might just be getting worse about swarfing (seriously, it's fun to say) around the controllers.

I would like to see a variety of improvements to the CAN system, including better failure reporting, and an internal software switchable terminator, or even just a jumper we could put in place on the Jag(s) at the end of the line to terminate it. I actually don't have much a problem with the existing physical interface, other than that I seem to have a terrible track record with crimping.

Reverse power protection is a pet project of many people, even I'm toying with it, it's really difficult problem given the currents and voltage we're dealing with here.

Bottom line, the Jags have potential, and we do use them primarily for drive systems (because of the internal encoder support -- which I'm on the fence about) but that is all, I find they are not as robust as Victors, and I find they are not sufficiently polished... yet, but they're rapidly getting there. I think a lot of their 'great features' are as of yet under developed and are more novelty than useful tool.

Also, swarf. Swarfing swarf. (Really, try to say it out loud with a straight face)

Matt

[enginerd]

Originally Posted by Joe Johnson

GAHHH!!!!

Jaguars are 4 years old now and they are still so fragile?

We are having fits with the Jaguars. I have been attributing them to some CAN related collateral damage but after reading this thread, I am starting to think that Jaguars are just not safe to use. Seriously.

Joe J.

We exclusively use victors. We gave them another chance last year, but they proved too unreliable. Ensure your mechanicals systems are designed and functioning correctly, but don't rule out the jags as the root of your problems.

Our students keep asking if they can recreate the office space copier scene with jaguars. After the pain they caused us, I'm reluctant to say no.

[Levansic]

I don't understand all of the negative feelings about the Jaguars, vs. the Victors. The Jaguars are very adequate for a properly designed electromechanical system. If the jaguars are too "weak", then you're doing it wrong.

Seriously, we often loose sight of the forest from the trees. It is a natural tendency to grasp absolute numbers and attempt to achieve superlative performance. Because of this, many robots in FRC tend to be way under geared, chasing mythical top speeds that our calculations say we should hit. The results are sluggish robots that heat up their immediate surroundings and depleting batteries, motors, and motor controllers at an astounding rate.

Acceleration, not speed is what improves the drive performance. The field is not big enough for a bogged down robot to ever hit top speed. Double or tripple your gear ratio, and the power draw drops significantly. At the same time, your robot will get significantly faster and it will be far more responsive.

In the past, I have seen ~50% increases in gear ratio actually increase a good robot's top speed by ~30%, while improving battery life. Last year, we increased our gear ratio by 120%, and went from constant brown-outs and slow movement to a moderately fast robot that was quite maneuverable. We had other glitches, but the jaguars were not the problem.

[dsirovica]

Great discussion - to sum it up:

1. Jags may be overprotective of the system causing most FIRST teams to opt for Victors (though probably for the wrong reasons) - solution: get TI to allow a mode of "reckless" on the Jags to account for short bursts of activity in the "danger zone" like a 2.5 minute competition.

2. Gearing down seems to be the most recommended solution.

A related Q: we found that when a Jag stalls at full power it will cut out and also crash the cRio - have others had that experience?

Dean

[slijin]

Originally Posted by Levansic

I don't understand all of the negative feelings about the Jaguars, vs. the Victors. The Jaguars are very adequate for a properly designed electromechanical system. If the jaguars are too "weak", then you're doing it wrong.

A properly designed electromechanical system, yes, but let's face it - how many of us really get a chance to properly design and iron out every kink of our robot? The fact that designs need to iterated and constantly improved forces us to abuse our robots and consequently crash the Jaguars.

That being said, there are numerous reasons - somewhat attributable to poor design - that Jaguars are considered less robust than Victors. Their 40A overcurrent protection, for instance, may be a nice safety feature, but it's a frequent source of frustration for teams who find that their application may occasionally necessitate current spikes above 40A. Quality control on the physical RJ11 and RJ12 jacks has also been documented to be subpar. CAN issues - both on the electrical and software sides - have been linked to fundamental limitations of and problems with the involved hardware that aren't made explicit to users.

Long story short, it isn't just poor design that generated the "Victors for reliability, Jaguars for features" mantra.

Originally Posted by dsirovica

A related Q: we found that when a Jag stalls at full power it will cut out and also crash the cRio - have others had that experience?

That's extraordinarily unlikely. If anything, the Jaguar's built in overcurrent protection should be preventing such a crash. The 24V power supply can handle voltage dips to 4.5V. If your battery voltage is low enough for one 40A draw to sink it below that level, then you need a new battery.

[dsirovica]

Originally Posted by slijin

That's extraordinarily unlikely. If anything, the Jaguar's built in overcurrent protection should be preventing such a crash. The 24V power supply can handle voltage dips to 4.5V. If your battery voltage is low enough for one 40A draw to sink it below that level, then you need a new battery.

Sorry I don't know how to add a link to a post , but there are test results posted under
CD>technical>programming>Voltage vs. PercentVbus

In there you will see that the Jags do not cut out at 40A precicely - I believe it is a thermal mechanism. We were getting 100A+ spikes and 80A+ for many seconds before cut out. You will also see a very minimalistic settup and the cRIO crashes consistently -see CIM Test #6 & 7

In the same thread a contributor who appears to be from NI says the 8 slot cRIO (which ours is) needs 19V to work. We did not test that.

So far no one else has responded that they too had cRIO crashes when CIMs stall, so it may be something with our PDB it is an old war scarred PDB so will do more tests and report back when we recover from the post bagging depression

[slijin]

Originally Posted by dsirovica

Sorry I don't know how to add a link to a post , but there are test results posted under
CD>technical>programming>Voltage vs. PercentVbus

I've been following this thread, actually; I just haven't been reading very thoroughly as I've had work to do. To link to a post, just right-click the post #, which is at the top right corner of a post.

Originally Posted by dsirovica

In there you will see that the Jags do not cut out at 40A precicely - I believe it is a thermal mechanism. We were getting 100A+ spikes and 80A+ for many seconds before cut out. You will also see a very minimalistic settup and the cRIO crashes consistently -see CIM Test #6 & 7

To my knowledge, this cutout is done by the firmware, not by a thermal mechanism. The Jaguar actually monitors the current. It is, however, designed to handle above 40A for a few seconds; speculating on the reason for the "many seconds" is beyond me.

Originally Posted by dsirovica

In the same thread a contributor who appears to be from NI says the 8 slot cRIO (which ours is) needs 19V to work. We did not test that.

So far no one else has responded that they too had cRIO crashes when CIMs stall, so it may be something with our PDB it is an old war scarred PDB so will do more tests and report back when we recover from the post bagging depression

Both the 2011 and 2012 PDBs are designed to output 24V down to a 4.5V input; I'm not aware of specs for the 2009 or 2010 PDB.

We managed to reboot our cRIO once, but we managed to push our robot to cause a current spike that forced our voltage to around 4V, so I'm not surprised that it happened.

[enginerd]

Originally Posted by Joe Johnson

GAHHH!!!!

Jaguars are 4 years old now and they are still so fragile?

We are having fits with the Jaguars. I have been attributing them to some CAN related collateral damage but after reading this thread, I am starting to think that Jaguars are just not safe to use. Seriously.

Joe J.

We exclusively use victors. We gave them another chance last year, but they proved too unreliable. Ensure your mechanicals systems are designed and functioning correctly, but don't rule out the jags as the root of your problems.

Our students keep asking if they can recreate the office space copier scene with jaguars. After the pain they caused us, I'm reluctant to say no.