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Unread 02-24-2012, 10:36 AM
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Jaguars vs Victors

Our drive system uses only 2 CIM motors (we are using the other 2 CIMs on our shooter and ball pick up mechanism). All motors (5) are using Jaguar speed controllers.

On our 1st test drive everything was working pretty well, though I did notice it was not easy to rotate the (6-wheel drive) robot. It was necessary to get a bit of movement forward or back before turning was possible.

After some more work, our 2nd test session ended with both drive jaguars showing slow-flashing red.

My theory is that the jaguars were damaged by pushing the unpowered robot around on its wheels with the jaguars still connected. Team members report seeing the lights on the jaguars lighting up while they were pushing it around.

Anyhow, it's all bagged up now, but I need to figure out what to do when we get to the competition. I think the next step to correct the problem is to swap out the speed controllers. Hopefully that will fix it.

We don't have any more jaguars, but we have a bunch of victors.

We're not using CAN bus, or any special jaguar features.

So... should we rearrange so that we have jaguars on the drive, or just put victors in for the (presumed) damaged jaguars?

Also, is my theory of how the jaguars were damaged a reasonable or probable one?
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Unread 02-24-2012, 10:46 AM
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Re: Jaguars vs Victors

It sounds to me like your drive system draws a lot of current when attempting to turn. As you wear down the battery, this is more and more likely to throw the Jaguars into a low-voltage fault protection (indicated by the flashing red).

I would guess that the Jaguars are not damaged. Many teams roll un-powered robots around like this. You will see enough power back-fed into the system to light up the Jaguar LEDs, but in my experience it is difficult if not impossible to back-feed enough voltage/current to damage things.

The potential solution(s) would be make your robot easier to turn by reducing friction on one or more sets of wheels, reduce the current draw by increasing the gear reduction (less speed more torque) or if the system works OK for 2.5 minutes of driving on a fully charged battery, be prepared to swap batteries every match.
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Unread 02-24-2012, 10:49 AM
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Re: Jaguars vs Victors

It sounds like the drive train gearing & traction/turning friction are too high.
The red flashing means that the Jaguars are sustaining over-current and shutting down to protect themselves.

It isn't related to pushing the robot around and getting back EMF to light up the Jags. You really don't see much power that way.
It's the CIMs operating at stall (133amps) for too long, and the Jags clamping down on that.

Victors will improve the situation somewhat as they have more tolerance for stalled CIMs, but you may want to consider either dropping the middle wheels more, or changing the sprockets to gear the drive train down.
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Unread 02-24-2012, 10:49 AM
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Re: Jaguars vs Victors

Quote:
Originally Posted by tux View Post
Our drive system uses only 2 CIM motors ... it was not easy to rotate the (6-wheel drive) robot.
What gear ratio are you using? Hopefully not just CIMple boxes with no downstream sprocket reduction.

Are you using pneumatic wheels by any chance?

Some teams have reported that 1/8" center drop is not sufficient for pneumatic wheels.


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Unread 02-24-2012, 11:34 AM
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Re: Jaguars vs Victors

Thanks for all the replies!


Quote:
Originally Posted by Ether View Post
What gear ratio are you using? Hopefully not just CIMple boxes with no downstream sprocket reduction.
I don't know exactly. It is the CIMple gearboxes, but those drive small pinions and in turn chains and a set of larger sprocket gears at each wheel.

I had mentioned the possible need to go with larger sprockets, but the team did not look happy at that prospect. I still think it may be needed....


Quote:
Originally Posted by Ether View Post
Are you using pneumatic wheels by any chance?
No.

Quote:
Originally Posted by Ether View Post
Some teams have reported that 1/8" center drop is not sufficient for pneumatic wheels.
I hadn't though of that. On a hard surface it turned very easily, but the test drive was our first time on any sort of carpet. I'm not sure how much work it will be to drop those center wheels down more.

If our wheels are not air-filled, that is not likely to help?


The strange thing is that it was driving around pretty well just the day before... On the 2nd test drive it started out Ok, but then after trying to go over the ramp once, all we could get was flashing red. We tried a fresh battery, but it was all the same, even just trying to move straight forward.


One thing the Jaguar FAQ mentioned is a too-tight chain. I remember working pretty hard to get those chains on. How much of a factor might that be?
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Unread 02-24-2012, 12:03 PM
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Re: Jaguars vs Victors

Quote:
Originally Posted by tux View Post
I hadn't though of that. On a hard surface it turned very easily, but the test drive was our first time on any sort of carpet. I'm not sure how much work it will be to drop those center wheels down more.

If our wheels are not air-filled, that is not likely to help?
Dropping the center wheels further will help greatly, if that is the problem. Of course, too much drop and you'll have a bot that rocks back and forth.

Quote:
One thing the Jaguar FAQ mentioned is a too-tight chain. I remember working pretty hard to get those chains on. How much of a factor might that be?
If the chain is so tight that it doesn't budge at all when you try to wiggle it, it is too tight. Tight chains add friction.


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Unread 02-24-2012, 07:26 PM
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Re: Jaguars vs Victors

I'd just like to point out something about this situation.

First, let me be upfront and say I'm not the biggest fan of Jaguars, I prefer Victors because I find them simpler, smaller and generally more robust. I also find that they can take more roughhousing than the Jaguars, which give up somewhat easily in my opinion.

That said, your Jaguars are trying to tell you something, if your system is constantly going in to fault mode and shutting down, your solution should not ever involve getting rid of the device that is shutting you down in favor of one that will ride things out until the (bitter) end. It is faulting out for some reason and you should stop to think about what reason that is. Perhaps the Jaguars are giving up too easily, but I suspect (as others have suggested earlier) you have a legitimate problem.

Bottom line, if your robot is complaining a lot, it might just be whining, or it might be warning you about a problem before it's too late!

I think you've already learned this lesson, but I just wanted to reinforce it.
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Unread 02-24-2012, 07:48 PM
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Re: Jaguars vs Victors

Could it be that the output wires shorted together when the robot went over the bridge?
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Unread 02-24-2012, 08:13 PM
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Re: Jaguars vs Victors

Quote:
Originally Posted by Kevin Selavko View Post
Could it be that the output wires shorted together when the robot went over the bridge?
That should not be possible if everything is properly hooked up and insulated; the wires should be insulated right up to the point where they meet the Jaguars making shorting impossible. With other motors, This is more likely since unshielded female spade connectors can shake loose and come into contact, but these shouldn't be needed with CIMs
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Unread 02-24-2012, 08:50 PM
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Re: Jaguars vs Victors

Our team has had a similar problem it could be due to
1) The chains being to tight on your drive train
2) The motors trying to do too much work on the robot and the jaguars are resetting themselves
3) Your gear ratio on your drive train is geared to low and you need more torque
4) Your robot might be too heavy

Solutions:
1) Loosen chains on your robots (unless your not using chains)
2) Use a larger guage wire on you robot and jaguars
3) Change the gear ratio going from small to large
4) Loose weight (I suggest weight watcher )
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Unread 02-25-2012, 10:33 AM
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Re: Jaguars vs Victors

Quote:
your Jaguars are trying to tell you something, if your system is constantly going in to fault mode and shutting down, your solution should not ever involve getting rid of the device that is shutting you down in favor of one that will ride things out until the (bitter) end. It is faulting out for some reason and you should stop to think about what reason that is. Perhaps the Jaguars are giving up too easily, but I suspect (as others have suggested earlier) you have a legitimate problem.
^^^ Quoted for truth. If time and resources permit, find the root cause of the problem and fix it.

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Unread 02-25-2012, 12:35 PM
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Re: Jaguars vs Victors

Im not sure why your getting this error but if it makes the jags not work on other systems this might help you to get them running again.I helped fix a similar problem for another team through firmware this year. Their robot encountered the problem when running two cims and using pwn were their jaguars acquired flashing red lights and would not function. I was able to fix their problem using the bdc-com updating tool that the jaguars use for firm ware. to do this:

1.install bdc com on your computer (you can find it on texas instruments sight somewhere)
2.install black jaguir firm ware (i assume your using black jags, if your not you have to make a can connection between the jags)
3.use a db9 to rj11(phone line) cable and connect your computer into the correct can port on the jag,
4.you need a terminator plug so either borrow one at regional s or solder a resistor between the green and red wires on on some phone line then put that into an rj11 crimp
4.5.plug this into your jaguir
5.go to bdc com and see if in the upper right hand corner you get an error called gate fault.
6.if you do have a gate fault reset the jaguar to factory default
7.install black jag 101.bin on your jag
8.it should be unbricked. and the red light should go away
9.if you get the error "cannot access the boot loader" you have to use the reset button to manually factory reset the jag. then use black jag 101.bin on the jag.

Im not 100% certain how the gate fault error happens, i was not there to see this team break their stuff. But by messing with the jaguars firmware through a can to computer serial port hookup i was able to make it work for them again.

or you could just switch to victors, easier solution

-note if you don't have the gate fault error im not sure if the firmware reset will help you.

Last edited by Alex Chambers : 02-25-2012 at 12:37 PM.
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Unread 02-25-2012, 01:04 PM
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Re: Jaguars vs Victors

Quote:
Originally Posted by Alex Chambers View Post
Im not sure why your getting this error but if it makes the jags not work on other systems this might help you to get them running again.
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
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Unread 02-25-2012, 01:04 PM
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Re: Jaguars vs Victors

We have abandoned Jags in favor of Victors two days before bag-day!
Apparently this is a yearly tradition on our team

We also started with 6 wheels, 2 CIMs on CIMple boxes and had friction issues on carpet. Covering wheels with duct tape worked but not cool, so we eventually lost the midddle wheels. The Jags kept cutting out, the Victors don't.

Jags have 2 MOSFETs per H-Bridge link, Victors have 3, and I don't think Victors have a cuttout like the Jags.

I agree with prior comments that this is NOT the way to solve this problem as Jags (one assumes are designed corrctly...) are cutting out for safety reason. As a result we can "fry an egg on the CIMs"! and we can barely make it through a match on one battery.

Turning from standstill is the biggest current drain - 90A per CIM!
Moving first helps a lot.

I suspect that 2 CIMs is simply too weak for a 120lb bot. Gearing down would be the best solution for us, however its bagged...
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Unread 02-25-2012, 02:41 PM
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Re: Jaguars vs Victors

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...

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