Jaguars failing

[jhersh]

Originally Posted by Dave Flowerday

Joe's post above indicated that at least some failures were because of shavings when someone fully backed out the terminal screws. Ultimately this may be considered user-induced, but given that the black Jag was redesigned to eliminate this problem I'd say that it is at least partially due to a misunderstood requirement or design defect. If enough people are doing something that they thought was logical that ends up ruining the product, I usually consider that a design shortcoming.

This was actually considered a design enhancement originally. The idea was if the screws are painted a color code, then it will be LESS likely that teams will accidentally wire them up backward and set fire to them. But what if a team fully removes the screws and replaces them in the wrong place... then the color code is misleading. Ok... make the screws retained so that they won't be easily removed all the way, thus helping to ensure the color code stays correct.

After a year of teams overpowering the retention, TI must have decided that if teams are going to take them out anyway, the may as well not have metal shavings inside on top of the possible bad color coding.

Essentially, what was intended to help teams, only hurt them more since they didn't follow instructions.

[Joe Ross]

Originally Posted by jhersh

After a year of teams overpowering the retention, TI must have decided that if teams are going to take them out anyway, the may as well not have metal shavings inside on top of the possible bad color coding.

Essentially, what was intended to help teams, only hurt them more since they didn't follow instructions.

Perhaps the problem is that it isn't in the instructions (even now).

[skimoose]

Originally Posted by jhersh

This was actually considered a design enhancement originally. The idea was if the screws are painted a color code, then it will be LESS likely that teams will accidentally wire them up backward and set fire to them. But what if a team fully removes the screws and replaces them in the wrong place... then the color code is misleading. Ok... make the screws retained so that they won't be easily removed all the way, thus helping to ensure the color code stays correct.

After a year of teams overpowering the retention, TI must have decided that if teams are going to take them out anyway, the may as well not have metal shavings inside on top of the possible bad color coding.

Essentially, what was intended to help teams, only hurt them more since they didn't follow instructions.

I wouldn't have considered this a design enhancement. I've always considered ring connectors to be much safer than fork connectors. A loose terminal screw will not result in a stray wire loose in a robot frame.

Also, weren't ring terminals given in the KOP? How do you get a ring terminal onto a screw without backing the screw completely out? We had zero burned out Jaguars last year and we backed out all of our screws to use ring terminals. I suspect the issue is something else.

Reverse polarity on the line side is the quickest way to smoke a speed controller, so why not place color coding on the case so that when careless people remove the screws they get back in the correct positions? Also, while the case on the Jaguars is much more user friendly at preventing metal filings getting where they shouldn't, it's not fool-proof. Many teams claim they're careful about metal filings, but I can't count the number of times I've witness teams drilling, filing, grinding, or cutting (Dremel cutoff wheels are a big one) over vital electronics with no cover to catch flying chips and dust. They don't see any metal chips or filings, but there is conductive dust from the cutoff wheels everywhere.

[jhersh]

Originally Posted by skimoose

Also, weren't ring terminals given in the KOP? How do you get a ring terminal onto a screw without backing the screw completely out?

We always use wire cutters to snip a little slot out of the ring right by the wire connection resulting is a hook. Much easier to wire and similar protection against loose connections.

Originally Posted by skimoose

We had zero burned out Jaguars last year and we backed out all of our screws to use ring terminals. I suspect the issue is something else.

Shavings inside aren't a guarantee of failure, it just makes it likely. If I were you, I would open up all of them and clean them out thoroughly. I'm not sure what the most appropriate way is... perhaps an air duster. You can probably get advice from TI. I wouldn't use them until they were cleaned though.

[jhersh]

Originally Posted by Joe Ross

Perhaps the problem is that it isn't in the instructions (even now).

Oops. Perhaps someone should let TI know about this.

[Al Skierkiewicz]

Joe,
If a Jag was opened and metallic dust found inside, I think a vacuum is more appropriate. Compressed air will force some of the dust between or under the pins of surface mount components and under the shroud that surrounds the FETs. Many teams do not realize how much metallic dust is actually generated right on their robot. Open gears and sprocket/chain interfaces for instance throw a lot of fine metal dust while they wear. The big offenders are rotating or moving parts that rub against robot frames. i.e. arm attachments, shafts with no bearings, etc.

[Tom Line]

Originally Posted by jhersh

The way to tell is by plugging it into CAN. If using a black jag as a bridge, you can use the bdc-comm utility to query the version. If you intend to use the Servo PWM interface, then you don't need to upgrade the firmware.

As for hardware revisions, they are either black or gray plastics. All gray jags are the same hardware inside.

Thanks Joe! Unfotunately I'm working afternoons and midnights right now. Getting home at 4am is killin' me, and putting a crimp on responding to chief delphi questions in a quick manner is a bit tough.

[Peter Randall]

It has started again. We have already toasted two Jags from last year. We purchased a number for last year's bot and removed them all from the robot after toasting 4. We just built a prototype drive base and in two days have smoked 2 of the "replacements" we got last year. Same symptom, it only loses one direction after issuing the magic smoke. I really wanted to move to CAN, but I CAN'T if I CAN'T rely on the Jags. Has anyone smoked a Black Jag yet???

PGR

[Tom Line]

Originally Posted by Peter Randall

It has started again. We have already toasted two Jags from last year. We purchased a number for last year's bot and removed them all from the robot after toasting 4. We just built a prototype drive base and in two days have smoked 2 of the "replacements" we got last year. Same symptom, it only loses one direction after issuing the magic smoke. I really wanted to move to CAN, but I CAN'T if I CAN'T rely on the Jags. Has anyone smoked a Black Jag yet???

PGR

Peter, are you covering the open connectors on the jags with tape, a plastic jumper, or something else? It's been shown that direct static to the open jag connectors can cause issues.

Have you tested your frame to see if you're running electricity through it?

Are you mounting your electronics on a conductive or a non-conductive surface?

[Al Skierkiewicz]

Tom,
The direction failures are attributable to one of the power FET gate drivers shorting. I don't remember if the cause of the failures was ever found or reported.

[Chris_Elston]

We smoked our first Jag today. I was a bit surprise how it decided to go up in smoke.

We did not have any failures last year. This was a brand new one just out of the box. It was not under any stress, and decided to smoke. It's less than two days old. That's too bad because I am sure Luminary probably doesn't replace them because they assume you abused them. I hope we don't have any more that die like this one. It was almost in "coast mode" and poof...

[Joe Ross]

Originally Posted by Chris_Elston

That's too bad because I am sure Luminary probably doesn't replace them because they assume you abused them. I hope we don't have any more that die like this one. It was almost in "coast mode" and poof...

That seems like quite an unfortunate assumption to make considering that Luminary Micro's Failure Analysis Report states that Luminary Micro promptly replaced every failed Jaguar last year.

[Chris_Elston]

Thanks for this report.

Looks like ours is a U6/U7 failure.

[omalleyj]

Team 1279 worked on the Black Jag Beta program and we did manage to blow up two with static discharge, one by accident, and one on purpose (under TIs direction). Last years robots were very static prone, and the encoder and potentiometer inputs are fairly exposed. I would recommend covering the inputs with empty connectors when not using them to prevent that type of failure.

I would note that we also blew up our Kwik Byte driver station's ethernet connectors when running tethered at a fundraiser, so the Jaguars are not the only static sensitive devices. Use due care with all your sensors, etc..

TI was very good to work with about the failures, and they seem committed to improving their product. I would say that any team who has a failure should contact TI, document the conditions, and return the blown part. The Jags have many cool features and I would very much like to see them become a reliable component.

[Tom Line]

Originally Posted by Al Skierkiewicz

Tom,
The direction failures are attributable to one of the power FET gate drivers shorting. I don't remember if the cause of the failures was ever found or reported.

Al,

I stated that because there was some discussion previously regarding the static. I wasn't sure if it had been on the beta test boards or not, but the summarization was that static charge directly applied to the exposed terminals could create issues in the jags. I couldn't remember who said it (fortunately someone spoke up here).

We'll be using Jag's again this year on our practice robot. I'm interested in seeing how they behave. We used them last year on our sparring-partner in the drive train and never experienced any issues with, though I know that anecdotal evidence is really of no help in determining their reliability.

Tom