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Unread 21-01-2013, 17:53
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Interesting Jaguar Death

Today, whilst doing drive train testing I noticed one wheel was not spinning. Went and checked the jaguars and found the jag controlling that wheel to be off. No light, no smoke. Upon closer examination, the jaguar was emitting a distinct "tick", and each "tick", the fan would twitch. The jag "ticked" about once per second. I also noticed that the positive motor terminal had melted the plastic surrounding it. The robot was only under a moderate load.

Language: Java
Controller: Black Jaguar (PWM) 2012 KOP model.
DriveTrain: Direct Drive

Any Ideas?
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Unread 21-01-2013, 17:59
nighterfighter nighterfighter is offline
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Re: Interesting Jaguar Death

Is it possible some metal fell and shorted the leads?
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Unread 21-01-2013, 18:01
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Re: Interesting Jaguar Death

It's highly unlikely, the control board is wood, and they had covers up until we started testing them. I also did not see anything in it when i had it open, or any scorching on the pcb.
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Unread 21-01-2013, 18:02
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Re: Interesting Jaguar Death

Although I am not for sure, the ticking you may be hearing is the Jags built-in overload thermal reset. Check your supplied current and make sure it falls within the specs of the jag!
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Unread 21-01-2013, 18:07
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Re: Interesting Jaguar Death

The jag was on a 40 amp snap action breaker, and none of the wires felt hot. We let the jag sit for about 15 minutes and tested it again, same thing, tick and twitch.
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Unread 21-01-2013, 18:15
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Re: Interesting Jaguar Death

Quote:
Originally Posted by jp1247 View Post
Today, whilst doing drive train testing I noticed one wheel was not spinning. Went and checked the jaguars and found the jag controlling that wheel to be off. No light, no smoke. Upon closer examination, the jaguar was emitting a distinct "tick", and each "tick", the fan would twitch. The jag "ticked" about once per second. I also noticed that the positive motor terminal had melted the plastic surrounding it. The robot was only under a moderate load.

Language: Java
Controller: Black Jaguar (PWM) 2012 KOP model.
DriveTrain: Direct Drive

Any Ideas?
What do you mean by Direct Drive; motor directly connected to the wheel?

Did you notice it going into the Current Fault mode (Blinking amber-red with at couple second cutout) when you were driving around?

Please post more details like what motor you were using, gear ratios, etc.

Carefully unscrew the case and open up the Jaguar and look for any more visible damage. Pop out the PCB gently. The fan cable is connected via a connector and you risk breaking the fan if you aren't careful.

You may also want to take a look at the Jaguar FAQ. It lists some common symptoms and what their common issue/fix is. I'm not saying that the FAQ has your exact failure mode, but you may recognize some symptoms and that can help pinpoint the cause.

-David
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Unread 21-01-2013, 18:20
dyanoshak dyanoshak is offline
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Re: Interesting Jaguar Death

Quote:
Originally Posted by Lightfoot26 View Post
Although I am not for sure, the ticking you may be hearing is the Jags built-in overload thermal reset. Check your supplied current and make sure it falls within the specs of the jag!
The Jaguars do not have an internal thermal breaker. The Jag firmware monitors the current and shuts off the output if it gets too high for too long.
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Unread 21-01-2013, 18:27
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Re: Interesting Jaguar Death

The FAQ had nothing... As for gear ratio, I don't know. It is a single CIM into a toughbox circa ?2010-2011? The wheel spins easily without the motor, no problem there, and with the motor it feels just like the rest of the wheels. The jag never went into thermal/over-current protection, it just turned off. I've had the jaguar apart, no aluminum chaff in it, no bridged traces, no scorch marks on the pcb. All of the MOSFETs look normal. I unplugged the fan to find if it was the source of the clicking, which it was not.

I almost think it's trying to boot, but cant, since the fan twitches.
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Unread 21-01-2013, 19:54
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Re: Interesting Jaguar Death

The periodic twitch could be the Power Distribution Board's circuit breaker resetting and immediately cutting off again. I remember seeing symptoms something like that when the motor controller was wired with power directly to its motor outputs; might that be the case here?
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Unread 21-01-2013, 20:13
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Re: Interesting Jaguar Death

Originally that's what i though too, but no red light on PD, or breaker resetting. Also, don't hate on me, but i did use a Anderson plug straight from the battery to test it, same symptoms...
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Unread 21-01-2013, 20:15
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Re: Interesting Jaguar Death

What happens if you remove the load from the Jaguar?

If you have access to a oscilloscope, if not try a multimeter and put one lead on the 12V input, do you see anything abnormal?

Verify that the PWM cable works and is plugged in properly.


I recall an issue slightly similar to this on a tan jaguar while using CAN. What would happen was the jaguar would turn on and would flash yellow once and turn off for around 2 seconds then flash again. If I tried to drive it at all the status light would stay off indefinitely. I reflashed the firmware but the issue remained. I reflashed the bootloader ad the firmware (through JTAG in the back) and it worked fine after that. I have a full firmware dump on my other computer somewhere.
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Unread 21-01-2013, 20:17
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Re: Interesting Jaguar Death

Same symptoms with no load. I will have an oscilloscope next Saturday... But I don't even get one flash out of it, just a tick and a twitch.
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Unread 22-01-2013, 13:41
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Re: Interesting Jaguar Death

jp,
The fan is controlled by the micro proc and it in turn is powered by a series of regulators. I would remove the motor leads from the jag and then inspect for damage to the screw terminal. If the plastic is melted, it is likely that the two output terminals are shorted together. Since the Jag uses a bootstrap power supply, the output is always jumping to full output for a short period of time. I bet the symptoms are: power up, regulators come up and fan starts to spin, short on output shorts out during the bootstrap and the Jag senses the loss as a power loss and starts the sequence all over again.
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Unread 22-01-2013, 18:39
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Re: Interesting Jaguar Death

It took me a while to remember, but I have seen these symptoms before.

When there is a short on the 5V rail inside the Jaguar the 5V DC/DC converter can't come up. It tries to turn on, but it quickly shuts off due to its over-current shutoff. This shutoff is inside the DC/DC converter and has nothing to do with the software current limit in the Jaguar firmware. After the shutoff time is over, the converter tries to power on again, repeating the whole process.

The clicking you hear is the inductor changing shape due to magnetostriction* every time the converter tries to turn on.

The fan is powered by the 5V rail so it twitches at the same period as the shutdown time.

Many things can cause a short on the 5V rail, but one in particular stays even after you disconnect all the wires and clean out the debris from your Jaguar.

There are several ESD suppression diodes connected to the sensor inputs on the front of the Jaguar (added after Grey Jag and Lunacy ). If one of the pins experiences a static shock, it shunts the discharge to ground and hopefully protects the microcontroller. The diodes can handle high voltage (several kV) for a short amount of time, but if they experience a much smaller voltage for a longer amount of time (6V for these diodes in particular), they can fail in the worst way possible; short-circuit. There is one diode in particular that is connected to the 5V rail and if it fails, you now have a short from 5V to ground.

So, what can cause this diode to see more than 6V? Debris is one way. It is definitely possible that a piece of debris bridged 5V and some higher voltage rail.

I'm not sure where the melted motor terminal plastic fits in to the story. It may not even be related to the failure.

You mention this Jaguar was from the 2012 KOP. You seem to have debris under control this year, but can you guarantee that debris wasn't introduced last year? Was this Jaguar tested and guaranteed working right before adding it to your 2013 chassis and noticing the failure?

-David

*Thanks EricVanWyk for my new word of the day!

Last edited by dyanoshak : 22-01-2013 at 18:42. Reason: props to EVW
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Unread 22-01-2013, 19:28
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Re: Interesting Jaguar Death

The Jag worked all of last year, and was pulled off and immediately put on this years chassis.Worked flawlessly Saturday, and died halfway through Sunday.

The mention of ESD makes me remember another student talking about static, was was complaining of it when he touched the chassis. Same student was reinstalling pwm cables after putting them in wire harnesses.

Might be onto something?

And I may have been mistaken but i think i recall a bit of water, might have just been a shadow or w/e (i doubt it was water, i'm ocd about liquid near the robot) around the brake coast,encoder, limit switch pins. Could that be a low enough resistance short to pop the diodes?

Can the diodes be tested in circuit?
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