Chief Delphi - Interesting Jaguar Death

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Re: Interesting Jaguar Death

Im so happy you asked this question

Today the same thing happened to our team and actually the real weird part is it was the same black jaguar with that same tick-tick noise.

So what happened was that we turned our robot on and we hear that tick-tick noise, so we immediately turn the robot off. Upon farther inspection we thought it might the result of a faulty wire/ PWM cable. So we remove the PWM cable and the noise goes away. Therefore we got an other PWM cable, plugged her in, and the next thing we notice, the black jaguar does up in smoke, causing the other jaguar beside it to do the same thing.

So we really dont know whats the actually problem, but we were hinting its either the PWM cables (hardly likely) or the wiring of the robot.

Re: Interesting Jaguar Death

Quote:

Originally Posted by jp1247 (Post 1220226)

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?

Even with the ESD diodes there is always a chance you can damage something. Also, water is never good. You mention it being near the encoder input... the only external tap for the 5V rail is on the encoder input.

I don't think that a temporary short between 5V and something else would cause this issue. However, I have never tested that exact scenario.

I would do three things. First, with the Jaguar unpowered, use a multimeter (in either resistance mode or continuity mode) to look for a short between 5V and ground. Connect probes between the "+" and "-" pins of the encoder input.

Second, I would look at the 5V rail on an oscilloscope with the Jaguar powered and clicking. If you can, take a screen shot of the waveform and post it here.

Third, take a look at the inside of the bottom case plate. There is a hole that is covered by a sticker. That sticker acts as a great debris evidence collector. Any shiny specs, no matter how tiny, indicate that there is/was debris in the Jaguar. You can never predict when debris will cause damage. It may work an entire season and fail after you've moved it around and put it on another robot.

-David

Re: Interesting Jaguar Death

So, today i metered the 5v and 0v pins on the encoder out, and got 180 ohms, not good. A mentor also had their O-scope there, and here is the snapshot of the 5v pin. 1 Volt/division, 3.2 volts total.

http://imgur.com/pQKjvrR

The noise is also a very loud click, sounds like a decent sized relay, or possibly arcing?