Tech Inspection

[Dale(294engr]]

Originally Posted by iambujo

We just failed inspection, with a chassis to PDB resistance of about 970 KOhm to ~1 Mega Ohm. I was not there so I was unable to help troubleshoot or get a better understanding of the situation. Last I checked though, 1 Mega Ohm is indeed greater than 10 K ohms.

I was told (second hand) that we were told it indicated a short somewhere. It's late and has been a long week at work, but I am currently failing to see the logic that it indicates a short.

Any thoughts? Anything I could be missing? I can certainly help try and isolate branches (remove breakers 1 at a time, visually inspect wires and sensors, etc) but 1M is > 10K so I just fail to see how it is a sign of a problem. I am sure someone will enlighten me here though.

970K indicates a potential problem that needs tracked down.

Can be EXTREMELY difficult to trace.. better done BEFORE competition starts.

I've spent half day helping a team disconnecting everything until culprit was isolated.. a good team too.. 207 from LA!!

When doing RESISTANCE test: swap probe leads to check BOTH polarities.

Shorts often exhibit diode behavior due to intervening multi semiconductor paths.

The Lowest R reading rules and must be >10K to pass.. BUT-->

Anything around 100K is a problem in spite of 10k spec. if you don't want sporatic random robot resets during competition!!

Good robots will read infinity!!
there should be nothing conductive at all to chassis. >2M (Harbor Freight) to >40M ohm (industrial grade)

Do you use a 1M potentiometer by chance??
a bit high to use for position or most sensor feedback applics, just a thought

RS-775 tab to case shorts are usually around 1 ohm AT motor

.. however when routed thru H-bridge of Jag's or Victors can show up as ~100k.. I believe Team 207's last yr was 200-300k & asymmetrical when ohmmeter leads were swapped.. they had 2 case to tab, 775 shorts!
And all new ones left in Spare Parts were shorted! (6)

GP: Attention teams possessing good 775's & NOT using them
PLEASE bring unused RS-775's to competition: Pitt announce they're available

To troubleshoot..
Remove both leads from one motor / device at a time until R changes
.. use lower of swapped values as it is more solid
(higher reverse resistances often waver around a bit making ya crazy)

Good luck...