Re: [HELP] Digital Sidecar troubles
 

We have really nice meters; advantages of our head coach being a s
Digital electronics teacher :D I'll have to do the checks at our meeting tonight

Re: [HELP] Digital Sidecar troubles
 

Interesting. I had never considered that AC voltmeters wouldn't measure voltage the way my fluke does. Nice post, thanks.

Re: [HELP] Digital Sidecar troubles
 

Flukes are primo. I am green with envy. :)

Re: [HELP] Digital Sidecar troubles
 

So I took apart two of the sidecars that stopped working. The insides were not pretty. Anyone have any idea what could be causing them to burn out so fast? We've checked over everything short of splitting the wires and inspecting individual strands, but came up short. Apart from the fact that our robot is frying sidecars like eggs, she's in perfect health.

Re: [HELP] Digital Sidecar troubles
 

That FET protects the rest of the sidecar if someone wires the power backwards. My bet is that you have a double chassis fault, and one of your motors is trying to use the sidecar as part of its return path.

Re: [HELP] Digital Sidecar troubles
 

Double chassis fault? The think I can't understand about this happening is we checked over our wiring twice, and it was all in order. Plus, the first sidecar that was on there was literally the first sidecar on the robot. It survived 3 competitions and an off season and then just decided to burn out and left an apparent curse on the rest of the sidecars plugged in. Can't really plug a Wago in backwards so that's out.

Re: [HELP] Digital Sidecar troubles
 

It's likely a short somewhere past the sidecar. Remember, shorts don't *just* happen when you first build a robot... any repairs or changes made to the robot could result in someone accidentally drilling through a wire without realizing it! It could be anything plugged into the sidecar... You have to diagnose everything plugged into it to see what isn't working properly.

Also, while a wago connector can't be plugged in backwards, it can be wired backwards... tripple check it. Then check it again :p

Re: [HELP] Digital Sidecar troubles
 

The part that fried is used to connect the ground signals within the DSC.
Attachment 13255
We had this happen to us and was caused by either +5V or +12V connecting to one of the ground pins [PWM or digital] on the DSC. We were troubleshooting and had 12V wire touch the PWM ground connection. Our board only had the top of the IC blow off, which looked like the blue PCB you showed.

Did you notice any smoke or electrical burnt smell when things stopped working.

-pete

Re: [HELP] Digital Sidecar troubles
 

Cal,
Eric has pointed out that Q1 is the reverse polarity protection device. So if you are sure that someone hasn't rewired the WAGO connector, I would start looking for a PWM cable that is laying across or next to a power lead. In this kind of fault, the FET is not going to be the only thing damaged. If you feel along PWM cables, one will likely have a textured feel indicating it has gotten hot during the fault. Often these occur where multiple wires run together across a rotating joint or inside a moving arm. As Jon pointed out, don't rule out the drilled fault either. I have seen stranger things, so it is possible that the fault has existed for a long time and is just now raising it's ugly head. The best way to trouble shoot at this time is an ohm meter measuring continuity between parts on the robot. I would start by checking each of the PWM cables first to chassis and then to battery terminals on the PD with the power off and all PWM cables disconnected from the DSC. All should read very high resistance, greater than 100K. If your probes are sharp enough, you can touch the contacts in the PWM block through the holes in the side. Alternately, a resistor lead wrapped around the probe and inserted into the end of the PWM connector also works.

Re: [HELP] Digital Sidecar troubles
 

Well, guess I know what I'm doing later today. I've got a date with an ohm meter and our robot. Should be fun.

Re: [HELP] Digital Sidecar troubles
 

Checked everything over and everything is isolated. Battery lugs to frame is open, each strand of the pwms to the chassis are open. Wago is wired correctly, also not shorting internally. Visually inspected the PWMs and they're not broken nor "bubbled."

Re: [HELP] Digital Sidecar troubles
 

Then it's probably an intermittent short that only occurs when a mechanism is in or passes through a particular position. Those are fun to trace down.

Re: [HELP] Digital Sidecar troubles
 

Um...how might we go about tracing that to see if that's the potential fault? And would this be an intermittent short across the PWMs or the motor controllers themselves?

Re: [HELP] Digital Sidecar troubles
 

You've got two faults: 1) a ground PWM connected to the DSL, 2) a 12v power feed that's somehow intermittently finding a path to the PWM ground line (this can be direct cable-to-cable or through some intermediary such as the robot frame or even yet another cable).

You've already narrowed down the list of possible culprits to one of the ground lines on the PWMs or DIOs plugged into the DSL. It's going to be a short that shows up only intermittently on one of the limited number of ground lines connected back to the DSL via one of the PWM cable ground lines.

The origin of the 12v can be anything on the robot connected to a live 12v power feed, so everything carrying 12v from the PDB to the motors are suspects. Some motor types can ground through their bolts to the frame, and may only conduct power when a certain winding with a worn spot is energized which means rotating the motor slowly through it's rotary motion. And remember the cRIO and camera chassis are both hot and need to be electrically isolated.

If your memory is good and you were systematic in your testing, then try to narrow your investigation down to the parts of the robot you were exercising just before you noticed the second DSL power LEDs went south.

You don't want to burn out another DSL, so testing for the shorting ground wire involves putting your multi-meter on each PWM cable ground line & the 12v power lug on the PDB one-at-a-time and moving the robot mechanisms by hand if possible.
It also involves shaking and moving the wires to stress them a little. Don't be gentle with your wire runs, put them under the same movements, vibrating, rubbing together that they undergo normally while the robot is racing around the field, bouncing off other robots and walls.

Searching for the shorting 12v line involves the same sort of continuity test for each of the 12v power pathways. A little tricky since you won't be able to power the motors, and continuity of the power pathway will be broken at the motor controllers.

Re: [HELP] Digital Sidecar troubles
 

Could it be an RS-775 case short?