NeveRest60 chassis fault?

Technical Electrical
1

I’m posting this in electrical as a heads up for anyone experiencing this issue. In doing our in-house inspection before bag yesterday evening, the resistance between the negative battery terminal and the chassis was about 0.4 ohm, that is, a short. We looked around for pinched wires and such and didn’t find anything.
We disconnected the roboRIO power, as that would isolate about half of our systems from the PDP in one shot, and the fault went away. Pulling off one connector at a time showed that the fault was through the negative wire between one of our DIOs and the encoder of a NeveRest60. When we removed the encoder cowling to look for the cause, the short went away, and re-appeared when we replaced the cowling. Somewhere around halfway through installing the screws, the short appeared. As we were short on time, we left the screws out and taped the cowling in place, though we plan to replace the motor at competition.

Has anyone else seen this issue?

2

I’d like someone from AM to chime in here… this seems not so good. I’m also curious if the NR20s/40s have the same issue.

3

We had a short of an Arduino’s sensor wire to a bolt in our frame. We knew we had a problem because the compressor and motor outputs from the RoboRIO would stutter after sharp turns, but then recover after 5-10 seconds. Our terminal->frame resistance was on the order of 1.5 mega-ohms.

Did any of your outputs stutter?

4

We’ve found that the IR sensors we use have a conductive plastic housing–so it needs to be insulated from the frame for the same reason.

5

We haven’t coded for that motor yet, so I don’t know. In our case, it was not the wire, because we found the fault between the pin on the encoder and the chassis with the encoder cable (and I believe also the power wires) removed.

Oh yes, and I have PM’d a link to Billfred.

6

We had a 775 Pro do this to us a few years back, we figured it was the connectors we put on the electrical contacts bumping into the case of the motor and grounding to the frame. Thankfully the total resistance was within the acceptable limits and we got through inspection.

Never dealt with the NeveRest’s before but it looks like the original electrical contacts of the motor are probably similar to those found on 775s. Perhaps you can check to see if something in the encoder module is grounding to the motor case? It might not be the screws, per say, but something coming into contact with the motor case as a result of tightening the screws.

7

I have not heard of this happening before with a NR motor of any variety. They all use the same encoder on the back end. Please contact us at support [at] andymark.com and we will get you out a replacement motor! I will also send this along to our electrical and mechanical guys to see if they have heard of this before.

(In the interest of full disclosure, I am the manufacturing manager at AndyMark.)

8

Jon, thanks for commenting. This makes me feel better.

9

Will do. Unfortunately, we forgot to pull the motor before putting the robot in the bag, so it will be a month before we can send this one back. We have three others, and that’s the only place we’re using them, so we’re not in a rush from our end.