Power Distibution Board - Broken stud

[Ether]

http://www.chiefdelphi.com/forums/sh...90#post1240690

Are these two problems related?

[de_]

Kevin, Where are you getting your data re other teams experiences re the stud ? Have you surveyed them ?

I have already stated I know exactly why how the current PDE ended up as is. So don't go there.

I can tell you 0 studs failed on the previous design (that was a $30 part). They were not brass.

[Kevin Sevcik]

Originally Posted by de_

Kevin, Where are you getting your data re other teams experiences re the stud ? Have you surveyed them ?

I have already stated I know exactly why how the current PDE ended up as is. So don't go there.

I can tell you 0 studs failed on the previous design (that was a $30 part). They were not brass.

Nothing scientific, just subjective impression based off the teams I work with here in Texas, and the lack of outcry on CD. If it was a very common problem, you'd see a lot more about it here. Look at the kerfuffle on the BAG Motors. By Paul Copioli's count, it's something that's affecting a very small percentage of motors, but there's several teams on here talking about it.

[FrankJ]

Here is a data point: We have six of these boards on various robots. We have one a broken stud. Relatively untrained student screwed on a 1/4-20 nut with an experienced mentor looking over her shoulder. Definitely operator error in our case.

We are now powering that PD board through a Wago connector for a test bed.

[FrankJ]

So where did it fail? Is it at the button of the stud where it transitions to the square? Does the nut turn freely on the stud? Was the stud bent or the threads damaged?

You are never going to get a grade 8 fastener in this application. You can teach the difference without going into metallurgy.

Occasionally even the best of us make mistakes. I would like to say it wasn't so.

[Richard Wallace]

The PD shanks are fragile, when compared against steel M6 screws. The PDB doc (here) states, on p.7, that the shanks can shear if torqued to more that 3.9 N-m. That's about four pounds of force at the far end of an eight inch wrench. Not nearly as much torque as is typically recommended for steel M6 screws -- about 10 N-m for Class 8.8 or 15 N-m for Class 10.9.

However, the OP clearly stated that the person with the wrench was a veteran electrical mentor guy. I agree this one is probably just bad luck. One of the best students on our team had similar bad luck a couple of years ago.