torque spec?

[grambo]

Anyone have a torque spec for the large terminals on the new power distribution board? I snapped off about half of our negative terminal when we assembled our kit a couple weeks ago... It's been hanging on by a thread (maybe two) so far on our old robot. Definitely a mistake I'd rather not repeat once we get the kit of parts.

[AndyB]

I could just be uneducated here, but I don't think teams who received their controls early will be getting a second set in the KOP.

[billbo911]

Originally Posted by AndyB

I could just be uneducated here, but I don't think teams who received their controls early will be getting a second set in the KOP.

Nope, you are correct.

[EricVanWyk]

Wow. Whoever managed that just earned themself a nickname or two. Around the office we use the last name of a particular individual as a unit of torque. A "half-_____" is equal to the amount of torque necessary to irreversibly bind a bolt. A "full-____" is equal to the amount of torque necessary to destroy a bolt.

I am reasonably certain that you will not be able to return this PD, your best bet is to buy a new one from AndyMark.biz

The spec I have is "Torque 0.6N per Pin" (25 pins). Since I'd expect torque to be in Newton meters, I will check with the manufacturer for the actual spec.

[Russ Beavis]

YIKES!!!

Did you use a 1/4-20 nut or an M6 nut? Make sure that you're using an M6 nut. You've obviously got the positive terminal connected fine, though. Is it possible that you've got an M6 on the positive and a 1/4-20 on the negative?

http://www.we-online.com/website/fra...rDOCID=1010821

The PD uses the Wurth 7461098 shank for connections (see above for datasheet in "power elements"). Unfortunately, the above link doesn't include such specs but I'm guessing that someone knows how much torque is required to snap an M6 bolt of ? metal. I guess that it's possible that your shank was somehow defective in its metallurgy or machining.

At work, we call this much torque a "Hillis" or a "mega Hurley" (also 1 microHillis = 1 Hurley) in honor of a few of our staff. You might want to try using a shorter wrench next time (or maybe finger-tight in your case)

Oh snap...

Russ

[cdennisxlx2]

Originally Posted by grambo

Definitely a mistake I'd rather not repeat once we get the kit of parts.

AndyB is correct, you wont get a second one in your KOP [until 2010, lol]. The good thing is you can buy a new one Here

Hope that helps, good luck this season

[Teched3]

Just to add to the discussion:

Judging from you photo, the bolts look like they are brass, which would have a much lower yield strength than steel. Contact the manufacturer, as you may be able to replace the broken terminal bolt/nut. However, I am only guessing, since I haven't seen or handled the component as yet.

[Russ Beavis]

Unfortunately, the bolt is press-fit (one chance only) into the PD's PCB using, to my understanding, a massive press at Diversified Systems. In other words, it cannot be replaced since, even if you could push it back out of the PCB, it would probably never re-engage properly (too much damage to the PCB's through-holes).

Russ

[EricVanWyk]

Originally Posted by Russ Beavis

Unfortunately, the bolt is press-fit (one chance only) into the PD's PCB using, to my understanding, a massive press at Diversified Systems. In other words, it cannot be replaced since, even if you could push it back out of the PCB, it would probably never re-engage properly (too much damage to the PCB's through-holes).

Russ

The connector is rated for 250A continuous. To get that sort of ampacity, they literally shove square pegs into round holes - solder just wouldn't do it.

Very good for reducing the total resistance drop through the PD, not very good for fixing broken shanks.

[billbo911]

This is just a thought, and not a verified solution.

By the looks of this from the picture, there might still be about three threads left on the stud.
If you can find (or make) a M6 standoff with a male shaft on one end and a female on the other, you might just be able to "patch" this PD.
Make certain the female end engages the remaining stud by three threads, tighten it to spec. Then you should be able to connect the negative wire to the stud on the standoff.
Again, I would not use this repair on a competition robot, but it should be good enough to salvage this one for learning and practice robots.

Man, that was a $189.00 booboo.

[Al Skierkiewicz]

Erik and Russ,
We also have a whole specification of measurements based on the OR (for Ed Or****) Since Ed was a rather large guy and was fond of using tools in much different configurations than their intended design, this table was developed.
1 OR=720 ft. lbs based on Ed's estimated weight and his penchant for using a 2' pipe to get better performance from his wrench.
Screwdrivers had to be able to survive as cold chisels and cresent wrenches needed to double duty as hammers. To give you and idea of his power, a co-worker once glued his toolbox in place on a formica covered bench using RTV. (It was a joke, you had to be there) When he attempted to remove it, he lifted a rather large oval shaped piece of the formica covering from the bench top. The formica and tool box lived as a single unit for many years. Ed is now retired and so is the toolbox. On occassion he was known to measure distance in femto parsecs.

[EricVanWyk]

I just finished conversing with our Wurth rep. He send me a small ppt with the appropriate specs. I can email it to you if you'd like. Unfortunately, it is pictures of text with bad compression...

Summary:

Max Torque 3.9 Nm -
Break torque 10 Nm - Destruction of threaded shank
Break Torque 25 Nm - Destruction of the press-fit pins


Upon seeing the photos, his immediate response was that you probably used a 1/4-20 nut instead of an M6 and then cranked it. I'm not sure what the root cause is, but we can swing this as a reminder to all teams:

Only use M6 nuts on the PD Shanks.
Don't force any connectors.


More Info just received (in new legible text format!!):

Mechanical properties (reference values):
Material: CuZn39Pb3
Shear-off force: 350 N/mm²
Tensile force: 480 N/mm²
Tensile yield strength : 340 N/mm²
Elongation: 20%
E-Module: 96 kN/mm²
Torsion-Module: 32 kN/mm² (shear modulus)

[Mark McLeod]

When they heard about your plight a friend of mine suggested a very temporary workaround would be to employ one or more of the unused 40A return lines to replace your "-" terminal.

That'd only work if you could insure that your load didn't get too high. That Wago is only rated for 76A continuous, but it will be much better than using a unknown fix for the shank.

Best to just buy a new one...

[MrForbes]

I noticed a new robot student tightening the nut on one of the terminals with a ratchet, and said "that's tight enough!" just in time

This was after another mentor had to go to his truck to find a 10mm socket.

Thanks for posting this warning, this is good info on this thread

[grambo]

...yah i think i will be getting a new nickname this year...

the damage was done with a common 1/4" drive ratchet with about 6" or 8" arm, a seemingly harmless tool for the job. ...and yes, we were using the M6 nut that came with the board, and it's the same one that's on there now. I've used PEM studs before on a number of projects and I've never seen them torque out or snap like this one did. I'll definitely be contacting AndyMark and see what we can work out on this. We'll probably front the money for a new one and see if we can wait until after the competition to return the broken one and see if it was a metallurgical flaw (I hope that's what it was). The broken portion has an odd texture to it that I'm unfamiliar with, although I must admit my training is EE and CS, not so much mechanical.