torque spec?
 

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.

Re: torque spec?
 

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.

Re: torque spec?
 

Nope, you are correct.

Re: torque spec?
 

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.

Re: torque spec?
 

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

Re: torque spec?
 

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 :)

Re: torque spec?
 

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.

Re: torque spec?
 

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

Re: torque spec?
 

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.

Re: torque spec?
 

I have not seen the part either but here is a "handyman/shadetree/garage mechanic" fix for broken studs like this. Use a long nut to hold both pieces together. Drill down the center with an #30 or #29 drill in a drill press. It is important to go straight down. Drill through both pieces. You can remove the nut after you've drilled the hole. Now get a 1/8" brass rod and cut it the length of both pieces. File a flat on one side of the brass rod the entire length. File or cut a slot at one end about .030" wide and .0625" deep. Use a good flux and cover the surface of the brass rod and the hole you just drilled in both pieces. A Q-tip works well for getting the flux in the hole. Now you are going to solder the brass rod in the hole to join both pieces. The flat you filed in the rod will give the solder a path to flow down and the slot will allow you to use a small screwdriver to turn the brass rod to help all surfaces get covered with solder for good joint while it's hot and the solder is molten. Use a high wattage solder iron/gun or a torch works well also to produce enough heat over the large area.

Watch the heat carefully so you don't melt something you down want to melt.

Be very careful tightening the nut as it will only handle less than half the torque it did before you broke it. Good luck.

Re: torque spec?
 

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.

Re: torque spec?
 

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.

Re: torque spec?
 

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)

Re: torque spec?
 

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...

Re: torque spec?
 

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

Re: torque spec?
 

...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.

Re: torque spec?
 

Attaching the nut by only 1-2 threads has probably increased any effective 'resistance' the terminal has as well. If you overloaded the terminal with 120A, you would probably severely damage something, or really burn someone's hand if they touched it at the wrong moment. The point is -- it can't stay like that.

I'm also surprised the bolt snapped before the PCB cracked. I wonder if there are stress fractures where the stud connects to the PCB...which would again significantly increase the resistance of this terminal.

Sure, you can 'patch' it with a standoff as mentioned above, but for safety and reliability reasons, I would get a new one.

Re: torque spec?
 

Wow...a $200 mistake! Time for all teams to have a "be extra careful with the electronics" discussion.

http://andymark.biz/am-0265.html

I wonder if it would be possible to get repair parts for the power distribution board? The red/black plug in wire connectors are probably all soldered on...and there are some surface mount parts on the circuit board too....this might get interesting. If you can get the housing apart, the studs might be bolted on?

Re: torque spec?
 

Don't count on getting a new one next year. http://frcdirector.blogspot.com/2008...ol-system.html

Eric and Russ already described how they were attached. Unfortunately, it's not that easy.

Re: torque spec?
 

I just talked with Ben at Diversified Systems. He was initially thinking that this can be repaired, but recently he concluded that it cannot. So... the only thing to do is to replace this unit.

Thank you for posting this issue so that teams know that this is something to watch for.

Eric, Al, Mark, Russ, and all have given great advice in this thread, and the only extra suggestion I can give is to go out and get a 10mm nut driver to tighten this nut.

Sincerely,
Andy Baker

Re: torque spec?
 

This may work as a stop gap fix to make the thing work, but everyone should be aware that based on the rules from pretty much every year this would be highly illegal on an actual competition robot.

Re: torque spec?
 

Wow!! I can see this being a serious problem if caution is not taken. I had a team member tighten it without really considering the "Break Point". I was real close and was sure they didn't use excessive force. But WOW!

BTW...Awesome pics!!