Re: pic: hmmm.
 

Haha, some nice replies here.

It's not that large or heavy, just a quick build from off the shelf materials.

There is a reason for the amount of standoffs...

Re: pic: hmmm.
 

Now that we are done competing with it. I can go into a little bit more detail about it. The hook weighs around 1lb. Not bad for an entire arm assembly with a weight of 6lbs to get an easy 2 points.

Now, does it still look "over engineered"?

We wrapped the winch cable in and out of all of the stand-offs, for one reason. Stability, I was scared that we would rip out a stand-off or the cable if we only put it around one of them. We never had a issues with it all and I was very happy.

Re: pic: hmmm.
 

I think it may actually be under designed. That's right, under designed.

Do you see a cable attachment point? How about a mounting mechanism? All I can say is, without the rest of the lifting system, this is very questionable.



Buuuuwaaaaahaha.

OK, now that the second image is available, it answers my question.


Ohhhh, I did it again!

Re: pic: hmmm.
 

I, for one, love this little enigma. Strong, light, easily built in a HS shop class. It gives me a warm fuzzy feeling when I imagine it holding 150lbs of blood, sweat and tears several feet above the hard floor.

Imitation is the sincerest of flattery... ...I stole the entire idea for 2849's hook once we ran out of weight for our pole climbing arm. You'll see something very like it in Baltimore over the next 3 days...

Joe J.

Re: pic: hmmm.
 

Actually, yes you are correct. We made some subtle but drastic changes and it's amazing how well it works now. We added two bolts onto the lexan pulley so the cable would not flop around and it hung very smooth and very fast. Too bad we fixed that friday night, not thursday.

Awesome! We did manage to hang for all of our last 3 matches. It was a beauty and made us all proud. Do you have any pictures of 2849?

Re: pic: hmmm.
 

I get that the tending stress is roughly (Mc/I = 12Mc/bh^3, c=.5, b=.25, h =1, M= 150lbs at 2in = 300in-lbs) = 7200psi add in normal stress of (F/A = F/bh) = 600 psi and you are still under 8,000psi. Well under Aluminum's yield stress.

I don't see buckling being a problem... ...plenty strong for me.

Joe J.

Re: pic: hmmm.
 

Absolutely no argument on strength. But, if you forget to include a way to attach it to your robot......... :yikes:


See my edit at the bottom of my post.

Re: pic: hmmm.
 

I'm still not seeing a problem.

We easily hang 150lbs off a similar hook (only with plastic spacers and the official screw of all right-thinking FIRSTers the 10-24). Our last one is the axle for a pulley with a loop of 1.9mm Spectra from Spearit.com all is well.

The only "tricks" are just to be sure that the axle gets loaded in double shear not in bending because over an inch span the stress can get a bit higher than I'd like and make sure to guide the cable to the middle so that one side doesn't take all the load over the other.

If those are the hardest issues I have to solve in FIRST, I'd be in good shape...

Joe J.

Re: pic: hmmm.
 

My first post was a poor attempt at a bit of humor to go along with the early part of the thread. It came just prior to Alex posting the picture of the hook on the robot.
It was sort of a two part pun.

The first part was pointing to the fact that the hook did not appear to have any obvious means of attaching it to a lifting mechanism, be it am arm or cable. The second part was a reference to the fact that it is shaped like a question mark.

Now, after Alex posted the second picture, the design intent became much clearer. Thus my edit with an additional reference back to earlier posts.

Re: pic: hmmm.
 

Our hook is a single piece of 3/4" aluminum, milled out in the shape of a hook. And you think *that* is overdesigned!

It was a beauty, and you guys should be proud. Well done, 3181, well done!