pic: Team 399's arm after the SD finals match 1.


Any thoughts on what caused the failure?

I watched the claw appear to twist while you guys were near the Blue Alliance pegs attempting to hang. I thought it looked odd, guess it was really the arm that was twisting. Then it was, OMG their arm came off!

Sorry that had to happen.

As soon as I saw your alliance with 1504, I leaned over to my neighbor and said “It will be them and #1 alliance in the finals”. I knew your alliance was going to be strong, too bad it had to end like it did.

Good luck in the rest of your competitions!

Looks stressful.

Is it really surprising that the arm failed given the quite drastic lightening pattern used on the arm?

Definitely a bummer but maybe side on the side of slightly overbuilt versus one hit away from total failure. Also maybe look into fiberglass to save weight without having to be cheeseholed

Wow, that’s a bummer. It’s also a tough way to learn about why tubes should be left tubular, and not cut away…

when i first saw this i thought it was wood. bummer but for replacement thinner walls usually make for a tougher/weight ratio than thick walls pocketed.

Is that break also further up the arm? (closer to the pivot)

If you want to pocket, use a smaller diameter and also just use regular holes instead of large slots like this one.

From what I saw in the video of Final 1, it looks like the arm broke close to the pivot point, probably within 3" or so. (But I could be wrong.)

That’s what it looked like from the stands, the break was just beyond the pivot point.

Thanks for a great alliance guys. Nice being with 399 and 1540 as well as 294 :smiley: Good luck at your next regional

The break was about 4" down from the pivot point. The initial end effector (pincher claw) was much lighter before weighing approximately 2lbs. Put a 6lbs roller claw out there (including the pocketing) and you can easily tell why this arm broke off. The stress by the end of the competition was too much.

I can assure you that our new arm will have much less holes by the time we go to LA. It’s a painful lesson to learn, particularly in the finals, but one that we will remember.

That is terrible, I only saw it from the stands, and it looked pretty bad even from up there. Hopefully you guys can get that fixed because that was one great robot.

I do have to thank you very much for allowing us to be substituted into your alliance

It was painful to watch, the arm broken inches away from the pivot, the rollers of the claw causing it to drive around away from the frame, and then to see your robot start smoking when attempting to deploy, all in the finals.

What are the specs on the material you used for your arm?

hope to see you guys up and running around stronger than before! see you in LA!

I doubt the arm failed because of its material properties but rather the lightening pattern. Strength of cross section is much more important than material choice.

An 1/8" version of this arm would be substantially stronger if it were 1/16" and left unlightened.

An unlighted 1/16" version would probably be stronger, but the question is, can you get the correct tubing size in 1/16" wall? I’ve been looking for tubing for our arm redesign, and usually only 1x1 and .75 x .75 tube come in a 1/16" wall.

Use thick wall square tubing at the ends, thin wall round tubing in the middle?

I don’t really have many ideas for using aluminum, both of the arms we’ve made were built with round plastic tube.

and strainful…


You can actually get 1.5" and 2" in 1/16".

Put some fiber in your robots diet and go composite. Like pultrusions. However be aware that construction methods for composites differ from metal.