We were building our robot today and were planning to test the moving arm. When we were building, we forgot to add washers and this is the result:
We were using REV MAXTubes and two 1:100 gearboxes with NEO 550s. It was supposed to have washers in the design, but when we were building, we forgot to add them.
You may want to look at a few other things as well to prevent this from happening, washers certainly will help -
You may also want to consider just using a thicker tube there as well if you have the weight -
We currently can’t get the pieces since we’re from Turkey, but we will keep these in mind for next season! Any other suggestions that we can do with local supplies?
We didn’t have any tube supports and didn’t 3D print spacers, so we just cut up some churros and placed them as supports in the tubing.
There actually were churros in the tubing, but not in that certain part 
The 3D printed spacer options posted above certainly will help fill the tube up to prevent crushing and using a larger washer should help as well.
It looks like from the video that you could fill the gap between this angled structure piece and the cross bar that pulled out. Maybe a 3D printed triangle block to fill the gap and help transfer some of the load into that part of the robot (or even a wood block cut to fit would work)
We will try this out tomorrow and come back with the results.
Also, limit switches and/or S/W limits on the arm angle.
And maybe ramp-up and ramp-down code to make the arm start and stop gently.
This didn’t help your situation either. REV uses thin 0.040" material on the 1" ends of all their tubes. This isn’t the reason it just didn’t help things. Using 0.125" wall would’ve helped but not solved the problem
Washers don’t load spread very far. The failure here is from design issues. @Ryan_Dognaux covered the solutions nicely.
When doing big chain driven joints (or any big joints) it is imperative to have a direct compression/tension member between the axles, e.g. a plate with two bearings to lock the axles at the right distance apart.
Good luck!
We cnc cut some of these last season to reinforce tubing (and for field repair when that happened). You can add it inside our out.
You can even repair the existing tubing in a pinch.
A crush blocks is probably going to also be helpful, and there are some 3D printed designs for this already.
This needs crush blocks, you can make them on a 3D printer, mill, CNC, hand drill and file or grinder. Whatever you have you can find a way to make crush blocks. I made some out of old bumper wood a few days ago.
Life saver for sure.
However, be careful when cutting them out. If you use screws to attach to the spoilboard when cutting the profile, you will end up giving them a trim. Broke a bit last year.
The official MaxTube inserts were out of stock, and the students needed some that have the holes at a funny angle, so I machined some out of aluminum on the mill. Took a long time, mostly because the only piece of solid billet stock we found that was big enough was rough-sawn.
Updates!
We added under parts out of aluminum and added big steel washers, and it all was working perfectly.
Then, we decided climbing and disaster struck again…
By “Disaster Struck Again” do you mean the tube crushing still shown in this picture?
I would read the recommendation on crush blocks above again. The ones sold by REV, or build your own by cutting a profile out of wood - the closer you make the crush block to the inner profile the better it will do at preventing this crushing action.
You can eliminate these structural failures by adding a load member between the two axles.
Currently it looks like the drive and shoulder sprocket are connected like this… leading to significant bending forces being resolved through the structure, including the tube segment that has failed again. The tension from the chain pulls the drive and shoulder together, bending the structure that holds them together.
Smiley face is bad.
If you add a member between the drive and shoulder, ideally one on each side, that will resolve the tension of the chain directly. The mounting of the drive and shoulder will have much less stress to deal with and you’ll likely be in good shape.
This doesn’t need to be fancy. A chunk of plastic plate with two holes would probably do the trick.
Two plates with some notches cut in them can be sandwiched around the axles, so no/limited disassembly required.
I know this works because I’ve had to do it before in a similar loading case on our 2018 (?) robot.
