Well, honestly we’re not exactly sure HOW it happened.
I’m waiting on match footage to help me determine it exactly.
What is evident, is that we were hit several times below the bumpers and on our frame perimeter, probably by an opposing robot’s intake/appendage.
(Though we do know for sure that a sizable dent was created by an alliance partner in quals, considering some of their powder coat had been left on it.)
As for prevention, I’m not entirely sure to what degree anyone can prevent this from happening (aside from extra/different bracing and structure.) The refs are looking for in-frame contact out on the field, but anything below the bumpers is hard to see, for both them and the drivers. Robots have extensions, and collisions WILL happen.
Stuff like this happens out there on the field. The most we can do is be ready to fix it if it goes.
This is a great example of a member where tubing or C-channel would do a far, far better job than flat plate and standoffs. All of your strength is on the wrong axis, and you have very little resistance to bending.
Looking at the damage, and the structure of that frame I’m not really surprised that it failed the way it did. There seems to be little “thickness” in that area (other than a few churros). L-bracket (or a ‘rib’ down the length of the front) might have served as better protection.
Which is why our chassis is made of the old C-channel kitbot (2005-era that you can get from VexPro). And why we bolted a piece of C-channel to our flat plate on the intake. And most everything else is 80/20. And it weighs <90 lbs.
Funny since it’s been described as “heavy as elephants”.
Just wondering, was there a reason your team chose to use plates and standoffs, as opposed to a more traditional approach using tubing? It seems like using plates and standoffs is more difficult to manufacture, potentially heavier, and significantly weaker. Just my .02$. Chow out.
As weird as it sounds, our machining resources for plate are far easier and more accessible than anything we could do for tubing. For us, this was far easier to manufacture and turned out lighter than tube would have been.
As for the last point, you’re right. It is significantly weaker on the axis the drive train would take hits on. That’s why when the front portion broke, the replacement was 2x1 tubing.
We’re still extremely happy with the drive train, a game with defense as high as this one’s was just definitely not the year to run it.
Plate, at least with 125’s resources, is far easier to work with. We can do tube but it’s 4 ops to lighten that as opposed to the 3/16" plate we used in our DT where we machine plates for both sides of the bot at the same time. (video) Our drive frame hasn’t had any problems through nearly 20 matches at Groton (lots of replays) Nor has our intake which was built using a similar technique.
We tried to waterjet 4x2x0.125 tubing using PINK’s method to only cut 1 side of the tube at a time, but the sponsor said they couldn’t make it work on sample pieces. Luckily they had an in-house CNC and all it caused was 1.5 weeks of delay to get it done right.
We use an aluminum cutting circular saw blade on a miter saw to slice our tubing (I think it is a $120ish blade). We used 1x1x1/16" and 1x2x1/8" tubing to build our frame.
We also use some cool corner stiffener inserts to keep the whole thing square. Our tolerances come to 1/32" with our most experienced student at work. The welding gives us the most tolerance troubles, but we are less than 1/16" everywhere
We use a horizontal bandsaw with automatic shutoff and plenty of cutting fluid to cut the pieces to near-perfect length. Then we tape all same-length frame members together so that they’re flush on one end, and go to a wide belt sander. We sand one side of the taped tubes so it’s square and the other side is sanded down so that all tubes are identical lengths. This year I think we were under 1/32" off, or basically less than a single tick of the tape measure. We then adjust CAD if necessary. We’ve become better at tolerances, so usually no CAD adjustment is necessary. While the welds have never been perfect (the rails always warp just a tiny bit) they’re much better than we used to do.
I should have put that the waterjet/CNC was to cut mount holes & pockets into the 4x2 since it’s so heavy.