pic: Team230 Damaged Frame Rail



Amazing the damage done by crossing a few defenses at week 1 Waterbury district event… LOL. Looks like the Hulk stuck his thumb in a pulled the bearing right out. :o Luckily we were able to replace the frame rails on both sides with material twice as thick during our 6 hours out of bag time before our week 3 event at Dartmouth. It held up great at that event and we are on to our 3rd event in Maine next week.

What thickness tubing is that? What kind of wheels did you use?

Looking at that I’d guess that adding a spacer in there would have helped by not allowing the walls to fold in and tear even with the same thickness aluminum material. Those thin walls were the only thing supporting the axles.

I was at Waterbury both days and some of those robots hit the defenses at high speed and caught air at times. You really don’t know at times how well some parts will hold up until you give them the real live test!

At least it wasn’t caused by us this time!

That’s 0.062" wall thickness 6061-T6 tubing. The drivetrain is 6WD, 8" pneumatic tires in a WCD (cantilevered) configuration.

It was the ramparts that did us in, with that big shot to one wheel at the start of each crossing. We told our driver to drive it as if he stole it, and he did not disappoint. :slight_smile:

A spacer within the tube may have bought us time, but failure was inevitable. the other side of the tubing has significant stress cracks. As it was, the thing made it halfway through its 17th match before it failed. The new frame ( 0.125" wall thickness) seems bulletproof so far. We would have started off with that if we’d fully understood the brutality of this game.

Not his time, but district champs are coming up. :slight_smile:

Yeah all of the teams I work with are using 0.125" frame rails and we haven’t seen any damage at all.

You said this drivetrain was in a WCD configuration, but you seem to have described a timebomb.

Source: built a timebomb in 2014. It was not fun.

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Now that the season is over, could I ask how well the 1/8" wall tubing held up? Would you need bearing blocks with the 1/8" tubing like with 1/16"?

I can’t speak for 230, but 4901 never replaced any of their 1/8" wall tubing through two competitions and demos. The final exam would be next weekend at SCRIW.

We’ve also been doing some playing with our 2016 robot at off-season outreach events quite a bit. I can say with some certainty that 0.125" wall tubing holds up without bearing blocks.

.125 tubing checking in, we’re good with no blocks and no spacers.

MOE also used 1/8" wall but with press fit rings bridging the gap between the inner and outer bearings, still runs great after 80 matches and a few miles of parade route.

The drive is not something you want to take…lightly… :smiley:

1619 ran an 8WD with 6" pneumatic wheels/tires in a West Coast config with bearings pressed directly into .1" VEX 1"x2" tubing with zero issues. Our machine competed at 2 regionals, Champs, IRI and a handful of “street demo” events (where our students decided to use curbs and parking barriers as makeshift Defenses).

Running spacers inside the tube wouldn’t have been an option for us because we run a chain-in-tube set-up.

Thank you all for the insights. Our team has been looking into trying a west coast drive this fall and this really helps. What other tips or tricks do you guys have in regards to west coast drive?

Whether 4901’s design really is or isn’t WCD is a fair question (we supported both ends of the shaft out of concern for the game), but we were running chain-in-tube as many WCDs do.

  1. When dead-spacing chain, the term “designing an even number of links” means “2, 4, 6, 8” not “integer”. Use a calculator; we like this one.
  2. If you must run half-links because you ignored 1 or had a very good reason, make it the kind that don’t have the little retaining pin you bend. That pin will be busted off by the other chain, and you will throw it, and you will be fishing new chain into your tube. (McMaster-Carr sells the good stuff.)
  3. Dark Soul tool is so much better for making complete chain loops than any master link. Even the normal master link will, invariably, be busted off and you will throw a chain.
  4. Design your drivetrain so you can get the main rail off without too much fuss. Riveting your belly pan every inch or so is too much fuss. (This was our greatest issue once we sorted out the chain; haven’t designed a better plan yet.)
  5. Drive your drivetrain early and often, to make sure your teething problems happen at home and not at your event. (You should be doing this anyway, but especially when you’re doing a new-to-you drive system.)

Do you have any preliminary thoughts on how to design a belly pan such that the main rails can be taken off easily? I think that’s a tough balance to find, considering that a belly pan has to be mounted properly to impart torsional strength to the chassis. Do you know of any teams that have worked this out?

2590 Nemesis would be a great team to chime in on this. I know in 2014and 2016their rails were designed to be removable.

Those are some gorgeous drivetrains. You can see a lot of thought when into many critical factors. The staggering of the rivets to not interfere with the runs of chain, the flexible coupling on the back axles for encoder mounting, and the way they’ve done the tabs in the belly pan are things I’ll have to remember.

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https://drive.google.com/open?id=0B43g8oXHbXVwTXp5YWtVdGUwNlprM21sR2FaQ3RxVWo2QTVJ

So I’m wondering if more teams do this? ^^ It’s hard to tell from the picture but we welded thick wall aluminum tube (can’t remember exact thickness) into the rail and then machined the weld flat and used a boring bar to achieve the diameter we wanted for the bearing. I feel like this would have prevented the damage to the rail in the original picture. What are your thoughts? Why don’t other teams do this? Is it unnecessary? Do I just have no idea what I’m talking about? I am very curious.