Split Topic: Gusseting Bumper Supports for WCD-Style Drivetrains

One idea, I’m not sure if others have had this problem or not… We’ve done a WCD VersaChassis-ish design the past two years, with short pieces of 1x2 acting as standoffs, sticking out between the wheels as bumper supports, mounted with T-gussets. It more or less works, but every year the standoffs loosen up and get wobbly, while the gussets remain solid in main chassis. I’d love to see a COTS solution that would hold those in place better.

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We had a similar issue this year. Built our chassis wide, not catching until after it was cut that it was too short nose-to-tail for our arm. So we made a custom gusset that mounted two pieces of 2x1 tubing to it so the frame perimeter would be right. It definitely showed its age by the end of Smoky Mountains.

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We’ve had success using a short length of 2"x2" box tubing, bolted to the 2x1(or in our case, 2x1.5") and then mounting the bumpers to that. I think it’s a fairly robust and elegant solution, though it is definitely a bit on the heavy side.

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The nice thing is you have the option to drill these holes out if needed. You can always remove material, much harder to add it :slight_smile:

I remember @Ben_Martin mentioning using a piece of 80/20 or Walnut extrusion to do this by drilling / tapping holes into the extrusion. Might be another solution to try :thinking:

I hadn’t seen that, thanks for sharing! It seems like it could work better… but it would be nice to be able to use the same material we already keep in stock, if there was a solution for it.

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Can you tell what is deforming? Are the rivets getting smaller or the holes in the tubing and/or gussets getting larger? Is the freedom of motion greater in one direction than another?
What materials are you using (composition, thickness, diameter)?

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Vex 2x1 tubing and Vex T gussets. The first year we pop riveted them, using steel pop rivets of the appropriate size, both top and bottom. The second year we drilled the holes out for 10-32 x 2.5" bolts (using proper sized drill bits - we buy them in bulk for certain sizes!) and ran them through to some nylock nuts - we would have used 8-32’s without drilling out the holes, but didn’t have any long enough, while the 10-32’s are something we stock in a LOT of different sizes. The bolts held up a little better than the pop rivets, but are still looser than I would like. The freedom of movement is almost entirely side-to-side.

The standoffs are also drilled through on the ends to accommodate our bumper pins (1/4" diameter t-handle quick release pins 2.25" long), so rubbing force from the side bumpers do translate into those standoffs to some degree. The holes in the standoffs are likely becoming oblong, as the standoff is pushed in either direction against the two bolts (formerly pop rivets), but I haven’t pulled one apart to look at it.

A quality epoxy will go a long way to keeping those gussets where they belong.

I recommend taking this topic elsewhere if you guys will stay on it. It’s transitioned from product idea/issue to solutioning which i think is a bit of a topic for a new thread.

You could likely improve this considerably by using bolts in all four holes of the T-gusset which don’t interfere with your side rail. Assuming those machine screws have some shank (aren’t fully threaded), I’d suspect that most of the wear is at the end where the threads of the screw to through the gusset and tube wall, rather than the shank end. Especially if this is the case, I’d put the first and third in head up and the second and fourth head down.

Or alternately, eight steel rivets rather than four.

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You can cut a 2x1 and mount it vertically to make your bumper frame support piece. Here’s a 5 minute CAD example:

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Would this be a good place to use Walnut extrusion? Joined by a six hole pattern through one or both walls of the WCD rail.

Yep this works nicely. This robot has the 8020 oriented the other team way so we could face mount bumper brackets on top, but both ways make for easy to mount (but somewhat heavy) bumper standoff material.