First CAD of a WCD, how did I do?

https://cad.onshape.com/documents/697207e2fe24e7edbb988915/w/28df6a7204e9e92ee847164d/e/c5053d8479e3307c9d6f70a8

My team is hopefully going to do a custom drivetrain for the first time in recent memory this year, and I’ve been practicing CAD for it. Is there anything about this that could be improved, or that should be done differently?

Also, I haven’t yet put all of the fasteners into the bumper mounts (will be done soon)

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Don’t forget the belly pan as that’s important. The rails on the outside are for bumpers right?

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Looks real good. How far did you drop the center wheels? It looks like quite a lot.

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Yep, the rails are for the bumpers. And I’m planning to add a belly pan, still need to decide what it’s gonna be made of.

It’s the built in drop in the VersaBlocks, so I think 1/8" in total

They look good, might just want to make it a bit lighter

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Your drivetrain is currently geared for 24.77 ft/s. That’s very fast.

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I think all of the tubes are 1/8" right now, I will probably make some or most of it 1/16" tubing later on, especially the bumper mounts

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Also I would like to point out that the frame perimeter is exactly 117 inches (I am on team 117)

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Yeah I didn’t really pay attention to the gears at all I just used whatever was in the CAD of the gearboxes that WCP provided, I’ll probably fix that at some point - but thanks for pointing it out

You don’t need the front and back bumper rails - just use the frame rails to support the bumpers there.

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Does that violate R26 or not?

Take the “bottom left” corner for example:

Before the corner on the left, it’s supported by the bumper rail.
After the corner on the bottom, it’s supported by the bumper rail, then the angled 3x1, then the frame rail.

You don’t even need it to be supported by the angled 3x1, since the 1x1 bumper rail supports the bumper for more than 1/4" on the corner.

TLDR: Yes, it’s legal.

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Looks really good! Some suggestions:

  • You can move the front and back spacers for the bumper rails inside the the frame (rather than outside). That would give you a few more inches of belly pan space for electronics. Unless you’ve done it your way for a reason I can’t see.
  • you can get rid of the bumper rail spacers at the corners. The front and back spacers will do the job. That will let you push the front and back wheels 1-2" closer to the corner for more stability (although you may have shave the corner gussets to allow the versablocks to squeeze past.
  • we’ve sworn off # 25 chain in WCD chassis (with sprockets smaller than 3" diameter, and especially with wheels bigger than 4") in favour of # 35, but that’s a matter of preference.

I hope you get to build this one day. There’s nothing more satisfying then seeing a design move from brain to reality IMO.

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Makes sense, thank you!

That’s true. You could get rid of the front rail completely, depending on how your bumper attaches. The front bumper (or part of bumper) can attach directly to the front beam of the chassis.

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Thank you for the advice, I appreciate it!

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One thing I am concerned about is that the bumper rail itself is only strong in one direction if I do that, is that something I should be worried about or not?

If you’re worried about strength, think about what happens when you get hit:

When you get hit from the front, the impact will go through your bumpers and into your frame. The weakest link here is probably the bumpers themselves.

When you get hit from the side, the impact will go through your bumpers, through the bumper rail, though the bumper rail supports, and into your frame. In this case, the weakest link is probably the bumper rail supports.

Assuming you want to increase strength, you should focus on strengthening your bumper rail supports. In this case, what’s really weakening them is that angle cut. If you take away that cut, at least on the bottom, it’ll be a lot harder to bend it from an impact.

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You can save some space by moving the bumper mounting rails above the wheel, that way it doesn’t increase your frame perimeter needlessly (meaning more build space on the drive train itself)

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