FRC 3229 2019 Offseason WCD

Team 3229 is proud to present our offseason WCD. 2019 Chassis.step (21.9 MB) The design was heavily modeled after 5190 Green Hope Falcons.

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I think the versa cams are on the wrong side of the versablocks? At least, the way my team had it set-up, we had it so that turning the cams would push the versablocks away from the gearbox, which would tension the chain.

Yes, you are correct. The nautilus cams need to be on the opposite side of the blocks.

Thanks for letting me know! That makes a lot more sense than before.

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I would advise against running your chain in this way, it puts all the stress on the first chain loop. Look at how 254 ran their chains in 2017, that seems like a safer solution to me.

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Why. I know people stress about breaking teeth or chain but how often does that actually happen?

It’s just more wear overall, which means you’ll have to tension the chain more often and be at a higher risk of one of those more “catastrophic” failures that you’ve pointed out

Are you referring to using cams to tension the chains? I see that 254 used a fixed center-center, but wasn’t sure if that’s what you were talking about.

We broke a chain once (maybe twice) in the 2018 season. It was the chain from our back gearbox to our middle wheel, if we didn’t use the setup Korny mentioned we probably would have lost traction on our right side and not been able to make it back to the scale to win the match. Luckily our drivers didn’t even notice that it had come off and we just had to put it back on.

As for how often it happens, eh not much, but it isn’t really worth the risk. My guess is that some kind of carpet crud got into our chain run, and stuff like that is hard to predict.

If you were to put the battery onto the belly pan, would you need some extra support to keep it from sagging? I have read a lot of people using 1/8" polycarb for the belly pan and it seems like it would sag. I guess you could attach it to the front or back rail for support.
Thank you for publishing this. It looks like what we are planning to do.

The material in choice for the bellypan is 1/8” 6061 Aluminum, the bellypan is riveted to the chassis and we’d most likely mount the battery on its side close to the Versa. Hopefully when build season starts we’re able to pocket the bellypan and that’ll help with both weight and strength.

Why use aluminum over polycarbonate with a separate battery holder? it seems a bit unnecessary to use aluminum that thick for a bellypan, especially if you aren’t heavily pocketing.

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The design shown does not have any pocketing. We have limited capabilities as a team but do plan on pocketing during build season once we have a design planned out. The reason it’s as such is to leave it open to changes/custom designs on the robot.

No, I’m referring to running a chain from the gearbox to the center wheel, and another from the center wheel to the front wheel. Running it that way just puts all the stress on the first chain, instead of dividing it between them. What 254 did in 2017(it’s just the one documented example that I can think of) is they ran one chain from the gearbox to the center wheel, and another from the gearbox to the front wheel

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If you aren’t necessarily able to pocket, I would especially go with 1/16th 6061. 1/8th is heavy for a belly pan on its own, and since you’re riveting to the frame, .0625 will be enough.

Looks good! I do highly recommend using belts if you have the machining capabilities to hold a close enough tolerance. We’ve found that they are better for drivetrains since they don’t stretch as much as chain does. If you don’t use them though, a good chain tensioner is always another option. The only other thing I would recommend is changing up the placement of your gearboxes depending on the CG of your robot. If you do a low-to-the-ground robot like Dropkick, I’d actually recommend putting them in the middle since it will save you from unnecessary wheelies.

Definitely agree with the gearbox placement. In addition to what you said, if you break chain, you’d be direct driving your traction wheel that way.

But it also depends on spacing, sometimes you just need the space in the middle for something else.

The problems I see with belts is to use 15mm wide belts you add almost an inch to the length of your gearbox. Belts I would say are also harder to remove and replace at least from personal experience.

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Yeah, but if you can i’d put it in the middle. Also, instead of running chain from gearbox to A to B, you can go gearbox to A, gearbox to B for increased efficiency on axle B.