Hello chassis and drivetrain experts of FRC!
Our team (FRC 5459 Ipswich TIGERS) recently designed a custom chassis in CAD ahead of the upcoming game reveal. We are predicting some kind of pick-and-place, elevator robot game.
In the spirit of trying to prevent “tall robot syndrome” (robots with a COM high off the ground landing flat on their face after stopping short or getting bumped by another bot) caused by the traditional AndyMark kit chassis with center point drop 6WD, we have designed a chassis for a 6WD drivetrain with no drop in the center shaft.
Other features we have thought to include so far:
-(Almost) square orientation
-Mounting holes for popular 2-motor drivetrain gearboxes (EVO series, WCP SS)
-Made from 2x1x0.125" aluminum tube stock and 2x0.75x0.125" c-channel that we can easily get OTS
-Omni wheels (Vex) on the four corners to prevent drag when turning
-AM traction wheels in the center to give us, well, traction
-Multiple bolt holes to support 4", 6", or 8" wheels at proper distances for belt tensioning
-Lightening holes for weight reduction and aesthetics (of course)
-20 mm 80/20 used as stand-offs between the inner and outer side plates (more surface contact than churros, hopefully sturdier and more standoffish, albeit heavier)
We would love some constructive criticism on what we can improve upon with this design before we send it off to be machined by our CNC sponsor. If anyone has built (or driven!) a robot with a 6WD drivetrain and omnis on the corners, I’m dying to know about your experience!
CAD Link: Onshape
Looks reasonable. I recommend you consider a “West Coast Drive” arrangement though, as it makes replacing the wheels a lot easier (although it makes mounting the bumpers a little trickier). Andymark now sells a WCD chassis kit if you want inspiration: https://www.andymark.com/products/west-coast-drive-chassis
You might not need to do lightening, you can get away with just thinner tube to an extent. Another thing to avoid is 80/20 Tslotted aluminum, it’s excessively heavy, and you can make better use of that weight elsewhere. Other than that it looks pretty good. Depending on the game you might want to consider treaded traction wheels; while they are more expensive, they’re cheaper overall if you’re having to swap out your traction wheels 2-3 times per season(as my team did last year).
“no center drop”: the year I first ran that, I got betrayed by subtle difference in wheel diameters. Look really carefully at actual wheel dimensions.
In particular 5.875" colsons + 6" vex Omni is what got me that year.
So true!!! I almost was victimized by Vex’s version of a “6 inch” traction wheel which turned out to have a 6.25" diameter when I put it in CAD.
Looks like the AndyMark traction (and placation) wheels and the Omni wheels from Vex both have a true 6" diameter though, so that’s what I would go with.
I remember having trouble getting the 6" plaction to dig in when we did four level bearing holes? It was a mess. We actually ended up with four inflated wheels.
Looks pretty good to me! The only thing I would change is the orientation of the battery. Having it laying flat helps, even if just a bit, with lowering your COG.