As was suggested in the thread about my plywood 8WD, I designed a sheet metal drivetrain. There’s nothing crazy unconventional in this one; sheet metal design was enough of a challenge.
-3-piece .080" 5052 aluminum chassis, inspired by 971/ 488/ 3847’s designs
-6x 4" 1.5" wide VEXpro traction wheels with blue nitrile tread. Center wheel is dropped 3/16"
-Outer wheels driven by 9mm belts on 30t pulleys. Belts are exact center-center distance.
-Custom 3-CIM gearbox with 6.82:1 reduction for an adjusted top speed of 11 ft/s. Gearbox plates are .25" aluminum; I might redesign them to use thinner metal.
-All components are accessible from the bottom.
-The part around the outside bearings is a spacer to keep the bearing from sticking outside the frame perimeter. In this render, it is 3d-printed plastic, but I realized that it would make more sense to use two stacked .080" aluminum plates, since it will bear significant load.
-Total weight of 36.4 lbs. The sheet metal chassis weighs 8.3 lbs.
Looks like my original comment was eaten, trying again.
Not bad. From my experience, I’d recommend making the following changes. Sorry if I come across a bit terse.
Move the flange from the sides of the belly pan to the rail, and make it the full length. That will make your frame stronger. I try my hardest to not break critical flanges like that to keep the strength up.
Make your frame as tall as you can get away with. Again, it will be stronger.
Put another bend on the inside of the front and back rails to make them stronger. I’d also make them at least 1.5", if not 2" deep. Our 2012 chassis has bent front and back rails from impacts, and is beefier than yours.
Lighten your rails more so you can see the belts/chain and get your hands in to fix it.
Not enough rivets on the corners. They will sheer in my experience.
How are you going to replace a belt when it breaks? Between matches?
The gearbox as you have it looks pretty difficult to manufacture. Extremely deep and narrow U-channels like that are hard to make with a press brake without some specially designed tooling.
Or is that two pieces? It’s a little hard to tell.
Either way, I’d suggest using a flat panel that bolts to the outside of the chassis rail instead. Laser cut bolt holes hold much better tolerances than bends, and you have to keep things pretty tight when center-center gear distances are concerned.
As per Joe G.'s advice, the gearbox is now two plates. The lightening pattern is improved and an access hole for the outer tensioners is added.
What tolerances can your shop hold on bends? I’m not sure your gearbox is going to mesh with your wheel correctly. You have the bend tolerance of the frame + the bend tolerance of the gearbox. For our shops, I would realistically say that that is ± 20 thou. For a gearbox, you want to hold ± 1 thou on c-c. 971 does this with a dowel pin and a tight tolerance slot in the gearbox plates. That makes it so the laser ends up holding all the tolerances, giving us essentially ± 1 thou on the c-c for the wheels.
I’ve found it really nice to have a square cutout above our wheels, and cutouts in the frame big enough for hands. That makes it really easy to see how your wheels are wearing, and to get your hands inside if you need to do something.