pic: Simple Inverted BallShifter 2+2 Design

Working on adding more space to a simple sheet-metal chassis design that we will likely implement next year.

All sheet is .063 with multiple bends and inner braces/standoffs to add strength and rigidity. Torsional rigidity is a bit low but will stiffen with an extra center brace and more parts on top. Rails are covered to allow mounting of electronics/pneumatics.

Simple belt paths for 9mm belt and a 30:42 external reduction with the same reductions as last year for:
Free: Loaded:
HG: 21.50 ft/s 17.41 ft/s
LG: 8.12 ft/s 6.58 ft/s

It’s a a bit of a tight fit with the 30:42 reduction and is a bit nicer with a 24:42 reduction, but results in quite a bit slower bot (but still usable!).

Free:	Loaded:

HG: 18.76 ft/s 15.20 ft/s
LG: 7.09 ft/s 5.74 ft/s

This design allows the rails to be just 2.5" wide and still retain similar robot length and width to a rectangular design. Difference is less than an inch which is well within the dimensions that we undersize to pass inspection.

Inverting the ballshifters is the trickiest part of this design. I haven’t disassembled ours yet, but the 30:54 shifting stage actually has to be reversed (remove the clip and switch order) and new CIM holes drilled (or another case of the same type). We might end up 3D printing a custom casing from Nylon if we run into problems repurposing the Vex components.

Very interesting modification to the ballshifter; I wonder if buying an extra housing would make this easier. Might be hard to fit that configuration in a non-hex chassis, but with a 3rd stage WCD that might be a bit easier.
Great selection of speeds. The 19fps high gear is probably more than fast enough depending on your driver.
What size pulleys are you using? I’ve heard that 9mm wide 5mm HTD belts are pushing it with 24t pulleys on 4" wheels.

This might work better with the addition of the 3rd-Stage reduction module, that would push the gearboxes further into the chassis allowing the motors to not protrude as much, plus it would help with direct-drive and allow for a more traditional 6wd configuration (assuming you have enough clearance, smaller wheels perhaps?).

Why shift with a 2+2?

Not having a top flange on those extremely thin crossmembers is really going to compromise the rigidity of this set-up.

What’s wrong with that?
And +1 to Chris’s point, I didn’t see that.

I’m not saying it’s wrong, I’m asking what the reasoning behind it is.