Ball diffs can be scaled up. Getting them to work right in any application is about the preload adjustment; too loose, they slip, too tight, they are basically spools. Now I'm gonna have to do it as proof of concept for ya
Of course, I'm not talking about using one in a PW gearbox which drives only one wheel. Only way that would work is to have a shaft that mechnically couples the gearboxes. No, I build live axles for BPROs. This is the rear axle for the Wrangler build, upgraded this week with a 500W MY1020 can:
The gears, motor, bearings, wheels/Tires and brake parts were purchased and modified. The entire housing, the differential, the axle shafts, etc. were built from raw stock.
this will more resemble the clutch design that Traxxas uses except I imagine the clutch pad will need to be a large ring, not 3 little pads.
Traxxas is the oddball, using pads or friction pellets. Most makes use a single or double friction ring design. This is an Associated V2 slipper, which would probably be more easily incorporated into a BPRO gearbox:
If I were going to incorporate one into a BPRO, I'd put it as close to the motor as possible. Hard part is going to be tuning it right so that it does what it's supposed to without getting burned up by little people who don't let off the throttle when the vehicle stops moving! This is what caused repeated motor failure in my Wrangler build; the thing was powerful enough to carry >200 lb adults with ease, but the really grippy Kenda tires wouldn't spin when the kids ran into something or otherwise bound them up, locking the rotors and smoking brushes & commutator segments.
I think to make this a workable design, it's going to have to be adjustable by the end user, and adjustment no more difficult than removing a wheel. The preload is going to have to be adjusted for different vehicle and payload weights. If I had an extra 7R assembly here, I'd be able to offer more input, but going off of memory and images only, I'd say you'll want to use first gear, and it's gonna need a threaded hollow shaft that will fit over the stock stud in the GB, but allow you to have a spring with nut adjustment for tension. Going to have to make an inboard hub, and make the outboard hub part of the 1st gear pinion. To further complicate things, you'll need to have a bearing surface on the portion of the shaft that contacts the outer case half, meaning you'll need some kind of sleeve that exists on the outside of the tension spring with a flanged bearing to ride in the case.
This would be easy to accomplish with a totally custom gear box, but making it compatible with a stock housing is gonna be a little tricky. I think you'll end up having to sell it as a gearbox assembly rather than just a gear that the end user installs.
- By charlesrg
- By lj1sb
