Auto-shifting 2 Speed AND motor brake/reverse?

[BrianG]

I was thinking (uh-oh). I don't know of any auto-shifting two speed transmissions that also use the motor for brake and reverse. The OWB on first gear generally makes this impossible, which leaves you with mechanical brakes and no reverse - although some trannys like the Revo do allow for mechanical reverse, but they are brittle.

But, why not use another gear on a OWB, except flip the OWB around so it only engages when the motor spins the other way (which would also give motor braking). I did a quick diagram using the Revo tranny as a base design to illustrate:



While the motor is spinning forwards, first gear will provide the drive. Once a certain rpm hits, the centrifugal clutch on second gear kicks in. Since the shaft is spinning faster than first gear, the OWB allows first to free-wheel. Nothing new here. But, during all this, the reverse gear set in the diagram above is free-spinning due to its flipped OWB, and is essentially doing nothing.

When you brake or engage reverse, the centrifugal clutch lets go and the OWB on first gear free-wheels. So both first and second gears are doing nothing. But the OWB on the reverse gear set is now engaged allowing the motor to brake and/or reverse.

How does this sound?

[lincpimp]

Sounds correct, I had thought of the same thing and had the ability to describe it like your pic does. So who is going to try this idea out? I have enough parts to see if it will work. Will the OWB on the reverse gear be strong enough to handle braking duties?

[BrianG]

Well, since you have the parts, I nominate you to try it!

I don't see why it wouldn't be strong enough - the OWB on first gear accelerates the truck well enough...

[lincpimp]

Ok, I will try to scare all of the parts up tomorrow and see what I can do. Not sure if the revo tranny case will have enough room inside, but that is what I will start with...

Also, do you think the 2nd gear clutch will disengage fast enough? I know there is a fair amount of rotation (180deg) that the second gear can rotate and the clutch pawl not touch the steel pegs. Just did not want it locking the clutch pawl out under hard braking...

[What's_nitro?]

Brian, this type of thinking can be very dangerous...to the nitro owners!

It looks bullet-proof to me. I hope you can find a case to put it all in.

[George16]

I don't know if you consider that bullet proof but the pin that holds the OWB in place is only 2mm in diameter. I had broken that before on my nitro so I ended up drilling the shaft to 2.5mm so I can use a 2.5mm hardened rod.

[TruckBasher]

Well, hopefully Brian or linc can put them all together on the tranny case first for proof of concept...this is very interesting

[J3110]

How's it goin?
I've got an older T-Maxx .16 tranny that would be willing to act as a donor for this project as I fully intend to convert the old Maxx to BL eventually and this would be handy for obvious reasons.
While shifting into reverse would be alright, not having to would be ideal. Still, I'd lug around the shift linkage and servo for the 2-speed auto. :D

Looks like a great idea to me. I have 2 revo tranny's downstairs. My forward gears are buggered up though. I'll dig around and see if I have enough good gears to attempt something like this.

[trev3813]

umm, kinda obvious question here, whats OWB?

[TruckBasher]

one way bearing...if Im not wrong...

[TexasSP]

The one way should hold up well enough. I used them in some machines we built last year for a wire feeding device and they worked well as long as no radial load was applied that put pressure on the inner bearings. Since this won't be the case in the tranny all should go well.

The hardest part of my endeavor was finding the bearings. Believe it or not one-way bearings or locking needle bearings are not easy to find. Here is the best source I was able to find and that was after striking out with my other two major bearing suppliers.

http://www.mcmaster.com/

They won't direct link but just search bearings, then click on ball/roller bearings, then on roller bearings, then needle bearings, and finally one way locking needle bearings.

[BrianG]

Just curoius, was anyone able to do any testing with this idea? I know I came up with the original plan, but don't have the parts...