pic: what do you think?

[kmcclary]

Originally Posted by JVN

How will you get the pneumatic to go to 3 different positions?

Easy...

1) Stack two identical short throw pistons along the same axis, on something resembling a drawer slide. (One piston's shaft pushes the next piston's back end.) If placed on the same side as in the drawing, in-in = 1, in-out (or out-in) = 2, out-out = 3.

2) A variant of (1): Make one piston's length twice the other. You now can switch between four gears. However, switching between gears 2 and 3 without hitting 1 or 4 MAY be difficult.

3) Another way to couple two cylinders is the "square Y" configuration. Place them parallel to each other. Add a simple flat bar as a linkage between the two clevises (clevi???). The two cylinders and the link bar forms the "U" part of the "Y". The gear throw rod is then attached somewhere in the middle of the crossbar with another clevis, forming the lower tail of the "Y". By varying the stroke length ratios, and where you connect along the center crossbar, you could even have a similar situation as case (2). BTW, You'll either need to allow the cylinders to swivel from the back end, or one side of the crossbar needs to be a slot, to make this work. Otherwise, it'll bind up and probably bend a cylinder shaft. This method lends to better packaging: "Fold it over", one cylinder on top of the gearbox, one on the bottom. (Now it is a "W" linkage...)

You really should check out Team 33 (Killer Bees). They have a very tight "binary" FOUR speed "autoshift" gearbox this year, made out of only two plates, shafts, chunks from only a couple of different gear sausages, and two cylinders. VERY simple. Theirs had the two pistons in separate places. By placing an encoder disk on the wheel, the software could even autoshift it for them at predetermined speed points. They said it keeps the motors running at near peak efficiency over a LARGE speed range. IMHO, VERY cool. They said once the parts were cut and the plates drilled, it only took ONE student ONE night to assemble the entire thing.

They may be putting up a Whitepaper on it soon. (One can only hope!)

- Keith