The impetus for this idea was Joe Johnson's post
here.
It is not finished such that it could be immediately manufactured. As such, there is but one screenshot illustrating Joe's idea taken to its logical next step, I think, and a discussion of what's missing, the advantages and drawbacks, and, with luck, ideas for improvement.
The goal was to design a transmission that does not require meshing gears or shifting dogs. Chain and sprockets are accessible to most teams, so I imagined that a transmission design like that illustrated by Joe Johnson and again here might be something to strive for.
Shown, this is operating in low gear, with the black line representing the path of the roller chain. The part not shown would be a mirror of that which is shown, less the red, triangular carrier. The shifting mechanism is not shown, but discussed later. It would be fixed to the carrier. The purple shaft is the input and pivot point of rotation of the carrier.
It is currently geared, due largely to my laziness in trying to find gears, for 3:1, 1:1, and 1:3. Any three ratios that maintain the same center-center distance would be appropriate. The chain represents an additional 2:3 reduction to the wheels.
Advantages- Stripped of my predilection toward fancy, unnecessary shapes (i.e., the tri-star carrier), it can be built with a simple mill.
- Roller chain is more forgiving about meshing and alignment, reducing the precision required in, at the very least, some of the machining work.
- The three gearsets remain engaged 100% of the time
- Considerably simpler than other 3-speed transmission designs because it requires only one shifting mechanism per side like many 2-speed designs.
- Final ratios are easily changed by altering wheel sprocket
Disadvantages- Can't shift while the chain is in motion, lest Bad Things (tm) happen.
- Requires a motor to shift the transmission, both due to the need for unimpeded rotary motion and the need to balance against the tension of the chain that will try to rotate the carrier.
- May be slow to shift due to the gearing needed to achieve the above.
- Three speeds is probably overkill, but you never can tell.
- It still requires considerable gearing before the input into the carrier.
So, that's that. I'm still working on packaging these things for upload (the two-speed chassis I posted previously as well) -- but, discussion is, of course, welcome.