Sleeve design change
Alright. We were having a lot of trouble trying to come up with a design for the gear shifting, since it is extremely difficult to create a device that would move the outer sleeve in discrete steps in both directions without requiring an overly elaborate apparatus.
To solve this, we changed the sleeve design a little. The new inner and outer sleeves can be seen in Figure 1.
In the figure, the axle passes directly through the section shown. This, of course, is connected to the cranks and will be turning. Directly surrounding this are the two sleeves, which remain stationary relative to the frame. The inner-sleeve can be seen attached to the bottom bracket on the frame (I’m not sure if this is the best way to do it, but it will do for now). The grooves on the inner-sleeve have been changed to spiral along the surface of the sleeve. Slots have been added to the upper-sleeve. Therefore, when the upper sleeve is turned, the bearings will slide along the path of the lower-sleeve.
This means that the upper-sleeve no longer slides. It simply twists. This simplifies the gear-selection problem greatly. Additionally, now, provided that the outer-sleeve is held in place, the ball bearings will be locked in their location along the shaft. This reduces the chance of accidental sliding of the bearing.
Several changes need to be made to the overal design as a result, but they are minor.
Changes which must be made to Figure 2 are:
-The upper-sleeve must extend as far as the lower-sleeve.
-The part of the arm which slides to give the 1:1 ratio must not be pushed into place by the edge of the sleeve, but by the actual ball bearing. This is not a problem, since the grooves now extend that far
-Since the sleeve no longer has to slide, all of the space on the left hand side is suddenly freed-up. There is even the possibility of putting another planet-sun combo in the extra space, but let’s not get ahead of ourselves.
So basically, we’ve converted the gear-shifting issue into a simple matter of rotating the upper-sleeve. The amount of the rotation per gear will depend entirely on the pitch of the grooves in the lower-sleeve. There is ample room between the frame and the edge of the hub for some device to control the rotation. It basically just comes down to preference now. What would people like to see controlling the rotation? Some kind of ratchet? Bike cable and grip shifter?
As an aside: All the comments about gear ratios are duly noted. I don’t know if we’ll have time to make the changes for this presentation, but the lower step ups might be a good idea.