pic: Drivetrain Concept

[echin]

The center wheel uses a rod running vertically through the side cross pieces of the frame and the 1/4" aluminum plates. Four springs would attach to a tabs on the top gusset of the cross piece at each corner and the bottom attachment plate on the center wheel module. The plates should flex a little and allow the wheel to maintain constant contact with the ground, and because of the springs, there would be little force pushing up on the cross pieces to bend them, but it would probably be better to change at least one set of the cross piece gussets to 1/4".

For the outside U channel pieces, I was planning on using a structural bumper mounting system consisting of long pieces of box tubing bolted to the frame along its entire length, which would be attached to the plywood of the bumper. This would essentially turn the outer frame pieces into pieces of box tubing without adding the extra weight. For the inner frame pieces, I will switch them to the .1" Vex tubing or 1/16" tubing. How much would increasing the length of each leg of the T shaped gussets on the frame increase the rigidity? It seems like that would improve the rigidity by a fair amount, but I have not made a frame using gussets before, so I have no experience with that.

I was planning on adding some kind of spacer between the two side frame pieces, but I want to be able to easily remove the outside piece to more easily take off CIMs and wheel modules, so I haven't come up with a good way of doing that yet that wouldn't require sheet metal or welding, which we can't do.

To make the wheel module shafts easier to line up, I was planning on latheing down the ends of the shaft to slightly under 1/2" and rounding the edges, then using round bearings. That would cost less and be easier to line up.

To change the maximum speed of the drive, I would just change the ratio using a different reduction in the sprockets. Since we will hopefully try building this drive before the start of next season, I wanted to make it easy to adjust so that we could try different confiurations and possibly adjust during the build/ competition season if we needed to. I set the speed at 20 fps because it seems like it would never be reasonable to gear faster than that.

The CIMs do not touch any of the bearings (that's one of the reasons the gears are the size they are), but if I were to use smaller gears, I would lathe down the end of the gearbox shaft to 1/4" or 3/16" so that the bearings could be smaller (that's what I did on the center wheel).

Hopefully, we will actually make this drive, so a lot of the design is based on our machining capabilities. We have access to CNC/ manual milling machines at our sponsor's shop, but in house, the only metal working stuff we have is a drill press, a small lathe, and a horizontal band saw.