https://grabcad.com/library/inverted-2-speed-gearbox-1
Here is my concept of a 2 speed, 2 stage, 2 cim, inverted gearbox. I have seen 2 speed inverted gearboxes before on here, but they were all 3 stage, so i wanted to make one with 2 stages to save space and increase efficiency.
The high speed is 14.79 fps(6.29:1) and low speed is 7.32 fps(12.71:1), using a 4 inch diameter, 1.5" thick colson wheel
The dimensions are ~7.625" along the frame rail, ~4.75" from the inside of the frame rail to the output shaft of the cims, and ~3.5" from the top of the frame rail.
The shifter block has to be drilled out and threaded to a 5/16" male size thread for the pancake cylinder, due to there being no 1/4" male thread output option for pancake cylinders.
Using the WCD bearing blocks to attach the gearbox gave just enough space for the shifting cylinder to have enough clearance with the wheel.
The shifting block is COTS from andymark, though more space could be saved by using a shorter shifter ‘stick’ and a shorter stroke cylinder. My team has made our own custom shifter ‘sticks’ and it was quite the hassle, due to the small size.
There is a built in encoder into the design, where it is attached via timing belt to the output shaft. There is the possibility to attach it to the back side of the output shaft, but that adds to the overall length.
To get these gearboxes out of the robot requires only taking off the 2 bolts of the bearing block along with taking off the wheel.
There is also a similar configuration for 6 inch wheel by using larger output gears, but I have only run numbers for speeds, not spacing.