I chose the 32 pitch .500 bore aluminum hub gears in the following sizes: 48, 64, 72 & 76 teeth. I also selected a pinion with 11 teeth for the motor shaft.
To begin, I turned some 6061 aluminum down on the lathe to an outside diameter of 3.270 x .500 thick; I also bored a .500 hole in the center
I knew there would be several different operations for the CNC so I machined out a set of soft jaws for the vise so the stock could be clamped easily without having to find the center each time I load a different part. For the 14mm holes, I chose a .250 end mill cutter. A rough cut is made then a cleanup cut completes each hole. The CNC interpolates each hole so using the same cutter; I can make almost any size hole I need.
With the stock mounted, I ran a basic pocket program to hollow out the hub. Once again a rough cut followed by a cleanup cut leaves a nice finish.
Once the piece was pocketed, I was ready for some details. Below is a screen grab of the CAD program on the left and the CAM G-code on the right. The CNC will use the G-code to machine the part.
I double checked the tool path and then let the first program run. The 14mm hole at the top is closer to the sidewall so I machined deeper to allow clearance for the pinion.
An additional program drilled all the holes I would need.
The completed piece turned out almost perfect the first time. I also ran a program to machine ServoCity’s .770 mount pattern so the hub would be easy to attach.
Using the 64 tooth gear, I attached the gear to the wheel and assembled the pieces.
Using the same 11 tooth motor pinion and moving the motor to different positions on the hub, I can run the ratio that works best for any projects I want to build using this wheel. Numerous motor ratios are available from 26 RPM to 2,737 RPM. These particular motors have the encoders already attached for feedback. Here’s a picture of the finished unit:
I had to add small spacers to each motor to adjust the depth of the motor shaft. I don’t like cutting the shafts of motors so the spacer is a good choice. Here’s another picture of the finished units along with a set of prototype units with brushless motors just for fun.
Stay tuned for more from David Nyman.