As a first step of a robotic arm project, I wanted to design and manufacture a speed reducer that would increase the torque output of my NEMA 17 stepper motor while also being compact. That is how I started to learn about cycloidal drives. As a first step, I decided to 3d print a prototype cycloidal drive version, to learn about different design constraints. I first decided that I wanted a 9:1 transmission ratio, so that meant I needed to use 9 lobes on the cycloidal disk, and 10 pins. I started off by designing the cycloidal disk:
This disk profile was generated using epitrochoid parametric equations along with the following parameters: 45mm pitch diameter, 10mm roller diameter, N = 10 (10 rollers), and 2mm eccentricity. Next, I made holes for the input shaft and the output pins. I also designed another version of the disk, where the holes were 180 degrees out of phase for alignment purposes.
Next I designed an eccentric output shaft so that I could align the two disks exactly 180 degrees out of phase of each other. This is what it ended up looking like:
I also designed a drive housing that would serve the purpose of holding the shaft in place and the rollers for the drive to slide on (the pitch diameter for the rollers was a design parameter that was used to develop the gear profile):
Finally I designed an output shaft object that would help indicate the rotations of the drive output. The diameter of the output pins was chosen carefully to be equal to the output pin hole - 2 * eccentricity for alignment purposes.
Then, after a few iterations, failed designs, and many SolidWorks motion studies like the one below I was able to assemble a functional cycloidal drive prototype.
It is possible to see that 9 turns of the input crank result in one turn of the output, and this is the desired transmission ratio based on the number of lobes and pins!
The next stages of the project will be converting this design into a more precise and efficient design using bearings and bushings for low friction contact and stability. And including a motor mount so that the input can come directly from the NEMA 17 stepper motor.