Here is my DIY butterfly capacitor motor drive design.
With five dollars worth of plastic and a three dollar stepper motor, I am hoping this works for remotely tuning the capacitor of my magnetic loop antenna.
As described previously, my goal is to be able to fine tune this antenna from a distance. This means sending signals from my ham station to turn the capacitor using a stepper motor. To get fine tuning, I will try to use a worm and worm gear which will provide a reduction drive.
At this point in the project, I am truly “making it up as I go along.” Not being an engineer, I know that I am out of my depth. While I used some design software for creating the worm gear set, I really have not a clue whether it will fit together properly. My biggest concerns are whether or not I have left enough adjustment slack so that the parts can be aligned, and whether I can get away without proper bushings. Will a plastic shaft turn smoothly in a plastic hole? Will the friction between the worm and the worm gear cause melting without lubrication? Will the whole thing just fly apart the first time I power up the stepper motor?
Butterfly Capacitor Motor Drive with Plastic Parts
One of the neatest things I have learned to do with 3D printing is designing for “captive nuts”. This means making hexagon shaped holes in the surface for holding a nut in place. The design shown above uses M2 screws with captive nuts for mounting the stepper motor and the end stop switch. It also uses M3 screws with captive nuts for holding the worm in place.
Oh yes, the design includes a mechanical end stop switch. I will attach a plastic bar to the threaded rod so that I can activate the switch. This means being able to “home” the capacitor to its minimum position remotely.
This drive section is designed to be zip tied to the PVC pipe, about 18” away from the capacitor. A flexible coupling will be used to join the brass rod from the capacitor to the rod from the motor. Flexible couplings can accommodate a slight misalignment between the two shafts.