Waving Mechanism for Stage Prop, Decoration, Moving Sign, etc. by SteveJohnsen

Last crawled date: 3 years, 4 months ago

This is designed to mechanically produce a waving motion, driven by an electric motor. It is designed for a stage prop that has a cartoon figure in a window who is waving out the window. The design is for a specific purpose, but it could be used for other purposes, such as Halloween or Christmas decorations, or for moving signage.
If printing with FDM, for stronger pieces print in the orientation in which the object files are oriented in the object file. This will best utilize the filament flow and layering.
Each assembly requires two arm connectors to be printed.
There are three lengths of pivot brackets, which control the throw or width of the waving arc; the shorter the bracket, the longer the arc.
The arm connectors are designed to hold the rod, which is a segment of a wire coat hanger, but allow for easy removal of the rod or repositioning of how far the rod is inserted into the connector. This is helpful for adjusting the length of the rod or the distance between the two arm connectors, which determines the position of the waving motion.
The axle is a standard 8D nail (U.S.). It passes through the pivot bracket, prop arm, pivot backer, and into the window frame. Drill a hole that is nearly the diameter of the nail that you are using. 1/8" is slightly too wide for a standard 8D nail. The nail should fit in the hole snuggly, but not so tight that you have to hammer it in. If the nail is pounded in and you ever need to take apart the assembly, it is difficult to remove the nail axle without damaging the pivot bracket. Also, be careful not to insert the nail too far; this will cause the mechanism to bind due to excessive friction. The prop arm should pivot freely, but not be sloppy. The 8D nail can be cleaned up and be made smoother by removing any machining/stamping marks or burrs near the head of the nail.
The motor arm piece is designed for a specific "D" shaft motor that I happened to have. Since there are many different styles and dimensions of motor shafts, you may need to modify this piece to fit your motor shaft. The speed of the waving motion is determined by the RPMs of your motor; the range of most human waving would be ~30 to 120 RPM. Since there are no gears, the ratio of RPMs-to-waving cycles is 1:1.
Lightly sand the clip posts on the motor arm and pivot bracket that clip into the arm connecters so that they are smooth and so that the arm connectors spin freely. This is not essential, but it will reduce a bit of friction and a minor amount of strain on the motor.
The pivot backing is designed to glue to the back of the prop arm and provide additional support to keep the prop arm perpendicular to the axle. The four holes in the pivot backing are to allow additional gluing strength; I am planning on putting a glob of hot glue in each hole to form a tack weld of sorts.
The pivot bracket is also intended to be glued to the prop arm. There are two screw holes on the side of the pivot bracket so that it can be screwed to support/stiffening material on the prop arm. If screwing the bracket to the support material that is already fixed or glued to the prop arm, there is no need to glue the bracket itself to the prop arm. The two screws will hold sufficiently in most cases. The pieces can also be taped instead of glued if not waving at high speed.
The design is scalable. You will, however, need to modify the hole in the motor arm to fit your motor's shaft, after you have scaled the model. You may also need to do some modification to the connector arms so that they clip nicely to the connecting rod that you plan to use. When scaling, obviously you will need to scale each individual piece to the same scale.
BTW, in case you are wondering, the photo with the actual assembly is only an ugly mock-up arm that I quickly cut out of core board for prototyping. :D