After finishing the article on the compound Pendulum for the Woodenclocks website I need to validate the calculations from the Excel file I had been using. It has taken a while but I finally built a rig to test the calculated results, based on the engine used in a metronome. It's the only mechanism that I could find that actually used the compound pendulum so turned out to be ideal for 3D printing the rig. The rig is driven by a weight inside the steam engine style boiler on the end of a stalk, it drives an escape wheel through a gravity ratchet and a couple of gears to give around 2.5 minutes of running time. The compound pendulum controls the rate at which it tick-tocks , moving the top weight up slows down the pendulum and visa verse. The top and bottom weights can also be changed out for bigger or smaller weights to also change the rate. With all these possible variations it was straight forward to finesse the results to get the right combination that could be scaled for use in a larger wooden clock.
This rig could also be modified to add a scale so that it could actually be used as a metronome, as it is it's actually a nice little gadget to create on your 3D printer.
Files and video are available by clicking on the image to the left.
Printer: Zortrax M200
You will need 1 of each STL part except for the following:-
Spacer 3 requires 2 parts
Pawl requires 4 parts
Wedge requires 3 parts
Escapement requires 2 parts to be solvent bonded back to back
You will need some extra components to complete the build :-
6 roller bearings Ø2mm x Ø6mm x 3mm
1 piece Ø1.5mm steel rod for the pendulum
1 piece Ø2mm steel rod for the pendulum pivot
2 piece Ø2mm steel rod for the gear shafts
Acetone to solvent bond the frame and other parts together.
Ø9.5mm steel balls (Catapult ammo) for the weight.
Ø12mm Brass rod for the weights Or washers, 8 grams for top weight and 23 grams for the bottom weight.
Magnet Ø5 x 5mm long to hold the top pendulum weight in position.
STL files for download are in 3 groups Blue, Red, and Orange, Use the drawing opposite as a guide for where the components fit into the assembly.