Perpetual Motion Wood Gear Clock

This clock gives the illusion of running with "perpetual motion". At rest, it does nothing, but give the flywheel a slight spin, and it just keeps going. The entire clock movement is open and exposed, revealing no visible means of power to keep it going.

How does it work? The "floating" base is isolated from earth ground, allowing the waffle pattern to collect static electricity from the air. This is transferred to the arch in close proximity below the flywheel. Nothing happens with no movement, but when you give the flywheel a slight spin, static electricity is generated between the two - much like when you drag a comb through your hair. The interaction creates enough force to keep the flywheel moving.

Not buying that explanation?

Of course, that explanation is completely bogus. There is no such thing as true perpetual motion. This Instructables will explain how it really works.

I used a CNC by Carvewright to build this clock, and I used Carvewright Designer software to design it. I can provide the files, but as Carvewright uses a proprietary file format, they would not be useful to most woodworkers. As such, this is not an Instructable on how to just build exactly my clock, but one on how to both design and build your own version.

While many might use a CNC for a project like this, it is not required. You can, as many have on similar projects, use a scroll saw to fabricate the wheels (large gears) and pinions (small gears).

Materials

• Baltic birch plywood - lumber yard or online
• Hardwood of your choice - lumber yard or home center
• 3/16" outer diameter 3/8" inner diameter 1/8" thick ball bearings - Amazon: uxcell R166ZZ Deep Groove Ball Bearing 3/16-inchx3/8-inchx1/8-inch Shielded Z2 Lever Bearings 10pcs
• 3/8", 7/64", 1/4", and 9/64" brass tubing - hobby shop or online
• Brass wood screws (best to use non-magnetic fasteners) - hardware store
• Brass washers #6 - hardware store
• Brass washers and acorn cap nuts - hardware store or Amazon: 6-32 Acorn Cap Nuts Solid Brass 
• Brass threaded rod - Amazon: Steelworks Corporation 11505 Bolt Master 6-32 x 12" Threaded Rod NF Brass
• 3/4" diameter 1/4" thick disc neodymium magnets - Amazon: 3/4 x 1/4 Inch Strong Neodymium Rare Earth Disc Magnets N52
• Electronics - carveshop.com

Tools

• Gear design software
• CNC design software and CNC or Scroll saw
• Olson scroll saw sanding strips
• Other general woodworking tools

The clock is motivated by a variation of a permanent magnet motor, with key components hidden within its wood parts. The flywheel contains four magnets, and the arch below the flywheel contains a coil that, when energized, becomes an electromagnet. This motor will not start on its own, but once moving, the electromagnet is briefly energized just as one of the magnets passes past the coil. The magnets and electromagnet repel one another, giving a push to the flywheel to keep it moving.

An electronic circuit detects the magnet passing and applies a varying pulse of current to the electromagnet to keep the flywheel moving at the desired speed.

If you are interested, here is how the electronics works.

A key electronic component - the coil/electromagnet - has already been described. Below the coil is a Hall effect sensor. This sensor detects the presence of a magnetic field, and is used to tell when the coil is to be energized.

The heart of the electronics is a microcontroller. The microcontroller gets the signal from the Hall sensor. Looking at the oscilloscope traces, the yellow line is the active-low Hall signal, which is active as the magnet passes over the Hall sensor. The red line is the active-low power to the coil using an external transistor. You can see that the coil is activated just after the magnet has passed over the Hall sensor, giving the flywheel a push in the desired direction.

Looking at the expanded oscilloscope trace, you can see that the coil pulse width varies - at times it is short; at other times longer. This of course varies the amount of force applied to the flywheel, and is done to control the speed of the flywheel and the accuracy of timekeeping.

Power is normally supplied through an AC-to-DC wall 12V power supply, with eight 1.5V AAA cells as backup if power is lost.

(To add to the illusion, I shot video and photos before I installed the power supply jack in the clock base, and ran just on batteries. You can see the space that I left under the base to mount the jack and run wires to the circuit board in the final version.)

For those woodworkers who are also electronics and software hobbyists, I will publish an Instructable under the Electronics category detailing the design of the electronics and software. When I do, I will post a link here.

I'm going to get into gear design in detail later, but for now I need to describe the pinion gear that attaches to the flywheel, as it has a special feature. This pinion and flywheel assembly ride on a shaft using bearings. Because the pinion is rather small in comparison to the size of the bearings, it employs a larger-diameter collar into which the bearing is set.

There are several parts of the clock that use bearings. In each case, the bearings are 3/8" outer diameter, 3/16" inner diameter, and 1/8" thick. The bearings will be slid onto 3/16" brass tubing shafts. Often the bearings will not easily slide onto the tube. I use 220 grit sandpaper or emery cloth to remove a slight amount of material from the tube. If you're careful and don't clamp too hard, a drill or drill press can be used for this. Clamp the tube into the chuck and sand the rotating tube.

If using a CNC machine and it is capable, you can machine this part from 3/4" material. Otherwise, you can make the pinion and collar as separate parts, and glue them together. In that case, don't drill any holes until after assembly of the two parts.

From the collar side of the pinion, I used a 3/8" Forstner bit to drill a 1/8" recess. I then used a 1/4" bit to drill through the exact center of the pinion - the Forstner bit makes a nice centering depression. This is where the bearing will reside. Put one in its place now.

The flywheel needs to have a lot of mass, especially at the circumference, to provide inertial movement between coil pulses. The exact shape and style is not important. Even the diameter is not critical, other than the magnets should not be too close to or too far from each other. I used a flywheel 11" diameter and 1-1/2" thickness. I made up two blanks with 4 sections, using splines that would not be visible when assemble, then carved the two blanks. Of course you want to place the magnets as close to the circumference as possible. I used 3/4" diameter neodymium magnets 1/4" thick. Be sure to orient the magnets with the same pole, N or S, facing outward.

As mentioned, the flywheel runs on a 3/16" diameter brass tubing shaft using bearings at either side of the flywheel. On one side of the flywheel, I drilled a bearing recess and a hole through the center just like I did for the pinion, then put a bearing in place.

Next, I made a simple jig using a 12" square board with a 3/16" hole drilled in the center, and a 3/16" brass tube pressed into the hole. I slid the flywheel, bearing side down, onto the tube, with the flywheel flat against the board. Then I slid the pinion down onto the tube, bearing side up, with a bit of glue on the face of the pinion. This setup helps get the pinion centered on the flywheel and the bearing alignment perpendicular to the flywheel, so that it runs true. Just take care not to get glue on the tube.

There are several tools, online and downloadable, to design gear sets. Some can be used to create printed templates for scroll saws. Some can output files in formats that can be printed for scroll saw templates. Others can output file formats than can be imported into CNC design tools.

I used the Radial Vector Generator that was written by a Carvewright user and posted on the Carvewright forum:

https://forum.carvewright.com/showthread.php?17794-Make-Gears-with-Radial-Vector-Generator&highlight

(You may need to sign in to the forum to download the tool, but there is no charge to create a sign in.) This tool can generate files in the proprietary Carvewright file format, but it can also generate a format that can be imported into other CNC software.

As I wanted my clock to have a second hand, I needed a shaft that rotates at 1 RPM. It would require an extremely massive flywheel to maintain a 1 RPM rotational momentum (with 15 seconds between each magnet), so I elected to use a 12 RPM flywheel and a primary gear set of a 6 tooth pinion to a 72 tooth wheel: 6-72.

The next reduction is from seconds to minutes, a 60x reduction. I used two sets of gears, 8-80 for 10x and 12-72 for 6x.

The final reduction is from minutes to hours, a 12X reduction. I used two sets of gears, 12-48 for 4X and 16-48 for 3x. While 12x could possibly be done with just one gear set, an even number of gear sets must be used, to keep all rotation clockwise.

You can use the same gear set ratios that I did, or come up with your own.

The frame is very simple, just two pieces, front and back. The gears are stacked onto two shafts. The front frame piece attaches to the rear frame piece via the lower shaft at the bottom and a tube at the top.

The base is a single piece.

While I chose to use an arch (to mimic the flywheel design) to hold the coil and Hall sensor, the arch is not necessary. The coil and sensor can be hidden in the base if the flywheel is located near the base. The flywheel and coil must of course be in close proximity.

Likewise, the frame pieces can be as simple or ornate as you like.

For the lower shaft, simply drill a 3/16" hole in the rear frame. Press fit a 3/16" brass tube into the frame, so that tube protrudes from the back (to mount the flywheel) and front (to mount the intermediate gear assemblies).

For the upper shaft, drill a 1/16" pilot hole through the rear frame. Then, on both sides, drill a 3/8" hole 1/8" deep with a Forstner bit to make recesses for bearings.

At the top, drill a 5/32" through the frame. Then drill with a 3/16" hole 3/8" deep at the front of the rear frame. This two-diameter hole will hold the bras tube and allow a treaded rod to be inserted through to fasten front to rear frames.

The front frame likewise has 5/32 - 3/16" holes top and bottom, with the larger partial drill from the back side. The middle hole is 1" diameter, drilled from the back of the front frame with a Forstner bit, 1/2" deep. Then, drill it through with a 19/64" drill bit.

A flywheel constructed of wood may not be in balance because of varying density of wood, or a slightly off-center shaft hole. With it mounted on the frame I gave it a bit of a spin, and watched what happened when it slowed down. It needs to rotate freely, which is should on the bearings - the 1/4" hole through the center of the assembly should easily clear the 3/16" shaft, so only the bearings are at work. If not in balance, as the flywheel slows it will rotate back and forth and settle at the heaviest point. I used masking tape and various bits of metal applied to the opposite side to retest and find the location and correct amount of balancing weight needed to see the flywheel stop spinning without significant backwards movement. I cut a piece of brass of approximately the same weight as the temporary counterweights, a bit oversize, then trimmed and retested until the balance was pretty good - it doesn't have to be perfect.

This would be a good time to test operation with the electronics, before going on to design and build the rest of the clock. Note that the polarity of the coil, when energized, must be the same as the magnets - flip the coil over if necessary.

I used bearings for the rotating parts that are moving faster - the flywheel and the second hand shaft. I used bushings elsewhere.

The brass tubing is sized so that the next larger diameter slips over the next smaller one. For example, a 7/32" diameter tube slides over a 3/16" one. The lower shaft is 3/16" tube, so gears that rotate on that shaft can use a 7/32" tube as a bushing.

The lower shaft is a 3/16" tube, pressed into to the rear frame. The flywheel uses bearings and is located on that shaft at the back of the frame. The intermediate gear assemblies on the front of that shaft use bushings.

The upper shaft is a bit more complicated, consisting of three rotating shafts, one over the another, for seconds, minutes, and hours hands.

At the center is a 3/16" second hand shaft. It is attached to a wheel on the back of the clock that is driven by the flywheel. It passes through the frame on two bearings. A pinion gear is rigidly attached to it. The shaft extends to the front of the clock all the way to the second hand.

Over that is the 1/4" minute shaft. A pinion is at the back end of this shaft, and the minute hand at the front. Note that the pinion and minute hand both use bearings to the second hand shaft. Also note that the 1/4" shaft does not touch the 3/16" seconds shaft, as it is two sizes larger, so the only point of contact between the minute and seconds shaft is the bearings.

The 9/32" hour shaft slides over the minutes shaft, and essential acts as a bushing between the two shafts.

To allow the correct time to be set, the minute hand pinion and shaft is coupled to the movement with a clutch. The clutch is spring loaded such that the entire minute hand shaft assembly slides axially a bit on the seconds hand shaft to make contact with the rear clutch face. This means that the bearings in the minute hand shaft assembly must be able to slide fairly freely on the seconds hand shaft.

I machined 60 teeth in the clutch faces, so when setting the time, the minute hand will click into place for each minute. If you're not able to do this, a high-friction material such as felt could be used.

Spacers cut from brass tubing one size bigger than the shaft onto which they are located are used in a few places to keep the parts in alignment.

Note that some gear assemblies, such as the two on the lower shaft, have long bushings, in essence built-in spacers.

Starting with the minutes shaft, drill a 3/16" hole 1/8" deep with a Forstner bit into the clutch face side of the minutes pinion. Then drill through the center with a 1/4" drill bit. Press the hour shaft in from the front side, securing with adhesive as needed. Install a bearing.

There are two 72 tooth wheels, two 48 tooth wheels, and two 12 tooth pinions, but they are different diameters because they mate up with different wheels and pinions. Pay attention!

Glue the other clutch face onto the smaller diameter 72 tooth minutes wheel. From either side, drill a 1/16" pilot hole through the center of this assembly. Then, using the pilot hole, drill bearing recesses as before with a 3/16" Forstner bit. Finally, drill through the center with a 1/4" bit. Install bearings front and back.

Drill 7/32" center holes through the 80 tooth wheel and the smaller diameter 12 tooth pinion. Press a 7/32" tube through the pinion, apply adhesive to the pinion face, then press the pinion and tube onto the wheel until they meet, and clamp. You should have 3/16" of the tube protruding from the wheel, and 1/16" protruding from the pinion.(This may vary depending upon your construction. These dimensions may be different for you, to get proper alignment between the gears on the seconds, minutes, and hours shafts and the intermediate gear assemblies.)

Repeat the process for the minutes-to-hours smaller diameter 48 tooth wheel and larger diameter 12 tooth pinion, with just 1/16" protruding from either side.

The seconds assembly is made with the larger diameter 72 tooth wheel and a 1-1/4" hub. I drill a 3/16 hole in each, use a scrap 3/16" tube to align, glue and clamp, then remove the scrap tube.

The hours assembly is made with the larger diameter 48 tooth wheel and a 3/4" diameter hub with a 9/32" center hole.

The seconds hand shaft is press fit onto and through the pinion, with the pinion located in the proper position. Secure with cyanoacrylate adhesive if needed. Note the spacers in front and on the back of the pinion. Install this into the frame using a bearing.

On the back of the frame, press fit the 72 tooth seconds wheel onto the shaft. Using a spacer, install the flywheel onto the lower shaft.

Next, install the seconds-to-minutes intermediate gear assembly onto the lower shaft.

Install a spacer, then the 72T minutes wheel with clutch and two bearings.

Install the minutes-to-hours intermediate gear assembly onto the lower shaft.

Install the minutes pinion/clutch with bearing and minutes shaft.

Install the spring, followed by the front frame. Press fit the hour hand, minute hand with bearing, and second hand, aligning all at 12 o'clock.

Slide #6 brass threaded rod through the lower shaft and upper tube, and secure with brass washers and cap nuts.

The wheels and pinions must mesh with as little friction as possible. I use a simple jig to test this. Correct any problems with wheel and pinion pairs before assembly. I use Olson scroll saw sanding strips to finish wheels and pinions. It's OK if the wheels and pinions have a lot of backlash, or slop, in them - better that than binding.

The wheels are quite large. Shafts must be perfectly perpendicular to the wheels, or the wheels may wobble and interfere with other parts.

Test fit the locations of parts on the shafts, and verify the lengths of shafts, before gluing anything in place.

Test operation of the clock often as you assemble, adding movement components one at a time, to isolate any problems.