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I built my first cauldron creep this year, and while I'm perfectly happy with the smooth circular motion of the stick in the cauldron, I wanted to try something a bit different. Thanks to Ptolemy and his successors and their use of epicycles to try to model the universe, I have created a relatively simple system for making a more complex stirring motion. I call it the Epicyclic Stirring System.

Here it is in action. Notice how the point at which the stick is closest to the side progresses around the tub.


I doubt I'll use it this year, simply because I only have one cauldron creep and that one already has a "floating bones" cauldron. This won't work with that design because there's too much movement of the stick. Maybe next year I'll make another creep and use a cauldron with just lights and fog.

There are some things that could be done better, and I'll mention those at the end.

Now on to the build! I hope this is clear--I'll be happy to answer questions or fix the confusing places if it isn't.

I'm not going to bother you with detailed measurements, because you want it to fit whatever cauldron you're using. The key measurement is this: From the center of the main axle to the outermost part of the cup when the arms are fully extended must be just less than the radius of your cauldron, otherwise you'll scrape the sides. The length of the arms is thus entirely determined by the size of the cauldron you're going to put it in. Ditto for the size of the plywood base.

So first, you need a motor. I'm partial to the TYC-50 you can get on eBay from China for about $5. It's small, has good torque, and it's quiet. I used one that spins at 5-6 RPM. Mount that to a piece of plywood. Notice in the image below that I've drilled a shallow hole for the wires to come out. THIS IS IMPORTANT because if you don't, the wires will likely get pinched against the motor body and short out--I speak from experience.

Next you need to add a couple of small blocks of wood to support the main pulley. Notice their placement in the images below. This is also important, because you're going to attach a drive shaft onto the motor shaft, and you're going to use a cotter pin to do it, so you need access to both sides of the hole in the motor shaft.




The main pulley itself is made of three pieces of plastic. I used a plastic cutting board from Big Lots and a hole saw set. The outer circles are 3.5" in diameter, and the center circle is 2 5/8". Each has a 9/16" hole in the center. Glue them together with PVC glue. In the above images, I have the main pulley attached to the blocks with liquid nails. This did not work. You'll need to screw it down, but make sure to drill pilot holes and keep the screws inside the center part of the pulley--don't want them to interfere with the rubber band.

While you're at it, you might want to make the smaller secondary pulley. The outer circles are 1 1/4" and the inner one is 1". The center hole is 1/4". You may also need another plastic washer later, so cut another 1" circle with a 1/4" diameter center hole.

Here's a shot of the completed mechanism. I'm going to refer to it during the rest of the tutorial.



Now let's make the drive shaft. Cut a piece of 9/16" oak dowel (you can use poplar or pine, but it won't be as strong) a few inches long. It simply needs to extend through the main pulley and the thickness of your primary arm. It's can't extend much above that, or it will interfere with the outer rotating arm. You'll see that mine is cut flush.

The drive shaft needs two holes. First, drill a 17/64" hole in one end. This will allow the drive shaft to slide down over the motor shaft. Next, measure up from that end about 5/16" and drill a 1/8" hole halfway through the dowel. Slide the dowel over the drive shaft, line up the hole you just drilled with the hole in the motor shaft, and drill the rest of the way through. Leave the dowel on the motor shaft for now.

Now cut a main arm from some plastic or lightweight wood (pine, poplar) or aluminum. Mine was 5 1/8" long, and about 1 1/2" wide. Drill a 9/16" hole close to one end, and a hole just slightly larger than 1/4" (I used the same 17/64" bit from earlier) near the other end. Using wood glue, glue the arm onto the drive shaft. Since everything is in position, you can push the arm down onto the shaft so that it just barely touches (if that) the main pulley. Once the glue is dry, you can trim the shaft. If you want, you can attach the shaft with the 1/8" cotter pin now. Just line up the holes in the drive shaft and motor shaft, push it through, then bend the legs out and around the drive shaft.

The axle for the outer arm is a 1/4" bolt with threads all the way along its length. I believe mine was 2 1/2" long. Put a washer on the bolt, then apply a liberal amount of liquid nails. Slide your secondary pulley onto the bolt and allow the glue to dry for a day or so.

While that's drying, you can make the outer arm. Mine was about 4 1/4" long by about 1 1/2" wide. Drill a 1/4" hole near one end, and attach your cup on the other end. I used a 1" x 1/4" bolt to attach mine. Again, make sure that when the entire thing is assembled and the arms are at full extension, that the total length is less than the radius of the cauldron.

When the glue on the axle is dry, add a flat washer and stick the axle through the 1/4" hole in the outer arm. I added a plastic washer here (made from the same cutting board) in order to give the outer arm a bit more clearance from the main arm. Add another washer. Next, put a 1/4" nut on the axle, and spin it down to a point just above the washer. It should not touch the washer or be tight in any way. Put a 1/4" lock washer on next, then put your outer arm on the axle. Add a small washer and another 1/4" nut. At this point, you need to hold the first nut (the lower one) in place with a wrench and tighten the upper one with another wrench. If done correctly, the two nuts will squeeze the arm between them. The lower nut must rest lightly on the washer just above the plastic washer. In other words, the secondary pulley and the arm should be firmly attached to the axle (one with glue, one with nuts), but the axle and the washers should be able to spin freely.

Next, find a rubber band or two that will fit over your pulleys fairly tightly. You don't want it to slip, but you don't want to have to use the Jaws of Life to get it on, either. You can see that I actually used two rubber bands. It seemed to work a bit better than with just one.

Now wire up the motor, and you should be in business!

I added a couple piece of 2x4 to the bottom of my plywood base because I anticipate pumping fog in beneath the base. That should even out the fog as it rises.



I said earlier that there were things that could be done better. First and foremost, a sprocket and chain would be much superior to pulleys and rubber bands and would make for a much smoother movement. I didn't have those on hand, though. A better rubber band (wider, thicker--maybe like what you find holding broccoli together in the grocery store) would probably smooth out the movement, too. Instead of just putting the bolt through the arm and letting it spin, a small piece of pipe could be used, with the axle turning within it. Maybe I'll mess around with these changes for next year, but anyone who wants to try your hand at it, be my guest!

I think that about covers it. Let me know if I can clarify anything.
 

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