Furious Tourbillon
Introduction: Furious Tourbillon
I modeled this design after the tourbillons in the Jacob and Co. Twin Turbo Furious watch. I spent many hours looking at this video.
I tried to make the model an accurate (scaled up) version of the original Furious mechanism. I printed the screws to scale and used them as caps to cover the 2mm screws that actually hold it together. In looking at the videos of this design, there mechanism with a spring between two plates (shown below). I'm don't know what its original intent was, but I'm using it to decouple the intermittent rotation of the movement (you can see the balance spring below the trellis) from the constant rotation generated by the stepper motor. Without it the L2 spherical frame would jerk with every tick. The spring and the lower silver plate attach to the movement assembly. The end of the spring is attached to the upper silver plate with that Philips head screw, which is driven by the motor. And there is a pin below the screw that sticks into the slot in the lower plate. In the picture the assembly is at rest, so the spring has pulled the pin to the right end of the slot in the lower plate.
When I turn on the stepper, the end of the spring slides in the slot to the left, and the spring passes torque to the (L1) movement assembly so it can tick. When the speed of the motor matches that of the movement, the pin of the end of the spring moves back and forth in the middle of the slot. If the speed of the motor is slow, then eventually the pin moves to right end of the slot and the movement stops ticking. If the speed of the motor is fast, then the pin moves to the left end of the slot. 949
When it hits the left end of the slot, there is a step function in the torque and the things can go bad very quickly.
This is because there is a torque overload when the end of the slot is hit, the torque overload passes too much energy to the balance wheel (sort of kicking it) causing to swing further, which reduces the tick frequency and average rotation rate of the movement assembly. The symptoms are that the movement suddenly starts ticking very loudly, and the movement quickly binds. The sudden drop in the rotation rate of movement aggravates the overload condition, which if ignored can break shafts or teeth of gears. The one time I didn't stop the motor in time, the main shaft sticking out of the L1 Frame Bridge broke.
I can watch the watch the position of the pin in the slot as it goes around, and tweak the motor speed to keep it centered. The problem is that there is a huge delay in the response time to changes in motor speed, so it's easy to over correct and lose control.
The code using sets the initial speed very low, so when I turn on the stepper, it starts at a really slow rotation rate and this design needs a much faster rate. So I have to crank the shaft encoder like mad to get it up to the speed, and at the same time I bump the balance wheel to make sure it doesn't hang and break some gear teeth or something else. So for all practical purposes, you have to kick start it like an old hit-or-miss engine, then carefully tend it to keep it running. I actually found it sort of a challenging to find the speed sweet spot. So I decided to post the design as is, explain the issues, and see if anyone comes up with a solution.
Other learnings...
At one point I squeezed the outer edges of the L2 Upper and Lower Bodies together too hard, and I broke the shaft sticking out of the L1 Frame Base. My solution to this and the L1 Frame Bridge shaft breaking was to design a 3mm hole in the center of each shaft, that I could slip a 3mm steel rod into.
This was also my first experience with 'silk' PLA filaments, and there was learning curve. Using the same settings that I have been using forever for regular PLA, the first layer didn't want to stick to the print bed, and I found that it has relatively poor inter-layer adhesion. To address the layer 1 problem I tried changing the print bed temp from 60 to 70 C°, but it did not seem to be very effective. What worked was a lower the Z height on the first layer to get a lot more squash to it. To address the inter-layer adhesion problem, I turned up the extruder temperature 10, but again this did not make a big difference, however the parts seemed a little stronger when I changed the perimeter layer count from 2 to 3.
A lot of people complain because silk filaments clog their nozzles. 215