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Made my large moon clock electric

So I finished the clock and everything was great until my son said that the ticking was driving him nuts (his room and bed is directly above on the same wall)

So after some time in CAD i came up with a stepper modification to turn the clock electric. The goal was a "plug and play" board that I could adjust to get the right RPM. In hindsight, Steve's board probably would have been more accurate and easier but here we are.

I started with this board: https://www.electroschematics.com/mks-osc-stepper/ I configured it in the lowest Frequency mode

For the driver I used a TMC 2209 in 1/4 step mode (produced the quietest results). The board was mounted in one of these: https://www.aliexpress.com/i/32848685464.html

The stepper is from an old 3d printer and the gear is just a remix from Steve's gear.

The whole contraption runs off 12V and I used a 12V to 5V step down board to get the 5V need for the driver.

It is now quiet as a mouse and I get the moon phases!

3 comments

3 Comments

Stu Harrison

Jun 20

Yes with regards to timing it seems to speed up and slow down over the course of day--the next effect is to be off by a couple of minutes either way each day. Since I'm really happy with the look of the clock and its virtually silent, I can live with it for now. I agree on the pendulum and I was trying to come up with a way of keeping it without making any noise.

Aside--it looks like I need that 12T gear to rotate at .658RPM (is my math right?)--once I get an arduino to do that exactly, I might swap out the electronics.

Steve

Jun 20

Replying to

It seems normal for it to drift around based on temperature.

My first stepper motor clock used an Arduino Nano to directly control the rate. The Arduino Nano has a ceramic resonator with a specified accuracy of +/-0.5%. It is relatively stable over time, but each clock needed to be calibrated to offset the initial error. One Arduino might be 0.3% fast and another might be 0.1% slow. That is why I switched to a precision real time clock reference for my newer designs. They have internal voltage and temperature compensation to stay accurate within about a minute per year.

Your math seems close. That clock has 3 sets of 12 tooth pinions driving 54 tooth gears.

(54/12)^3 = 91.125 rotations per hour = 1.51875 RPM = 0.658 MPR (minutes per rotation).

Steve

Jun 19

That is super cool. The ticking sound is only acceptable in certain locations. I don't mind it in my office next to the 3D printers, but they cannot be next to my bed or in the TV room.

It appears that the stepper controller uses a 555 timer. It must be tricky dialing in an accurate rate and getting it to maintain that rate.

You got me wondering if there is a way to add a lever arm to silently drive the pendulum. The motor would do all the timekeeping, but even a dummy pendulum makes the clock look better.

Steve