Square mystery clock - Can you guess how it works?

Square dial mystery clock.It does not have transparent rotary disk because it never fit in the frame. Can you guess how it works? Of course, it has a motor at the bottom. The question is how to drive the hands through transparent glasses.

Please google with the words "square mystery clock" to see the original antique fancy clocks in mid-19th to early-20th century.

Update Feb 24, 2021

• Arduino code for stepper motor control is improved. Rotation is a bit smoother than before, with 8-phase control.

Mechanism

Mechanism is revealed in the video below.

Assembly ========

You need

• all 3D printed parts except the file named "optional"
• acrylic plate (plexiglas), thickness is around 1.6mm, 160x156, 160 x 190mm
• 28BYJ-48 stepper motor with driver amplifier board
• Arduino nano
• Tactile switch (fast forward button for time adjustment)

Fix front glass to the frame-front.stl with adhesive tapes.

Adjust the balance of hour.stl with nuts as a counter weight. Please take a look at
https://www.thingiverse.com/thing:4768343
which shares common mechanism for the reduction gear set.

Update Feb 24, 2021

Arduino code for stepper motor control is improved. Rotation is a bit smoother than before, with 8-phase control.

Previous sequence of coil voltage is as follows (4 phase control).

1 1 0 0

0 1 1 0

0 0 1 1

1 0 0 1

Current code is improved with the following 8-phase sequence.

1 1 0 0

0 1 0 0

0 1 1 0

0 0 1 0

0 0 1 1

0 0 0 1

1 0 0 1

1 0 0 0

Troubleshooting:

From the comments to this thing, I noticed there are some different versions in the market. Some motor runs to the opposite direction.

If your motor runs to the wrong direction or generates noise with weak torque, please change the order of the numbers in code as

int port[4] = {4, 5, 6, 7};

to

int port[4] = {7, 6, 5, 4};

where the numbers are related to the pins of Arduino nano (D4 - D7).

If the motor does not run smoothly, or generates noise with weak torque, change the order to find better one. Stepper motor never breaks by changing orders.

Since a stepper motor consumes a lot of power, Arduino become unstable with low-voltage USB power source. To solve the problem, try to do the followings:

• Jump (short) the diode under the USB connector of Arduino nano (as left picture above).
• Add a capacitor between 5V and GND (as right picture above). I used 10uF capacitor.

or

• Use an independent 5V power source to the stepper motor amp.

For the details of assembly, wiring and coding, please take a look at related thing, https://www.thingiverse.com/thing:4768343

and https://www.thingiverse.com/thing:4761858

Category: Gadgets