Mechanical 7-segment digital clock

Mechanical 7-segment digital clock with 23 segments, controlled by only one RC servo motor. Not only all segments but also carries between digits are mechanically resolved.

• display size (size of the front panel) : 23cm x 10cm
• digit size : 8 x 4cm (the area of center line of each digit)

It consists of 54 types, 115 parts printable with common 3D printers. You also need

• 1 RC servo motor (normal, full size servo. I used Sanwa SRM-102Z)
• 1 micro:bit and 5V power supply (break-out board, etc.)
• 7 rubber bands
• 19 M3 bolts
• paint (ex. white paint for black 3D printer material)

Necessary tools

• sand paper or file for deburring
• soldering iron for welding plastic
• M3 Screw tap (if you do not use tapping screw)
• Silicone grease or spray for lubrication

Tips

• all parts can be printed out without supports.
• for smooth operation, deburring and lubrication is very important.
• A few cases of breaking rothook.stl (ratchet hook) during the daily use are reported. To solve this problem, print the rothook.stl with a bit larger scale (ex. 103%). It will also solve the problem of very heavy load and loud noise of ratchet.

Update 2020/12/6

• Single digit unit is released. It is easier to make and good for a trial. The video of that one includes a guide of assembly, so please check it out.

https://www.thingiverse.com/thing:4676614

Update 2021/10/31

• Improved single digit unit is released. Number of the parts is much reduced. It does not use rubber bands and requires very small force to drive.

https://www.thingiverse.com/thing:5066794

Note

This 7-segment cam mechanism is invented by Peter Lehnér, https://t.co/R4ZO4ZHFVy https://www.thingiverse.com/thing:3351710

Custom Section

I recommend plastic welding using soldering iron, because it is fast and secure. It is also possible to disassemble by melting the weld part.