Hollow Clock 4

June 3rd, 2024: The New Hollow Clock V is released!

New version of the Hollow Clock is released. Contrary to the former version (Hollow Clock 3), the angle of the hour hand is controlled not mechanically but magnetically. Very easy to adjust the time.

• Three 8mm x 3mm neodymium (neodym) magnets
• 28BYJ-48 stepper motor and its driver board
• Arduino nano
• 2mm tapping screws (short : 5, long : 1)

• Print all parts with supplied posture. No support needed.
• Select either "case-side-hole.stl" or "case-rear-hole.stl". The former one is intended to enclose the all of the circuits including Arduino nano and driver board. Please use the latter one if you want to use the other types of micro controllers outside of the clock base.
• "washer1.stl" and "washer2.stl" are the optional parts to adjust the clearance of the gears.
• Wooden version (shown above) is made with CNC milling machine.

Since the room for the circuitry in the bottom case is very limited, it is somewhat tricky to enclose them in the case.

• Bend and cut the pins of the driver board as shown above.
• Solder the Arduino nano inclined.
• Test your circuit with the test code, "stepper-test.ino" for Arduino IDE.

If you want to use the other micro controllers, please use "case-rear-hole.stl" for the bottom case. In this case, the control circuit should be placed outside of the bottom case.

• Remove debris and blobs from the parts well for smooth rotation.
• Please make sure that all axes rotate smoothly before assembly.
• If the engagement of the bevel gears are too loose, use "washer1.stl" and "washer2.stl" to tighten the clearance.

• Remove debris and blobs from the parts well for smooth rotation.
• Stack the all rotors.
• Attach the hour hand to the minute hand with a screw of certain length.
• Insert the magnets and test how it is aligned by the attractive force.
• Please make sure that all axes rotate smoothly before assembly.

• Insert the display unit to the driver unit and check it rotates nicely.
• Flush the clock code, "hollow4.ino".

If "hollow4.ino" does not work well, try to use "hollow-8phase.ino". The sequence of driving the stepper motor is different. Which is better for your clock depends on the friction of your clock .

• "hour-hand-5mm-shorter.stl" has been added for better visibility (to distinguish two hands). The attractive force is relatively weak but still works in my case. Please try it!
• I painted the frontal surface of minute hand. If you do not want to use paint, print "colored-plate-for-minute.hand.stl" with the other material and stick it.
• "min-rotor-thick-hand.stl" has a bit thicker minute hand. If you can change the material during the print (using "pause-at-height" function of the slicer), use this model to give different color the hand.

Troubleshooting:

• If the engagement of the two bevel gears are too loose, use washer1.stl and washer2.stl to tighten the clearance.
• If the square shaft of the worm gear is too loose with the square hole of the bevel gear, please use bevel-gear-small-hole.stl. (zero clearance version)
• From the comments to this thing, I noticed there are some different versions of the stepper motors 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] = {5, 4, 3, 2};

to

int port[4] = {2, 3, 4, 5};

where the numbers are related to the pins of Arduino nano (D2 - D5).

• 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.
• If your clock is not stable, check the quality of the power source (USB wall adapter).
• If your clock runs too fast or slow, please adjust the value named MILLIS_PER_MIN at line 3. Thoretically it should be 60000. Smaller number means fast rotation.