Useless Machine

Author: pcdangio, published on 2014-12-23

Click this button to get the 3D model


This is a 3D-Printable “Useless Machine”. Hit the switch, and the useless machine uses a tiny arm to switch itself back off. These are popular gag gifts, and make for a great desk toy!

You can print this one yourself, and the parts are really cheap. Check out the instructions for a parts list and assembly steps.


Parts List:


1x Micro Gearmotor


1x DPDT Toggle Switch
1x SPDT Limit Switch
2x 1-AA Battery Box


1x M2.5 Metric Tap
1x M3 Metric Tap
1x Tap T-Handle
10x M2.5x10mm Machine Screw
6x M2.5x8mm Machine Screw
1x M2.5x5mm Machine Screw
2x M3x14mm Machine Screw

Misc Parts

24AWG Wire
Soldering Equipment
Metric Hex Wrenches/Allen Keys

Assembly Instructions:

NOTE: There are two images in the gallery to help with assembly. One is for the electrical schematic, the other is to show how parts are oriented inside of the shell.

  1. Use a knife to cut the mouse ears off of the base, top, shell, and hatch. Use some high-grit sand paper to smooth out the cuts.
  2. Tap all of the 3D printed parts using the M2.5mm Tap. The shell has through holes all the way through, but you only need to tap about 8mm down on each side. DO NOT tap the holes in the top plate that will be used to attach the hatch.
  3. Tap the SPDT lever switch holes using the M3mm tap.
  4. Solder the components using the schematic shown in the picture gallery.
  5. Attach the motor to the base plate using the motor bracket and 4 of the M2.5x8mm screws. The side of the motor with the electrical terminals should be on the same side of the base plate as the slot. The shaft should be pointing inwards on the base plate. Don’t tighten it too much or it will restrict the motor from turning.
  6. Attach the arm to the motor shaft. Use the M2.5x5mm screw as a set screw to attach the arm to the D-type shaft of the motor.
  7. Attach the SPDT Lever Switch to the Kill Switch Mount.
  8. Attach the Kill Switch Mount to the base plate slot using 2 of the M2.5x8mm screws. Adjust the position of the mount in the slot so that the motor turns off when the arm is just about to touch the base plate.
  9. Attach the shell to the base plate using 4 of the M2.5x10mm screws.
  10. Attach the hatch to the top plate using 2 of the M2.5x10mm screws. Remember, these two holes should not be tapped. This allows you to tighten the screws into the holes without having to have the screw head be flush against the inside of the hatch. The idea is that the screws should be held tight by their threads, allowing the hatch to move freely. You may need to do a little sanding on the edges of the hatch to get it to move freely and rest flush on the top plate.
  11. Attach the DPDT Toggle Switch to the top plate. Remove the washers that the switch comes with; you only need the one nut to fasten the switch to the top plate. Make sure you orient the switch in the correct direction.
  12. Attach the top plate to the shell to complete the assembly. Obviously make sure you put some AA batteries in the battery box and place the box inside of the shell beforehand.

License: Creative Commons – Attribution – Share Alike

Tags: desk_toy, diy, funny, pololu, Useless_Machine