This is useless machine ready for Halloween party. Traditionally useless machine are stubborn and persistent. This machine is the same, but it is more aggressive and tries to bite an intruder ( I warned you!).
Step 1: Circut Diagram
Its electrically design is very traditional. You can find a lot of such schematic online as well as "how it works" explanation. I put this diagram here just for reference. Here is list of components:
- Solarbotics GM2 gear motor
- Radioshack DPDT Rocker Switch ( 275-695 )
- Radioshack SPDT Switch with Roller Lever (275-017)
In addition you need four rechargeable AA batteries (any kind is fine), battery holder, some wire and (optional) wire connectors.
Step 2: Kinematic Scheme
Mechanically this machine is very different of what you usually find. Instead of toggle switch there is the rocker, it does not have an arm and box lid performs the task of back switching the power off. I made several paper simulators till found suitable mechanical proportion.
Step 3: Box Lid
As you can see from photos this machine is the result of trail and error process rather than proper mechanical design. I do not have drawing with precision dimensions. But I believe attached images are good enough to illustrate how it was built and how it works. Box lid is most complex component here. Pay an attention to the gap between lid and rear round stick. The gap should be wide enough to allow 2 mm of plywood fit in to it but not too wide. That gap allows sliding of the lid along box plywood strips.
Step 4: Box Sides, Motor and Slide Rails
Here is box walls with attached non-sliding portion of the lid with switch. Motor is mounted inside the box on the front wall. Here you can see motor lever as well. Pay an attention to wide plywood strip at he top. They serves as rails for lid to slide back and force.
Step 5: Box Base
Here you can see micro-switch mounted with holder on the box base. Its location should match movement of the lid lever, so at the bottom position of the lever switch is off. It should be not glued but mounted with small screw.
Step 6: Batteries, Screws
Four AA rechargeable batteries requires the batteries holder. At the side of the holder there are two two pieces of Velcro. Velcro allows easy attach holder to the box and detach it if there is time to recharge.
Two shorter screws used to tie base to sides, longer screw is to attach lid and motor levers.
Step 7: Assembling and Testing the Machine
After assembling the machine there is no guarantee that everything will work as expected. If micro switch is located too high, lid will not close fully. If it is too low, the motor will not stop on its way back. I used the next approach to overcome that problem. Initially micro switch was set a little bit low, to be sure that on the way back lid is closed. Than I detached batteries, unscrewed the base and micro-switch holder, added some paper pads between micro-switch holder and the base, assembled it again and tested. After couple of iteration it started to work as needed.
Step 8: Pumpkin Hallowen Mask
And the last thing is to make Halloween decor. Just in time I received order from Amazon with Kindle Fire Reader. It was packaged into orange envelop made out of thick paper: perfect material to make a mask. My art skills are very rudimentary, I am sure you will do better.
Step 9: Ready for the Party
Now the machine is ready. Whenever your guests will ask "Trick or Treat" give them the treat only after they push the box switch.
If you find useless machine concept interesting you may want to look into my other posts dedicated to that topic: