You've probably seen the Most Useless Machine before, but I thought it would be fun to build a temporary one with littleBits modules. For those of you who haven't seen it, this is the machine that does nothing except turn itself off as soon as you turn it on. littleBits provides all the electronics you need to build a Most Useless Machine, so I borrowed my nephew's Premium Kit, added the "Double OR" and toggle switch modules, and I was ready to go.
This Instructable is mostly about the electronics (there are plenty of write-ups on building the enclosure) so I'm just describing a basic setup here. You can add your own enclosure once you understand how this machine works.
The theory behind this setup is straightforward due to the functions of the littleBits modules.
- Power is split by the Branch module to both the toggle switch and the roller switch. At first, both switches are off.
- Then, both switches feed into the "Double OR" module. This means that if either switch is on, then power is supplied to the rest of the circuit.
- The servo motor is configured to swing, so when the toggle switch is turned on, the servo swings the shutoff arm to turn off the toggle switch.
- At the same time, the servo triggers the roller switch, so the servo continues to run. When the servo swings back to its original position, the roller switch is turned off, thus turning the entire machine off.
Step 1: Parts
- Power (any of the power modules will do)
- Roller Switch
- 2 Wires
- Servo Motor
- Double OR
- Toggle Switch
You also need:
- a wood base board
- a small block of wood to mount the servo motor
- a wire coat hanger
- a short length of a wood dowel
- a small rubber band
- a garbage bag tie (or any thin wire that can be used for fastening)
- cable ties
- a small wood screw
- screwdriver for the screw aove
- drill with small drill bits
- wire cutters
- needle-nose pliers
Step 2: Mount Components Onto the Board
Cut 2 pieces of coat hanger wire and create the following (look at the picture for guidance):
- An arm guide that is a double eyelet about 1.5" tall.
- A 5" shutoff arm that is basically a straight wire with a squared hook on one end.
Thread the shutoff arm through the arm guide's top eyelet, and attach the hook end to the servo motor's upper arm using a garbage bag tie.
At this point, the arm will be too long, so we need to adjust it. Rotate the servo arm extends farthest towards the toggle switch. Cut the shutoff arm about 1/8" short of the toggle switch in of f position. Cut a piece of wood dowel about 3/8" long. Drill a very shallow 5/64" hole in one end and plug the dowel onto the end of the shutoff arm. Bend the shutoff arm so that the dowel squarely hits the toggle switch. If the arm/dowel is too long, drill the dowel hole a little deeper and check again.
Double loop the rubber band and loop it around the roller switch. With the lower servo arm pointing closest to the roller switch, attach the rubber band to it using a garbage bag tie. Tie it so there's no slack in the rubber band, but be sure the switch is not triggered in that position.
Step 3: Attach the Remaining LittleBits Modules
Look at the attached picture and annotations to see where the remaining parts go.
Step 4: Adjust the Shutoff Components
Turn on the power switch and then flip the toggle switch to give your Most Useless Machine a whirl. If the shutoff arm misses, then congratulations, you have a truly useless Most Useless Machine. Bend the shutoff arm or adjust the dowel to make sure the toggle switch is hit when the machine is turned on. Adjust the rubber band to make sure that it triggers the roller switch when the servo first runs, and it turns off when the servo motor returns to its original position.