Fig. A: Regular old optomechanical mouse guts.
Fig. B: The rotary encoder disk mated to a motor.
Fig. C: The battery, switch, and motor circuit. Why buy
a battery box when you’ve got electrician’s tape?
Fig. D: Everything in its place, ready to spin the cursor
to the left-hand side.
the shafts of a pair of rotary encoders (disks with
notches cut into their edges). Spinning an encoder
breaks an IR beam, which drives cursor movement.
Joe had attached a DC motor to the x-axis encoder
disk (hence the noise). My confused computer
thought someone was sprinting the mouse down an
infinitely long table. My attempts to budge the cursor
were overwhelmed by this much-harder-working
prank mouse. I’m honored to have been so cleverly
pin, making a starter hole. Then I heated the metal
motor shaft with a lighter until it glowed red, and
pressed it into the plastic shaft.
4. I wired my motor to a switch and AAA battery. You
could add a variable resistor to adjust cursor speed;
a slow drift would be really evil. Joe was pressed for
time (he built this prank during lunch, the fiend!) so
he seems to have used glittery hot glue for all the
fabrication. You should solder and heat-shrink your
connections to avoid shorting things out.
How It’s Done
1. Get an old mouse that uses a ball, rather than an
optical sensor. Peel any stickers off the mouse’s
underbelly, looking for screws. Remove these and
pry the mouse open. Remove the ball and save it
in your jar of spherical things.
5. Snap the encoder in place, then mount the motor to
the mouse housing. Taking a cue from Joe, I resorted
to hot glue, too.
2. Pull a DC motor from an old toothbrush or toy
helicopter. Based on the size of your motor, measure where to cut the x-axis encoder shaft, then
carefully remove the encoder.
6. Switch on the motor and plug the mouse into
your victim’s computer when they aren’t looking.
Listen for the screams of cursorial frustration to
ring through the halls.
Please send any counter-prank ideas my way.
3. Cut the excess shaft off with a knife. Here’s the
tricky part — mating the encoder shaft to the motor
shaft. I “drilled” into the plastic shaft end with a
John Edgar Park ( firstname.lastname@example.org) is a character mechanic
at Walt Disney Animation Studios and host of the
upcoming PBS television series, Make:TV.
Photography by John Edgar Park
150 Make: Volume 15