Introduction: Apparition Apparatus (Halloween Prank)

About: I work at RobotZone ( the folks behind Actobotics and ) in Winfield, KS. I love working on projects with my kids and seeing what they create.

So I decided to create a Halloween themed prank where a pencil cup mysteriously moves by itself or even flies off of a table next to an unsuspecting co-worker. Muwuahahahahaha!

Step 1: What You'll Need

Full Parts List:
58544213.00" Aluminum Channel
585494190° Hub Mount Bracket A
6382581624 RPM Precision Planetary Gear Motor
5551721Planetary Gearmotor Mount A
62511814mm to 1/4” Shaft Coupler
63405811" Precision D-Shaft
54554811/4" Set Screw Hubs
6051181Input Power Board
54562021" Bore Tube Clamp D
63215841" Diameter Magnets (South) (your mileage may vary.. you may need more or less depending on the thickness of the table/desk you are going through)
63216041" Diameter Magnets (North)
5More 1" Diameter Magnets for the bottom of the pencil cup (Polarity does not matter as long as you face them all the same direction)
5854821Channel Bracket B
6050511SPST Push Button Switch
1MB1040 Ultrasonic Rangefinder + 7 pin right angle header row
HC-SR04 Distance Transducer Sensor
561-KSP22#4 Nylon Spacer (0.125") (for mounting sensor)
91251A10824-40x3/8" Socket Head Machine Screws (for mounting the sensor)
90480A00524-40 Machine Screw Hex Nuts
501Arduino Uno
5850081Arduino Channel Snap Mount
6051361Small Solderless Breadboard
5850601Breadboard Snap Mount
54537211/8" Hub Spacer (spaces up Breadboard Snap Mount)
75511N4001 Diode
9761TIP120 Power Darlington Transistors
74411k Ohm resistor
various jumper wires
ZC.1000.3S.2513S LiPo battery
42 small screws to mount the 90° Hub Mount Bracket to the underside of the tabletop. And one or two small screws to mount the Channel Bracket B (with all the electronics) to the table/workbench as well.
2depending on how you space your magnets you might neet a couple of small washers between the 90° Hub Mount Bracket and the underside of the tabletop
63210885/16" Socket Head Machine Screw (for mounting the 1" Bore Tube Clamp which hold the magnets)
63211083/8" Socket Head Machine Screw (for the hub and motor mounts)


Step 2: The Brawn: Assemble the Magnet Tornado

  1. Solder the Input Power Board to the motor (optional... makes it easy to connect to the motor with just jumper wires or a JST connector)

  2. Use a small phillips screwdriver to attach the motor mount to the motor.

  3. Screw the motor mount to the 90° Hub Mount Bracket

  4. Put the 1" D-Shaft into the Coupler and then put the coupler onto the motor shaft and tighten both set screws well (tighten the set screws with a 3/32” Hex Key.

  5. Mount the Hub to the bottom middle of the 3" channel

  6. Insert the D-Shaft into the Hub and tighten the set screw.

  7. Mount 4 magnets into one of the 1" tube clamps and 4 in the other.

  8. CAREFULLY attach the magnet/clamp assemblies into the ends of the channel... make north facing out on one side and south facing out on the other.


Each of these magnets has a Gauss Rating of over 13,200! Putting them in groups of 6 makes them SILLY STRONG --- THEY CAN AND WILL MESS UP YOUR DAY IF YOU ARE NOT EXTREMELY CAREFUL.

Also... don't set them next to your phone.

Also trying to assemble anything affected by magnets within a nearby proximity will quickly make you look like you are both drunk and riding a roller coaster will performing the task.... you've been warned!

Step 3: The Brains: Assemble the Ever Watching Eye

I used a MB1040 Ultrasonic Rangefinder because that is what I found lying around... this is about $30 but since we are not doing anything real precise a cheap facsimile should do nicely (for example a HC-SR04).

I soldered a 7 pin male header row to the MB1040 and bent it 90° (though if you are buying new header rows you can buy a pre-bent "right angle" header row.)

Since I am not a huge fan of crimp terminals so I soldered two female jumper wires to my push button and shrink-wrapped it up.

Go ahead and mount the breadboard mount, arduino channel snap mount, button and sensor as shown.

Step 4: The Brains: Wiring It Up

I started with my simple cheap motor controller and hooked up the power to the sensor and the pwm pin on the sensor to pin8 on the arduino. I also added a SPST push button so that I could easily turn the project on and off.

Step 5: The Brains: Programming the Arduino

You'll need the Maxbotix library from

Step 6: Final Prep

Now Mount the brains and the brawn to the bottom of a workbench or table. I was fortunate enough to have the perfect workbench, with some convenient 2x4s to mount the brains to. Mounting the brains far enough back made it completely hidden to anyone taller than a child.

Prep the Cup:
Put 5 or so magnets on the bottom of the metal pencil cup... make sure they are all facing the same direction.


Next do some tests to figure out the best place to set the pencil cup. I marked my favorite spot with a light pencil line.

Step 7: Go Time

Once the trap was tested and armed I set a piece of paper next to pencil cup... I then asked co-workers if they could give me some feedback on a project idea that I had put together.