I've always been facinated by the "Overbalanced Wheel", which is basically a wheel with weights that slide or move from a position close to the center of the wheel to a postion near the edge of the wheel as it turns; basiclaly shifting more weight to one side of the wheel to keep it turning in that direction.
I decided to build my "Overbalanced Wheel" out of an old CD (always great for DIY projects), some screws and metal brackets I bought at Lowe's and a few "secret" components that will be revealed in Step 5.
NOTE: Don't look ahead to Step 5 unless you want to take the fun out of perpetual motion!
First, check out the video!
Step 1: Materials & Tools (Non-Secret)
Non-Secret Materials Needed:1 - CD
8 - 6-32 Cap Nuts
8 - 6-32 Screws
8 - 6-32 Washers
8 - 6-32 Nuts
6 - 1/2" x 4.5" x .035" Metal Mending Plate (Lowes 364404)
4 - 1/2" x 1-1/2" x 1-1/2" Metal 90D Plate (Lowes 364311)
1 - 1/2" x 3" x .035" Metal Mending Plate (Lowes 364323)
1 - 2" Metal Gear Shaft
1 - 1" Diameter plastic gear (to fit shaft above)
2 - Rubber grommets (same diameter as gear shaft)
Non-Secret Tools Needed:Drill
Hot Glue Gun
Step 2: Designing and Building the Wheel
My Wheel DesignI decided to cut slots in the CD and use weights made of screws, nuts, and metal caps to slide back and forth in the slots. I figured the slots needed to be angled from the center of the CD out toward the edges so the weights would slide "out" as each slot reached the falling edge and slide "in" as each slot reached the rising edge of the CD when turning clockwise.
STEP 1: Lay out the design on paper by dividing the CD into eight equal sections.
STEP 2: Add a 1/8" hole 1/4" from the edge of the CD for each dividing line.
STEP 3: Measure half the distance between each hole and the center of the CD and add another 1/8" hole for each dividing line.
STEP 4: Join the holes to make a 1/8" slot for each hole pair. (See the first photo).
STEP 5: Cut out and tape the pattern to a CD. See my note at the end about protecting the CD while drilling and cutting.
STEP 6: Drill the holes first being careful not to crack the CD.
STEP 7: Use a Cutout Tool with a 1/8" cutting bit to make the slots between each set of holes. Make sure you securely brace the CD and cut in a slow, smooth motion. Otherwise, you will likely crack the CD.
STEP 8: Clean up the slots using a Dremel. The weights must slide freely, so be sure to remove any burs or narrow areas in the slots.
STEP 9: Hot glue the plastic gear to the back side (label side) of the CD making sure to center it. I added a piece of silver tape under the gear to hide the gear teeth from the front of the CD. Some CD labels cover this area so the tape won't be needed.
STEP 9: Insert screws, washers, and cap nuts through the slots. The cap nuts should face the front (shiny side) of the CD.
NOTE: As you can see from the photos, I scratched up the surface of the CD quite a bit during the building process. In retrospect, I should have protected it better during drilling, cutting, and sanding.
Step 3: Building the Frame
I built a simple triangle frame using hobby metal from Lowes.
STEP 1: Assemble a triangle using three 4-1/2" flat plates and two 90 degree plates leaving the top screw & nut out.
STEP 2: Assemble a second triangle as shown in figure 2.
STEP 3: Add a 3" flat plate to the back of the frame to stablize it.
STEP 4: Insert the wheel by sliding the the gear shaft through the top holes in the frame.
STEP 5: Add 90 degree plates to each side (3rd hole up) to further stablize the frame.
STEP 6: Insert grommets on each side of the grear shaft to keep the CD centered in the frame
Step 4: Testing It Out
Since we've already established that perpetual motion is impossible, I didn't expect this to work. However, I had no idea it would fail so miserably! Fact is, IT DOESN'T WORK AT ALL! It doesn't even start to work when I give it a nudge. If I spin it fast, it will run about as long as a wheel with no weights at all; maybe not even as long as that.
Now that that's over, please move on to Step 5 where the real motion begins...
Step 5: The Real Deal (Non-Perpetual Motion)
SPOILER ALERT - If you haven't gone through steps 1-3 or you want to keep believing in perpetual motion, please don't read this step.
Okay, so perpetual motion failed miserably. Now it's time to add some real motion to the project! I wanted to hide all of the electronics behind the CD (and remember the CD has slots cut in it), so everything had to be small; very small!
My first thought was to use a simple DC motor with a battery and a switch. But there is no good way (that I could figure out) to make it turn slow enough (and with enough torque) to resemble perpetual motion. I tried a potentiometer, gears, and PWM. Nothing worked to my satisfaction.
So I decided a servo and microprocessor were needed, but they had to be very SMALL. The smallest servo motor I could find was the HD-1440A from Pololu . This is a great little servo with plenty of torque.
Next, I needed a really small microprocessor to handle the PWM to drive the servo at the desired speed. For this, I used a Teensy 3.0. Luckily, I happened to have a Teensy on hand since I was a contributor to their successful KickStarter campaign. The Teensy was perfect for this project; very small and easy to program (Arduino compatible). Plus, as a bonus, the Teensy has a special feature called "Touch Sense" that let me start and stop the wheel by simply touching the frame. This way I could give the illusion of starting the wheel by giving it a nudge!
Secret Materials Needed:1 - Teensy 3.0 Microprocessor
1 - Teensy Arduino IDE
1 - Mini servo (HD-1440A)
1 - USB connection to a computer
1 - Small plastic driver gear
1 - 1/2" x 2" x .5" Metal Slotted Angle (Lowes 364266)
Secret Tools Needed:Solering Iron
Step 6: Preparing the Servo Motor
As with most servo motors, this one was configured for 180 degree motion. I needed continous rotation to turn the wheel, so I hacked it as follows:
STEP 1: Remove the two small screws from the bottom of the case.
STEP 2: Cut the label along the seam near the bottom of the case and gently pull the bottom cover loose.
STEP 3: There are three wires that connect the circuit board to the potentiometer. Detach those wires from the POT.
STEP 4: Since we only need the wheel to turn in one direction, you can just solder a 2k (approx) resistor between the two wires indicated in the photo. I had to experiment a bit to figure out which two wires needed to be connected to give a clockwise rotation.
STEP 5: Cut the access leads and cover the resistor with electrical tape (or shrink wrap) and carefully put everything back in the case.
STEP 6: Hot glue the plastic drive gear on top of the very small gear of the servo. Be sure to center this gear. I used a small nail in the center to line them up while glueing.
Step 7: Programming the Teensy
Before programming the Teensy, you'll want to download the Teensy Loader and Teensyduino add-on for the Arduino IDE. After that, copy this simple sketch, compile, and load your Teensy. Notice the "touchRead" command that senses touch by reading capacitance. More info is available here: http://www.kickstarter.com/projects/paulstoffregen/teensy-30-32-bit-arm-cortex-m4-usable-in-arduino-a/posts (search for Touch Sensing).
// Overbalanced Wheel
// Using Teensy 3.0
// by Mike Soniat
int servoSpeed = 170;
int servoPin = 14;
int touchPin = 22;
int touchReading = 0;
boolean isStarted = false;
touchReading = touchRead(touchPin);
if (touchReading > 3000)
isStarted = !isStarted;
Step 8: Connecting the Servo to the Teensy
STEP 1: Cut the connector off the servo wires and solder the wires to the Teensy board as follows:
- Brown (-) wire: Solder to any GND pin. I used the one at the bottom center of the board.
- Red (+) wire: Solder to either of the 3.3V pins. I used the one next to the GND pin at the bottom of the board.
- Gold (signal) wire: Solder to any "PWM" or analog pin. I used pin 14.
STEP 2: Solder a length of wire to any "Touch Sense" pin. I used pin 22.
Step 9: Putting It All Together
STEP 1: Place a piece of double-sided tape on one side of the servo and attach it to the angle bracket.
STEP 2: Attach the angle bracket to the back of the frame as shown and adjust the postion of the servo gear to mesh with the CD gear.
STEP 3: Place another piece of double-sided tape on the back of the Teensy board and attach it to the back of the frame as shown.
STEP 4: Run the "Touch Sense" wire around the top of the board and attach it to the frame as shown.
STEP 5: To hide the USB power lead from sight during operation, cut a slot in a box or other base and run the USB cable up through the slot to the Teensy board. Tie wrap the cable to the frame if needed.
STEP 6: Turn the base around and you're ready to amaze your friends (as long as you keep them a few feet in front of it)!
Here's the video again in case you missed it in the Intro: