Shaky Leg Power Generator




About: My name is Randy and I am a Community Manager in these here parts. In a previous life I had founded and run the Instructables Design Studio (RIP) @ Autodesk's Pier 9 Technology Center. I'm also the author ...

Anyone who has spent any length of time near me knows that my leg shakes. Friends and family typically start to notice when the dining table starts to shake. What tips off coworkers is usually a shaking monitor and a subtle ripple breaking the surface tension of their coffee. After a while they realize it is not a mild earthquake, it is just me.

Most people can politely put up with it for so long. After a while even the most mild-mannered person will turn to me and say "Randy. Stop it!" I sympathize with them and do my best to keep my heel flat on the floor. It takes a lot of willpower to stay grounded. If my mind is left to wander, my leg starts to chase after it.

I'm not sure if at this point I will ever get to a place where my leg will ever stop shaking, but I can at least make the most out of it. Rather than radiate nervous energy pointlessly out into the aether, I have made this device to harness my involuntary leg-shaking and convert it into useful energy. From now on I can harness my anxious disposition to provide safe and clean energy to recharge all of the USB devices in our lives. Since I am now providing a useful service it is my hope that people will be less annoyed when I start to shake - or so one can dream.

Step 1: Go Get Stuff

You will need:

(x1) Expression pedal (RadioShack #55071404 - online only)
(x1) 3D printer (RadioShack #277-224)
(x1) Stepper motor (RadioShack #273-767)
(x1) PC Board (RadioShack #276-150)
(x1) LM7805 voltage regulator (RadioShack #276-1770)
(x1) 1000uF capacitor (RadioShack #272-1032)
(x1) 10uF capacitor (RadioShack #272-1025)
(x1) 0.1uF capacitor (RadioShack #272-135)
(x8) 1N4007 diodes (RadioShack #276-1653)
(x2) 15K resistors (RadioShack #55049437 - online only)
(x1) USB-A to USB-B extension cable (RadioShack #26-1709)
(x7) 1/2" spacers
(x7) 3/4" metal screws
(x1) M4 x 8mm nut and bolt
(x4) M4 x 12mm nut and bolt
(x4) 1/4" plastic spacers
(x4) M3 x 12mm nut and bolt
(x1) 3/4 diameter x 0.062 gauge wire compression spring
(x1) Acrylic disc (cut using attached template)
(x1) Felt disc (cut using attached template)
(x1) Hot glue gun

Step 2: Open the Pedal

Remove the screws from the underside of the expression pedal and open the case.

Step 3: Remove the Lever

Pull the existing lever arm off of the potentiometer shaft on the inside of the pedal.

Step 4: Remove the Circuit

Remove both of the potentiometers from the inside of the pedal.

Trim away all of the wires attached to the small circuit board on the base plate.

All of the initial circuit should now be cut free.

Step 5: 3D Print

3D print the motor mounting bracket and lever arm using the attached 3D models.

Step 6: Fasten the Motor

Attach the Motor to the motor bracket using 12mm nuts and bolts.

Step 7: Place the Motor

Position the shaft of the motor on the inside of the pedal where the potentiometer with the lever arm was previously situated.

Step 8: Drill

Using the bracket's mounting holes as guides, drill two 3/16 holes in the body of the pedal.

Be careful not to drill all the way through into the foot pad.

Step 9: Mount

Affix the motor mount to the body of the pedal using 12mm nuts and bolts.

Step 10: Attach the Lever

Slide the new lever arm onto the motor shaft such that the plastic pin attached to the top of the pedal is centered in the lever's channel.

Step 11: Power Circuit

Build the power regulation circuit as specified in the schematic.

Basically, there are are two bridge rectifiers - one for each coil of the motor. The 1000uF capacitor is used to store and filter the electricity generated to create a smooth signal which is then converted to a steady 5V by the LM7805 voltage regulator. The 10uF and 0.1uF capacitors are additional power filtering at the regulator stage.

The two resistors are required for pulling the data and clock lines low while charging USB2 devices. Without these, your device probably will not charge.

Step 12: Cut the Cable

Cut the USB cable in half and expose all of the cable's four wires.

Step 13: Attach

Attach the USB cable to the circuit board as specified in the schematic.

Step 14: Spring

Drill a 3/16" hole in the center of the plastic contact pad on the body of the expression pedal. Mount the acrylic disc to the top of this pad using a 8mm nut and bolt.

Glue the felt disc to the felt pad that is directly opposite the plastic contact pad.

Once the glue is dry, place each end of the spring around each of these discs to hold the spring in place.

Step 15: Attach the Motor

Solder the motor wires to the circuit board as specified in the schematic.

Step 16: Drill

Place the circuit board centered atop the pedal's base plate on the side opposite from the existing small circuit board.

Make marks for each corner mounting hole and then drill them using a 1/8" drill bit.

Step 17: Mount the PCB

Mount the circuit board to the base plate using 1/4" spacers and M3 x 12mm nuts and bolts.

Hot glue the USB cable to the base plate to keep the wires from snapping off the circuit board.

Step 18: Case Closed

Close the case up using 1/2" metal spacers and 3/4" screws.

Step 19: Use It

Plug in all of your devices and get charging. Don't expect a rapid charge from this device, but a slow steady trickle over the course of an anxious day.



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    68 Discussions


    Question 1 year ago

    Is there a way to use the foot pedal from the old guitar hero games I prefer to reuse old tech before I buy new.

    1 answer

    Answer 1 year ago

    If the guitar hero pedal has a potentiometer inside, it can likely be modified in a similar. If it has a push switch, it would be much more difficult because there might not be enough travel.


    2 years ago

    umm where do i get a 3d printer? ): i wanna make it ];


    2 years ago

    I am not sure. It would depend what the mechanism and space inside the sustain foot pedal looked like.


    3 years ago

    hm i am not a shaky leg kinda person... but some of my classmates are.... their (bad) habit can finally put in good use!!


    3 years ago on Introduction

    Can any1 tell me the approx cost of this project ? plz mail me on


    4 years ago on Introduction

    Great device. Would like to see a non-3d printer version. Also, check this out for info on restless leg syndrome:

    2 replies

    4 years ago on Introduction

    Great Idea! I have driven people nuts with my leg shaking. I wish I had thought of it.


    4 years ago on Introduction

    Am trying this for the first time and have been able to get a hold of all the components. The issue is I don't know how to solder the components that well and moreover, the idea behind the 0.1 uF and 10 uF capacitors confuse me. The picture shows there is a 1 uF capacitor, so I'd like to know if fixing one 1 uF capacitor is sufficient for the circuit?


    4 years ago on Step 19

    Randofo, if you want, use a USB powerbank connected to the output, and you have a "Shaky-foot"-charged USB battery.


    4 years ago on Introduction

    I am making this for my 8th grade science fair, except i am hooking up a bike instead of a expression pedal. Also this my first complex electrical project, how did you connect the diodes, capitators, etc. to the wires?


    4 years ago on Introduction

    Is there any way that this could be made by using a bicycle dynamo instead of a stepper motor?

    It says you used a 1000uf capacitor but what voltage is it? Once its fully charged what do you say you get as a charge out of it(a few minutes with the LM7805 voltage drop) ??? Working on a project could really use a response quick. i am actually making a very similar project using electro magnetic coils rather than a motor. very similar setup and this is the fist time seeing your work. I enjoyed it.