Introduction: Gravity Light

I designed this gravity light using a motor from an old microwave oven.
This light will provide enough light to read with for about 5 to 10 minutes depending on the height that the generator is mounted above the floor, the weight used and the individual characteristics of the motor.

An estimated 16 percent of the world's population — 1.2 billion people — have little or no access to electricity:

This is designed as a school project, the skills/knowledge to be gained include:

3D printing





Tying knots (fishing & others)

Social Science & 3rd world awareness


Performance varies depending on many things, so using the best of 5 motors that I had tested I measured the performance - using an LX Meter App on my phone, and with the reflector 12 inches (300mm) above the meter and the generator 10ft (3m) above the ground:

Weight - - - LX - - - Time

= = = = = = = = = = = = =

1kg - - - - - 32 - - - - 8:10

1.15kg - - - 45 - - - - 7:45

1.3kg - - - - 62 - - - - 7:00

As you will see in one of the photos, to get the weight of 1.3kg I used a 1 litre water bottle and the 2 magnets from a microwave oven. What I found was that each motor needs a different weight to get to the point where the LX level suddenly increases.

The most efficient motor that I found was the Galanz GAL-5-240-TD.

Step 2: The Build:

The parts to be printed on a 3D printer can be found at:


1 x turntable (tray) motor either from an old microwave oven OR from the internet (220-240V 4W Synchronous Motor) I have not tried a 110V motor yet. The photos attached show 2 different brands of motor that work and a different brand that does not work.

4 x Silicon diodes (e.g. 1N4148)

2 x 1000uF 63V Electrolytic Capacitors OR 1 x 2200uF 63V

Figure 8 speaker cable OR similar

Braided fishing line for pulley

Thin twine for harness for the water bottle weight using the 2 rings that you print out Thin twine OR curtain nylon cord to tie frame to the wall

2 x M3 25mm screws

4 x M3 12 mm screws

2 x M3 nuts M3 washers (optional)

4 small self tappers OR similar to hold the LED in place

1 x small metal (key) ring (optional to join weight to fishing line)

1 x 2 litre (0.5 gallon) plastic container to hold water

1 x LED (50W 12V-36V High Power LED Lamp Light COB SMD Bulb Chip). See photos for LED style.

1 x Curtain OR roller blind chain, the length to suit mounting height (looped is tidier, but slightly more expensive), suggest at least a 1m loop (2m total length) with a ball size of 4.5mm

Aluminium foil (cooking from your kitchen)


3D printer

Soldering iron

Various hand tools Light meter OR an App on a Smart Phone (e.g: “Physics Toolbox Sensor Suite”)


Do not pull the left hand side of the curtain chain, as the Tension Post may break.

The assembly needs to be mounted to a wall or other vertical surface, not a horizontal surface.

The LED can be hung from an appropriate point or print the 3D brackets and make a table lamp.

Where the screws are going into the plastic without a nut, they will tap into the PLA plastic to make their own thread, so if the plastic used is very hard it may be best to file a slight point onto the screw tip, or using a Phillips head screwdriver slightly countersink each hole.

Knots: Reef Knot – for the water bottle harness.

Uni Knot - on each end of the braided fishing line.

Figure 8 – for each end of the cord holding the frame to the wall.

Step 3: Kits:

My son is keen to make some pocket money, so he is going to provide kits for those that are interested, all you will need is a 3D printer, PLA filament, some aluminum foil from your kitchen, and a suitable (milk/water) container for the weight. The kit will probably cost about $AUS30 to $AUS40 ($US25 to $US35) per kit including shipping. Please let me know if you would like to be notified when they are available.


I will write these up over the next few weeks if there is enough interest.


I would be really interested in any enhancements that you make or suggestions that you have.

A challenge is to build a gear box to double the revolutions of the generator in order to either double the duration or double the light intensity depending on whether or not you double the weight.

A very subtle refinements could be to replace the silicon diodes (junction voltage of say 0.6v) with Schottky diodes (junction voltage of say 0.3v) or fast switching diodes, but I don't expect it to make any visible difference.

Step 6: Questions and Activities:


How do generators work?

Are there differences between electric motors and generators? Explain.


What is the difference between AC and DC voltages?

What are LED's?

The LED is polarised, what does this mean?

Describe how to convert AC to DC. OR explain how a half wave and full wave rectifiers work.

What is the capacitor(s) used for?


What units are used to measure light?

To undertake some or all of the following it is good to have a light level meter (see tools above) so that you can test the different light levels at a consistent distance from the


without the reflector installed and with 1 diode and no capacitors (also notice the flickering) with full bridge rectifier and no capacitors with full bridge rectifier and 1 capacitors with full bridge rectifier and 2 capacitors with the reflector installed, but no aluminium foil with the reflector installed and aluminium foil


Why use fishing line rather than something thicker? (You could try using a thicker line)

What are the advantages and disadvantages of using a large gear radius?


Why is the front of the frame not perpendicular? (You could try inserting a wedge between the top of the frame and the wall to see what happens).

On the frame, why is the junction between the top and front braced, but the middle stand-offs and bottom are not braced?


What is solder made of ? And why.

What temperature does typical solder melt at?

THIRD WORLD CHALLENGES: Using the internet, find out what percentage of the world's population don't have electricity? Then watch the TED talk:

Either summarise the TED talk, OR use what you learnt in a short
story (fiction) adapted from this talk (e.g. create characters with names and a little story about them).

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