# Kite With Wind-Powered LEDs

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## Introduction: Kite With Wind-Powered LEDs

I just finished making a device that lets a kite generate electricity and light up the sky at night.  The main goal for this project was to make something fun that can illustrate the power of the wind and help people make a tangible connection to wind power.   The kite has 4 small turbines that power two strips of RGB LEDs.  The LEDs are controlled by an IR remote and can flash or cycle through pre-set color sequences.

Here's what I used.
Materials
• 2-line stunt kite (Mine is the Nexus made by Prism)  A simple 1-line kite would potentially work too. Note:  After consulting some kite enthousiasts, it turns out that a stunt kite is not the best choice for carrying all the extra weight of the generators, etc. however it is handy for making cool patterns in the sky at night.
• 1/2" square Balsa wood beams (from a hobby shop)
• 8 1/4-20 set screws
• Hot Glue
• Heat-shrink tubing
• Solder
• 4 Radioshack Motors (I refer to these as motors or generators interchangeably)
• 3D Printed PLA
Tools
• 123D (free CAD software from Autodesk)
• Calipers
• 3D Printer (I used a Series1 made by Type A Machines)
• Soldering Iron
• Hot Glue Gun
• Wire Stripper
• Hex-Wrenches
• Sander
• Multimeter
• DC power Supply

## Step 1: How Much Power Is Up There?

When starting a project like this, I begin by asking myself "Is it possible?"  In this case, is the amount of energy I can harvest with a kite more than the amount of energy I need to light a string of LEDs?

I started by making a scale drawing of the kite and exploring different dimensions and layouts.  (This was before the kite arrived in the mail.)  I found that 7" propellers fit nicely with the layout I chose.

Next, I did a rough calculation of how much kinetic energy is in the air that passes through the 7" circle swept by one of the propellers.
• Start with the equation KE = .5 (Mass) * (Velocity).2  We will calculate the kinetic energy in the amount of air that passes by in 1 second.
• (Velocity) A strong kite-flying breeze is about 25 mph.  That's close to 10 meters per second.
• The Mass (per second)  is  (cross sectional Area ) * the Velocity * the Density of air.  (The density of air is about 1 kg/m3.)
• That means that KE = .5 * (cross sectional Area) * (Density of air) * (Velocity)3
• This equates to .5 (0.025 m2) * (1kg/m3) * (10 m/s) = 12.5 Joules of energy each second, which is 12.5 Watts.
The next step is to estimate the percentage of the total Kinetic energy that our turbines extract and turn to electricity.  My guess is 10%.  That means that we get about 1.25W per turbine or 5W total.

It's important to keep in mind that this is a rough estimate.  It's possible that the turbine only extracts 2% of the kinetic energy so we would total 1 Watt.  However, on the other hand the kite is actually traveling faster than the windspeed most of the time, so if our average kite speed is 15 m/s we may total 17 Watts.

## Step 2: Take Some Measurements

My next step was measuring how much power it takes to light up my LEDs.  I cut off a section of 15 LEDs from my long strip and hooked it up to a DC power supply.  (A battery and a multimeter would work as well.  The power (in Watts) equals the voltage (in Volts) times the current (in Amps).  I didn't know how much voltage I could get using my motors yet, so I measured using several voltages from the adjustable DC power supply.  The LED strip is optimized for 12V, but works as low as 8V or as high as 24 (however at 24V the LEDs start getting hot after a minute or 2 which can damage them).  I found that at 12V a 15 LED section (displaying white) uses 2.64 Watts.  At 24.5V it uses 21.1 Watts, and at 8V it uses 0.4 Watts.  Great!  Those look like about the same ballpark as the numbers I estimated the turbines could produce.

When my generators (actually motors) and propellers arrived, I attached some propellers using hot-glue, grabbed my multimeter, and headed to the top of Twin Peaks, the biggest hill in San Francisco, where there was plenty of wind.  I measured the voltage generated by each generator and found that it was about 1.5V to 2V with a strong wind.  I was able to power a 5V LED light strip by connecting 2 generators in series. I also strapped the equipment to my kite and found that the kite had plenty of lift to get everything off the ground.  I found that the propellers spinned faster with their back side to the wind, (opposite of how they would be mounted on an airplane).

## Step 3: Making the Motor (Generator) Mounts

When the generators arrived, I used my calipers to measure them and created a motor mount in CAD using Autodesk's free 123D software.  I added a hole for a set screw to hold the mount in place on the 1/2 inch balsa wood beam and I added two holes for machine screws that secure into the motor's face.  I started by drawing out my design on paper and writing down all the critical dimensions, then putting it into the computer was really quick and easy.  Remember to save often though, since at this point 123D is still in development and has crashed a few times on me.  I added about 0.01" of clearance on the critical dimensions to make sure that things weren't overly snug.

I printed these on a 3D printer out of PLA, a biodegradable corn-based plastic on the Series 1 printer made by Type A Machines and the parts came out great.   I made them pretty solid, using 4 solid layers and perimeters and 60% fill.   The generators fit in snugly and were secured in place with small machine screws on the front.  The hole for the set-screw was just the right size for the screw to cut it's own threads without splitting the layers of plastic apart. I used a small file to smooth out the opening for the balsa wood and that fit perfectly.

## Step 4: Making the Attachment Clips

The beams that hold the turbines are attached to the kite using 3D printed clips.  They make use of a special piece of hardware called a Stubby Retractable Spring Plunger.  There are lots of possible ways of attaching, but this one allows for easy clipping-on and unclipping. To attach, simply pull the ring to retract the spring-loaded plunger, slide it onto the kite strut and let go. I printed them with 4 solid layers and perimeters and 60% fill.

## Step 5: Wiring the Electronics

Be sure to check out the photo comments and wiring diagram on this step.

Basically, I wired the 4 generators in series, each providing about 2V, so the LED strips receive about 8V.  The power goes into the LED controller chip.  The chip has 4 outputs.  Positive, Red Ground, Blue Ground, and Green Ground. I wired 2 wires to each so that I could have one for each of the 2 LED strips.

## Step 6: Flying

So far, I have only flown the kite during the day.  It works great with strong winds, like +20 MPH, unfortunately the winds seem to calm down at night so I haven't gotten the chance to do nighttime light-painting photos yet.  This type of kite isn't the best for carrying weight so it needs a lot of wind to get enough lift.

When flying, All four propellers get spinning very fast and the LEDs turn on when the capacitors have charged up.  It handles pretty well and certainly draws attention at the beach!  It doesn't like hitting the ground though.  I modified my design slightly to handle impacts better by adding a flexible section to each of the two wooden beams.

The next step is to add a battery charger so that I can use my kite-power in various electronic devices.  You never know when you might need some more power!

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## Questions

Very cool! Great engineering!

I'm from India.. Where can i buy a Nexus Prism Kite?

A UFO sighting bound to happen....

Surely the night has brought flying winds to you!!! Please post a kite lite painting!!! Great idea.

as an addicted stunt kite flier (i also have a Nexus Prism) this is a really cool concept.

I'd really like to see a video of how this flies. all that mass has to really effect any kind of tricks other than basic loops. i'm guessing if you try a stall, it'll drop like a rock. I'd also be worried that all that mass would drastically increase the risk of something breaking from a hard landing especially since you need to fly in much stronger winds to begin with. i actually dont fly my Nexus in stronger winds anymore because i broke a wing spar in a strong gust.

are you able to self launch or does someone have to hold the kite?

off the top of my head i'm wondering if you could shed some weight by mounting a generator and prop to the bottom spreader right at the standoffs. the kite naturally focuses air there. let the speader be the structure. you would want to mount the motors in a way that it can pop off when you crash without being damaged or damaging the kite. I did a quick google search and found this. check out the propeller. if you could make something like that out of a flexible material, i bet it would be lighter weight giving you better performance and be much more forgiving to the punishment that stunt kites endure.
http://news.cnet.com/8301-17938_105-10020185-1.html

another thought is rather than having the motors power the led's directly you could incorporate a small rechargable battery pack (use button batteries). the led's would run off the batteries and use the generator to recharge. i bet you could also rig the battery pack so that it could be used to recharge other deivices.

a really cool project ! I'm not the type to do a lot of calculating or drawing before diving into a project, I'm more like, "lets ducktape this motor and lights to a kite and see what happens" to each their own though. My friend Marc runs a haunted house each year, he plans out every part and follows the plan to the millimeter, Our haunted house is built as we go, with only a basic idea of where we want to go, which I admit can be confusing and we some times have to go back and tear down a section but in the end we both end up with scary haunts (sorry but he was just here and we were having this discussion)
I do wish I was more literate in electronics, the flashing lights with changing patterns has to look really wild at night

Fascinating work! Keep developing this. Larger kites are steadier and lift more weight in lighter winds. Google the types of kites used for KAP and it will be much easier to fly in lighter winds. I fly lighted single line kites at night and prefer a delta-conyne because it combines stability and light wind lift, climbs quickly when tugged up through the dead air near ground level and has a broad straight base to prop the kite up on the ground preparatory to a "high launch". High launching means stretching out a lot of line on the ground upwind of the propped up kite, then tugging it up by walking upwind. Once you get through the layer of dead air, you will usually find a very good steady breeze about 150 to 200 ft. up and higher. The night breeze flows smoothly over the dead still ground layer. The resultant steady speed wind, undisturbed by turbulence and thermals makes an amazing difference in how much weight a kite will lift; far more than during the day. A kite will also lift considerably more weight attached to the line 10 to 50 ft. below it instead of on the kite itself. My 7.5 ft.span delta-conyne easily lifts a bicycle generator (actually alternator) attached about 10 ft. below the kite. Phone hookup wires span the last 10 ft. to lights attached to the kite. I'm now experimenting with the very small but powerful electric motors from those small rechargeable R/C helicopters. Connect the wires from the main rotor motor to the tail motor, spin the larger shaft with a finger snap and it will spin the smaller motor. Doesn't that indicate efficiency?
Props work fairly well, but ideally the cambered side should be downwind when the leading edge faces upwind. Consider designing your own blades too, including sailwing construction for the larger slower, torquier ones you might need for single line kites. Google Doug Selsam's generators for inspiration and spend a few hours here:http://www.energykitesystems.net/