Automatic Rewinder Makes Kite Retrieval A Breeze

So you’ve built a fine kite, taken it to the beach, and let it ride the wind aloft on a spool of line. Eventually it has to come down, and the process of reeling all that line that was so easily paid out is likely a bigger chore than you care to face. What to do?

If you’re like [Matt Bilsky], the answer is simple: build a motorized kite reel to bring it back in painlessly. Of course what’s simple in conception is often difficult to execute, and as the second video below shows, [Matt] went through an extensive design and prototype phase before starting to create parts. Basic questions had to be answered, such as how much torque would be needed to reel in the kite, and what were the dimensions of a standard kite string reel. With that information and a cardboard prototype in hand, the guts of a cordless drill joined a bunch of 3D-printed parts to form the running gear. We really liked the research that went into the self-reversing screw used to evenly wind the string across the spool; who knew that someone could do a doctoral dissertation on yarn-winding? Check out the “Reeler-Inner” in action in the first, much shorter video below.

With some extra power left from the original drill battery, [Matt] feature-crept a bit with the USB charger port and voltmeter, but who can blame him? Personally, we’d have included a counter to keep track of how much line is fed out; something like this printer filament counter might work, as long as you can keep the sand out of it.

22 thoughts on “Automatic Rewinder Makes Kite Retrieval A Breeze

  1. Nicely done project.

    TLDR: Twenty years ago a boy makes a sketchy kite string “puller-inner” using a toy motor. Fast forward to present day and he builds a much better one. It winds kite string like a boss. But wait, there’s more!

    – Thomas

    1. Straightforward to estimate pressure on the spool core: 2 x number of turns x force, divided by (diameter*length) of the spool.
      So if there’s 10N on the line and the spool is 4cm dia x 10 cm long, then (say)500 turns would give a pressure of 2.5 MPa (or 25 atmospheres or 375 psi if that’s more meaningful to you). Kinda like a poor man’s COPV.

      1. You’re missing a major disclaimer: that only holds if there is no friction. However, in reality there is a lot of friction! In other words, your estimate is probably at least a couple of orders of magnitude high.

        1. The other way around: This estimate assumes no slip between layers (i.e., perfect friction). But, it assumes the line material stays in the elastic regime, but inner layers are not significantly compressed by layers on top. It’s a spherical-cow kind of approximation, but works OK if there are not too many layers and the string layers add up to a small fraction of the spool diameter.

          But I see how your assumption of zero friction would permit using inelastic string, and give the same result.

          1. Ideally, yes. Consider the case where every loop is independent of its neighbours. All loops will carry their (same) tension and contribute equally (or by 1/r, depending on whether you interpret it as force or pressure). This corresponds to the case of an ideal, perfectly inelastic string wound on a perfectly inelastic spool, where friction is not relevant (or can be assumed to be any value, including zero).

            In reality, as layers build and pressure increases on the inner layers, they (and the spool) compress, relieving tension and acting to slow the rate of pressure increase as the layer count increases. This will only happen if friction acts to limit the redistribution of stress (and thus strain) through the length of string.

  2. Nice, awesome design! Eagerly awaiting the update for the control center to automate the flying of a kite. I envision adding a control servo/motor for the ground plane panning with load/tension sensors as well as some sort of flight, either vision or string vector, sensing to automate the flight controls to maintain position or if undesirable condition real in. Seems the added features could automatically control a kite or even a kite-balloon wind turbine system to operate the system and charge some more batteries. If could fly a kite, I’d buy the system as is.

  3. Seen a similar concept done for reeling in a fishing reel… made for a bloke who had lost an arm. Basically he could put the reel in the device then operate the motor with a foot switch whilst guiding the line with the one remaining hand.

  4. Since the 70’s I remember them using a motorized string hauler on RC gliders, run the string out a few hundred feet and hit the juice. Same as them using small motors with rubber cups on them to start RC motor based planes. Now of course they have RC internal turbo prop planes that require putting a long shaft into the engine to start it.

  5. Neat fun project and I like how he’s completed a childhood invention!
    The guide where the line goes through would wear pretty fast, perhaps add a metal plate or loop screwed to the winder.
    Also could do with some holes in the base to clip onto a chest belt or if on the ground, push tent pegs through… the thought of having a sudden gust of wind sending the winder bouncing down the beach (with charging phone attached) would be a little annoying :)

  6. Man, that brings back some memories. As a boy I bought some blue delta kite and flew it in the backyard. Well the paltry amount of string that came with it would barely get it over the top of our house. That would not do! So next time I was out shopping with my Mother I asked if I could have some kite string. That made it a bit better… but wanted to go higher. Each shopping trip, I’d ask for more string. Eventually my Mother asked, “What are you doing with all this string?” and confessed my intention: “I want to fly my kite 1 mile high”. So she indulged my outlandish goal and kept buying me string.

    Used what little I knew about geometry to estimate how long the string would be based on the angle of the string hanging from the kite when it was in the air. Genuinely don’t know if I got what little math I knew right back then. Today, I realize that it was flawed math as I didn’t account for sag/stretch, etc. Confident I didn’t actually succeed.

    The quantity of string was pretty ridiculous, I used one of my Father’s spent welding wire spools to wind it all up on.

    I’d go out to a church parking lot with my spool and take the kite out till the end of the spool. Standing there with binoculars and even then it was the tiniest faint dot and took lots of hunting in the sky to find it.

    Would take me what felt like hours to wind it all back onto the spool. I remember a man came out of the church and asked what I was doing? “I’m reeling in my kite”, it’s so far out there he can’t see it but can see that I definitely am reeling in something!

    I would have killed to have this gadget as a kid!

  7. What I’ve done is I modified the rear wheel of an old bmx dirt bike into a spool. Now mind you, I fly an 8′ delta kite. The kite string goes around the rear hub and when you flip the bike upside down (don’t need the front wheel any more) you can use a couple of u-shaped spikes to hold down the handle bars to the ground. Then you can pick up the back of the bike and aim it where you want the kite to go. Let the rear wheel free-wheel as the kite spools out and use the coaster brakes to monitor the release speed. Clamp a vise-grip on the edge of the spool when you want to lock the spool. When you’re ready to bring in the kite, just turn the pedals by hand and re-aim the bike in-line with the kite as needed so the line doesn’t drag too hard on the side of the rear wheel/spool. Basically using an upside down bicycle as a kite spool.

  8. Excellent and well done!!!

    One thing, here in Gold Coast, Queensland, Australia, most kites flown at the beach are TWO (2) strings.
    Sometimes called acrobatic or stunt kites they are cheap things sold even in supermarkets.

    With two strings you can control the kite side to side and up and down and everything in between. Quite a lot of fun and entertainment.
    And at dusk put a few bright LEDs and it will look just incredible!.

    Sooooo … a big improvement/update to this tool will be to wind up two (2) strings together :-]

  9. I hooked my son’s kite up to a fishing rod (well the bottom half). I even just used the line already on it which was a higher test line. It works surprisingly well and you can even set the drag to let it pull itself higher when the wind is strong enough. When it is high enough turn up the drag and real it in when you are bored.

    We recently discovered two line stunt kites which are so much more fun to fly but require two fixed length strings. My fishing rod trick doesn’t work there and winding the strings in such a way that you don’t add twists is annoying. Might need to build something. The kite would have to be on the ground first so nothing quite as elegant would be needed.

    1. Always hold your winder in the same hand when wrapping and un wrapping you lines if you want to avoid twists. I flew tractin kites for quite a few years, you get used to it. “Which hand do you wind with?” is a common question when you’re helping other pack up traction kites.

  10. I’ve seen the autoreversing screw thread being used with a small, elongated and rounded -diamond-shaped shuttle bar, hinged at center, so it can go around the curves at the end but not take a “corner” at the crossings midway. A 2d-example can be seen in this maypole braiding machine:
    https://youtu.be/WlrzuZpJ2N8.

    With two separate points, there would be no way to prevent reversing midway.

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