Energy harvesting KAP rotator

Many of the discussions about stabilizing involve dissipating energy in the rig. I got to thinking how this could be put to good use. So here is a rig that I made that uses the energy from swings of the pendulum that occur along the kite line. It translates that energy into small rotations, in the manner of an auto-KAP rig. The device walks around over the course of a few minutes, or it can be deliberately rocked back and forth to re-orient by pulling back and forth on the kite line. This works better than you'd think.
Here's the device.
KAP harvesting rotator

For rotation, no servos, no electronic position control, no rubberbands or silly putty or batteries or propellers or programming skills required. It doesn't do tilt though, only pan. (Hmm.....)

It's 3d printed. You can buy it here (there are more pictures too) in case anyone would like to play with it:

Here's a video with music done by me. It includes the tune to a nursery rhyme that seemed appropriate at the time (kinda late last night).

I'm charging a small markup ($5) in the hopes of breaking even on my prototypes.

Anyone seen a rig like this before?

The pendulum rod is made from a threaded nylon rod. This is not ideal since it is bendy and springy. I've been thinking about using a carbon tube instead but the rod was easier to get for now. I'm open to suggestions.

I've included recommendations by sparrowscope concerning UV and inspecting for cracks. It doesn't have filleting that he's recommending though.

The tricky part is that you have to estimate the line angle and lock it in before you send the rig up. You can just let it hang on the line before locking it down. But if the line angle changes drastically, the rig won't turn. If the wind is really messy, the rig can turn too fast and not have time to get good shots. But I think that kind of wind would also not yield sharp shots anyway. I haven't flown with a very high angle kite like my delta yet. There's a limit to the line angle that this rig can handle before it would need a different hanger, which would be easy to make. I had no problem with my Rok, and I think the levitation delta would be ok too, especially with a tail.

I've only had one field session with it so far, so it's still young but I was so excited by how well it worked that I wanted to get the idea out there. I was also surprised how fun it was to control.

Do you pendulum users use tugs on the line to help get the pendulum to stop swinging? It seems like this works to some degree.

The mechanism seems plenty sturdy for my S95, but a heavier camera would need a sturdier one. I'd be willing to scale it but Shapeways charges by volume so the price goes up as the cube of the scale factor! Maybe you have access to a 3d printer. Another idea is that the teeth on the toothed ring reminds me of a hole saw; it's conceivable that this type of rig could be done with one of those too.

One thing that I don't like is how inconvenient a pendulum is to pack, compared to a Picavet. I wonder if anyone has used folding or telescoping or easy disassembling ones. I've been eyeing my umbrella but it's a nice one that I don't want to repurpose yet.


  • edited April 2013
    Wow! Outstanding and really brilliant. Thanks for sharing both the report and the item.

    Just asking, could the teeth be made smaller to respond to even smaller inputs? So many of us are using other means to absorb the energy that not much is left over. Or...this is really stretching it...can the motion absorbed by your device be used in something of a soft, damping manner - probably not?

    Good going on this thing. Awesome.
  • Nice little semi-random walk device. There are quite a few wind powered devices out there, but this one beats most for simplicity and for the static periods. It would be pretty impossible to making good panos but you could get a lot of good random shots.

    I think I'd just do 3D printing for the mechanism. Coat-hangers and kite spars . . .
  • Sweet. I love simple mechanical mechanisms. With a folding pendulum the whole lot could fit a pocket.
  • Awesome! :)
  • edited April 2013
    Ingenious :)

    And wrt packing pendulums -- just pack it together with your (sparred) kite.

  • Thanks for all the encouragement.

    @Phil (AerialLensGuy): Yes, the teeth could be made smaller. I wanted to err on the side of making it chunky so that the print resolution wouldn't affect it. But I used shapeways and the resolution is fine. It could probably be pushed by 2x.
    If resolution were a problem, the toothed disk could be made larger in diameter. For reference, today I measured about 10 degrees each way to get a solid move to the next position. There are 15 positions. Half clicks are ok too. (10 degrees in only one direction).
    Increasing the resolution means that static friction could become a problem. But since my current "bearing" is just a metal washer, this could be improved if need be. (Like a teflon washer maybe).

    The point about your rigs not swinging much: your camera is not rocking but the connection at the line is rocking, no? The camera must stay put briefly due to inertia if you tug on the line. It's great if it's underdamped. Then you have a better chance at getting only one click (or half). Maybe there's a clever way to insert this thing in your suspension. Can you point me to a picture of your latest suspension?

    @FCB: "impossible" sounds like a challenge! :) I assume you mean a horizontal panorama with a vertically ("portrait") oriented camera, which is much harder (more pix) than a horizontal camera. Is that what you meant? I think it wouldn't be too hard to get a panorama of horizontals.

    @Simon: Do you know of any good designs for a folding pendulum?

    @sebaska: I often take bike rides and soft kites are prefered. Also, I'd prefer not to disassemble it, at least the top part. Maybe I should just take off the bottom.
  • FCB
    edited April 2013
    The best panoramas (horizontal panning) are made from a relatively rapid series of shots in smooth consistent wind. This gets you a consistent XYZ camera position (pictures taken over a short time period) and relatively stable platform for sharp shots (no wild pendulum swings).

    Since you have to wave the pendulum to switch positions, it will be harder to get the pictures in quick order or harder to have a stable platform for each shot. At higher camera heights and in stable wind it might not matter, but for low elevations (closer to the subject of the photo) getting a good panorama with the rig will, IMO, be very very difficult. Bright light and short exposures might get you there but it won't be elegant.

    BTW -- I still think the concept is super cool for it's simplicity! Very cool!
  • I think a folding pendulum could be made similar to tent poles with bungee cord. Pins could hold things together. Essentially just ferruled rod, same as kite spars.
  • Very clever. All on a Saturday night.
  • edited April 2013
    I used an old telescopic aerial (from a 35MHz r/c transmitter) in this simple rig for a Mini-DV-808 camera
  • Dave: That's a good idea. I was thinking along those lines. But now that I see your pictures, it got me thinking. With an aerial, if the top rotates by 24 degrees (one click on my mechanism), it's not clear to me that the rotation will make it all the way to the camera. You could try it for me. But it might also depend on the specific one used, lubrication, maybe temperature, inertia of camera (S95 in my case).
  • You're right - there's not a lot of friction to prevent rotation, particularly at the top of the rig where the aerial cross-section is smallest. That doesn't matter with my rig since the 'tailplane' at the bottom is designed to ensure that the camera mount stays oriented in the same direction relative to the wind.

    However it is possible to squeeze the upper, lower-friction sections of aerial tubing slightly into an oval cross-section to prevent rotation.

    As well as R/C aerials there is another other source of telescopic metal tubes - those handy gadgets with a strong magnet at one end for retrieving small metallic objects from inaccessible places (the bargain tool stalls at local markets in the UK often sell these very cheaply)

    One advantage of the r/c aerial is that it has a threaded hole at the 'large end' ideal for attaching a camera support.
  • I was going to mention telescopic aerials, as I too experimented with them, but after having one fall apart in testing, and taking another to bits, decided not to mention them, and instead mention the ferruled rod with safety pins. I really can't recommend telescic aerials for hanging a camera from. Take a spare one to bits and you'll see the weakness of the components. They really won't take mechanical stresses.

  • edited April 2013
    You're probably right Simon (well, no, you definitely are right) - at least for a rig that was intended for a 'real' camera. But for things like the Mini-DV-808 camera it's fine - I've no doubt the camera itself would survive a fall of several hundred feet if the aerial came apart.
  • Dave,

    That link to the camera doesn't work.

  • edited April 2013
    It wasn't a link actually - the hash/pound sign is part of the common name of those things, but put one in html and browsers think it's a link. I've replaced it with a proper link.
  • edited April 2013
    Nice design...but I do my best to ensure NO movement of the line when shooting...I like the silly putty/ rubber band 'cos it's smooth. This is jerky by definition! So....I'm not sure if this helps, but a wind vane might provide a 'rock free' drive: the escapement would ensure progression of the the fan tail on a windmill?

    Oh and a note on pendulum joints: I use a length of theromplastic tubing for car hydraulic hoses riveted to 6mm and 9mm aluminium tube, it forms a semi rigid joint that is free to move in all directions :

  • edited April 2013
    this is awesome. I saw an out of patent windmill-driven line climber on the a few weeks back. If you're 3D modeling these, then this design ought to provide some fodder. Note its cool transmission for powering back down the line when it hits the top:

  • The title made me think of this picture I recently saw. Nothing to do with KAP, just kites.
  • edited December 2013
    Hmmm.......... I must go have a look through my old tripods, large and small, and weigh the legs. I have thrown them away in the past, having removed the head and centre section for fitting into aluminium masts for pole work.
  • Found an old monopod with a screw-on foot.....this can be removed for fitting a frame with no hassle.....but I am sure that this has already been reported on these pages ;o)
  • I made of version of Hobbiestoomany's energy harvester and gave it a preliminary trial this week. It sort of worked, but it was not flying, just hanging on a fixed kite line. I think it has potential, but the results are going to depend on the circumstances of the flight. It requires a particular type of line jerking to make it rotate just the right amount. The escapement could be modified in many ways, so there is much fine tuning to do. There is a note at Public Lab about it: Thanks much to Hobbiestoomany for sharing this idea.


  • Hi, thanks for the revival of this matter,... I will try because I see that some components already available can be good for purpose,...
    I have tried and not completed testing of a RIG that has a continuous PAN rotation wind-powered; a modified feather or a drogue is rotating component, a worm-gear taken from an automotive rear wiper ratio near 1/50 and the RIG TURNS until wind is blowing
    Also Bob Dylan suggested that the answer in BLOWING IN THE WIND,...
    SMAC from Italy
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