Kite Aerial Photography - Simon Harbord's KAP Rig

Notes on Kite Aerial Photography: Others

Simon Harbord's KAP Rig

Title Sheet for Simon's schematic diagram set. I know the small inline versions of these diagrams are illegible - click on them to see the ones you can read. (62K jpg)

As noted in teaser of the previous page, Simon's KAP rig squeezes several functions from a two-channel radio through the ingenious use of electrical components. His approach, based on a pendulum suspension as opposed to my Picavet, looks like it would be fun to build. On this page he describes how to go about it.

Simon's field kit including hand truck, winch, and dog stakes. (67K jpg)

APPROACH

The adjacent image is a scan from an old photo showing all the ground gear, the winch with overlever band brake, the KAP rig on the ground to the left, numerous dog stakes for holding the winch down and pegging out the line etc. (Note the leather palmed gloves!) The whole lot packs up into the cases and straps onto the winch for transit with a neat waterproof cover so that the winch and all the gear can be wheeled to the location and deployed in minutes, the kite being in its own bag already fastened to the winchline.

I guess I came at KAP from a different angle, starting with balloons as lifters, where weight was at a premium, and camera's HAD to be lightweight, and the only answer to tilt/ pan was direct from the R/C servos. Then I discovered big lifting kites and started to trade off low weight for robustness and the ability to get motor drive SLR's and video cameras into the air. En route to this approach I found that R/C servos and gear arrangements just couldn't take the strain of rotating anything over compact camera size, and the whole approach took on a rethink.

In going up a scale to big kites, and excess lift, I found a nice set of serendipitous aspects which were not possible on the small kite/compact camera side of things. Once you need a winch and thicker line (would you believe 4mm) you can start to use other approaches. One of the best discoveries I made was all the rope handling gear available in mountaineering and yachting shops. Best of all these goodies is the JUMAR. With a jumar(smallest size available)attached to the top of my KAP rig I can clip the rig onto and off the line in no time at all once the kite is up and pulling, -reach up, clip, -its on. The little teeth grip the line without damaging it, a miracle device....

Once things are up in the air, I apply the winch brake and then using a line walker and dog stake, peg the kite in the right part of the sky, as sometimes the launch location doesn't quite fit the aspect required for the shots, eventually when things are right I start snapping away. Essentially I avoid handling the kite line, and simply NEVER take the kite line strain in my own hands without knowing I can let go and have the winch brake take up the strain. Very early on I had a real bad time when a squall hit and I was handling line, a very awful feeling knowing that you don't have the physical strength to do a thing. After that I developed the various hands free aspects.

Sheet 1. Schematic layout of rig - elevation view (left, 38K jpg) and Sheet 2. Layout of Control Unit (right, 56K jpg)

The RIG

Anyway back to the rig, I always had an interest in "systems" but hated control systems where all the control lies in a little black chip with no "explicit" control to get tinkering with. I accept the wondrous little black boxes that make up the R/c sets, but like to work at the electromechanical rather than the electronic level. When I started to realize the limitations of R/C servos and various gearing arrangements, and started to get less constrained with weight, I began to think about using the servo's as precision controllers for switches to control pan/tilt motors.

Sheet 3. Schematic of rotary switch (left, 41K jpg) and Sheet 4. Rotary switch wiring diagram (right, 68K jpg)

Photograph of Simon's control box (23K jpg)

ROTARY SWITCHES

Then I discovered the wonders of multiway rotary switches- (really giving away all my secrets now...) These can be picked up from Radio Shack or similar for pennies. Remove the little ballbearing/spring locator which makes it stiff and clicky to operate and you have a smooth rotary selector switch which will be turned by a servo with ease- no strain on the poor little servos any more. Working out the wiring for such switches to control motors is a lovely mental exercise in logic rather than electronics, wiring in the limit switches to stop motor overtravel is all part of the deal. What you end up with is a compartmented box 3x2x5 inches containing batteries, recharging socket, servo/ switches controlling all functions, receiver and a connector on the bottom (use a computer serial or parallel multiway socket) Attaching to this socket outside the box is a plug and ribbon cable going to the motors, shutter trigger, light, limit switches etc. All the wires clip nicely onto the frame and all looks neat and tidy. Makes the whole thing modular, you can unplug the camera cradle and motors from the control box and work on each separately.

Sheet 5. Exterior (left, 62K jpg) and Sheet 6. Layout of Control Unit (right, 56K jpg)

Photograph of Simon's transmitter with rotary potentiometers (17K jpg)

TRANSMITTER

Of course, radio transmitter joysticks aren't very good for precise control of multiway switch position due to the configuration /spring lever action. Open up the transmitter, look at the potentiometer under the joystick, revamp, discarding the joystick and just use the potentiometer, or a similar more suitable one of the same resistance, fastened onto a plastic backplate where the joystick used to be, attach a pointer knob, and mark a scale next to the knob with the various servo positions/ functions marked. Lo and behold -a custom transmitter with 2 knobs (channels)and as many functions available as you can wire into your servo controlled multiway switches. I use a resting position for the motors with an ultrabright LED on the mid throw of the servo such that I can calibrate my knob position with the bright LED and know that the motors aren't moving. The possibilities with a 4 channel set are outrageous in terms of available functions.(so I stuck to 2 channel- its cheaper. )

I use a drogue to maintain some directional stability on the rig, and the Jumar arrangement only allows very limited rotation anyway.

Oh, the motors, didn't I mention - high torque, low speed, reversible, professional looking, inexpensive, not too heavy as long as you power them from the control unit - barbecue spit motors. They're a dream.

Sheet 7. Pan movement motor mount detail (91K jpg)

NOTES

The ultrabright LED got removed from the rig at some point as it ultimately served no useful function, you can see where it used to be, there's a hole in the control box marking its old location, I'd forgotten when I posted you early on that it'd gone. Function was to light when the rotary switch was in neutral. However, it was replaced by an altogether more practical approach, simply, this was to set the to controls to the desired neutral position, open the box before flight and use a little tiny aluminium spanner made out of some scrap metal to turn the rotary switch manually to the same function position, the friction fit of the connector with the servo allowed it to slip enough to make the adjustment. This adjustment was only occasionally needed, probably as a result of electronic "drift". You'll probably also spot a small socket and spare wires at the bottom of the control box, this was another bit that was put in to provide some extra functionality if it were needed. The whole thing was a bit evolutionary, and changed from week to week as I resoldered the switches in new ways.

Photograph of pan and tilt motors (left, 16K jpg) and photo of the entire rig (left, 18K jpg)

One thing that's been worrying me from the point of view of others is the shutter release, as I used the Olympus motordrive, the wiring layout was set up specifically to provide the short across the shutter leads to fire the shutter. I realize that many KAP cameras do not use this approach, and some may still wish to use a servo.Though using one would take away many of the advantages of a modular design etc,.and with a two channel set this would immediately remove some of the functionality of the two switch approach, nevertheless, a single rotary switch would still provide left/right, up/down and neutral though only at one speed. No real loss there, though I personally would still use my approach and work the shutter with a tiny motor/cam arrangement or a small solenoid or similar, rather than a servo, keeping all the radio gear in the one place. One thing you can't live without is the microswitches, as the spit motors are very powerful.

How long will the cradle operate?- I used to change the batteries out when the motors sounded tired, that didn't come around that often, the D cell that the spit motor is designed for is supposed to turn a chicken for hours and hours, the AA batteries seemed to cope for several flight sessions, I think I used more batteries testing and developing than in flight...!

QUICK LINKS to other Simon Harbord Pages:

Introduction to Simon Harbord
A Gallery Page of Simon's KAP Images
Simon's Guiding Light
Simon's KAPisms

Comments to author: crisp@socrates.berkeley.edu . All content, graphics and
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URL: http://www.ced.berkeley.edu/~cris/kap/others/shrig.html