KAP Rig No. 2

Notes on Kite Aerial Photography: Equipment

KAP Rig No. 2
Canon Rebel X SLR

Your author launching KAP Rig #2. Claudia suggests the appellation "Bigfoot". (50K jpg, November 1996).

In my experience one of the great joys of being an adult - say as opposed to a young college student - is the ability to treat oneself to the accouterments of a hobby or interest. So it has been with me lately. As I developed my experience with KAP Rig #1 I became increasingly enthusiastic about taking photographs from kites. I enjoy my Sunday outings and the anticipation associated with the processing delay. If I go more than a couple of weeks without taking shots I start to get grumpy. So as I started to grow a bit weary of the constant view of the Yashica T4's 35-mm lens and the constant horizontal format of my images my mind turned to alternatives. What would it be like to shoot with a wider 24-mm lens? How would my images differ if I could shoot in vertical format? How about the super-wide fisheye lens that seems to be popular with our Japanese colleagues? In July 1996 I decided to find out.

I started out by looking at 35-mm, single-lens reflex cameras (SLR). These seemed to offer the most reasonable path to wide angle views. Rangefinders with sufficient quality are very expensive while the consumer grade SLR market is more reasonably priced. Like Anne Rock before me, I eventually decided on the Canon Rebel camera. It was a tough decision because my terrestrial gear has always been Nikon. Nevertheless, there were some compelling reasons. The Canon Rebel X body is very light - only 3/4 of a pound. At most other times in my life I would have held it in my hand and thought "what an insubstantial piece of plastic this seems to be." With KAP purposes in mind I held it and thought "ooooh, mmmm" and then smiled and bought one. I've since found it to be a very satisfactory camera for its roughly $200 price tag. I also purchased a 24-mm wide angle lens with lenshood and a 50mm standard lens.

The next step was designing and building a cradle for the camera and here I was influenced by my earlier visit with Wolfgang Bieck. Wolfgang built his rig "right side up" as opposed to my earlier "upside down" approach. He also incorporated a set of tripod landing gear for those occasional unscheduled touch downs (I have had about a half-dozen of these in the last two years including one last weekend - so far no damage). Wolfgang also used an electronic relay to fire his Minolta SLR shutter. The images below show how my rig turned out.

Front view of KAP Rig #2 (26K jpg, November 1996).

The components in the Canon Rebel-based rig include:

1. A HiTec HS-615 MG servo drives plan rotation through 4:1 gears normally used for a radio-controlled car.
2. A 6.0VDC, 600 mAh ni-cad battery pack made of small high capacity AE cells.
3. A HiTec HS-615 MG servo provides tilt rotation via direct drive.
4. Two carbon fiber legs for the rig tripod.
5. The Canon Rebel X shown with 24-mm lens and lenshood.
6. A 3/32" sub-miniature stereo plug connecting the camera's remote jack to a radio-operated relay (see below).
7. The third carbon fiber tripod leg carries the radio antenna.
8. Nylon gears at 1:1 to drive the camera's rotation between horizontal and vertical format.
9. The radio receiver rides on the tilt rotation bracket.
10. The third HiTec HS-615 MG servo drives the format rotation gears via a torque tube.

The general construction of the rig follows KAP Rig #1 in using a combination of aluminum angle, basswood, and model aircraft plywood - all materials I've worked with before. The horizontal structure is 3/8" basswood which is light, strong and easily worked. The vertical components are from 1"x1"x1/16" aluminum channel reinforced with 3/32" plywood. It turned out to weigh just over one pound without the camera. I strive to keep my weights down because that allows a small kite, thinner line, and less stress on the organic anchor (me.)

Front and back views with the camera rotated into vertical picture format position. (27K jpg left and 31K jpg right, November 1996).

These views show the rather sparse construction of the rig. Radio, relay, and battery are attached with Velcro and cable ties to the horizontal bar of the tilt bracket. Having the tripod landing gear has been nice for it allows the rig to stand upright when fiddling with it, after preparing it for launch, etc.

Servo arrangements for plan rotation and tilt rotation (24K jpg left and 25K jpg right, November 1996).

In the left image you can see my revised arrangement for the plan rotation access. As before I used a long 6/32 bolt (from a toggle bolt) for the suspension point. All hangs from the wing nut that attaches this to the Picavet cross. To constrain the bolt I thickened the wood at the point of rotation and inserted an aluminum spacer through the wood to serve as a bushing. The end of the bolt has a nylon spacer that serves as a low-friction bearing block on the end of the aluminum spacer. It seems to work well and it was easy to build.

The large white gear only turns 90 degrees. I kept the entire gear and mounted it to the servo horn just slightly off center. That allows me to adjust the gear meshing by where I place the large gear on the servo spline. Speaking of servos, I treated myself to the HS-615 MG servos which run around $45 each ($75 list price) because they have high torque (107 oz./in.) and double ball bearings for smooth operation. They have been really nice to work with.

The right image shows the tilt rotation servo and its connection to the tilt bracket. The HS-615 MG servo has plenty of torque for this application. The photo also shows my plywood - aluminum lamination.

The relay that fires the Canon's shutter (38K jpg, November 1996).

One interesting aspect of the Canon Rebel is its small side-mounted electrical jack for remote control. Triggering the shutter by electrical circuit makes for a less complicated rig because you do not have to mount a servo outboard of the plan rotation, tilt, and film format movements. Being an empiricist at heart I decided to figure out how the remote jack functioned and put it to use.

The remote jack accepts a 3/32" sub-miniature stereo plug. My local camera dealer kindly (amazingly?) let me disassemble Canon's wired remote to check its workings. Sliding the remote's switch halfway closes a circuit between the stereo plug tip and the plug base. I assume this is the equivalent of pressing the shutter button halfway for exposure and focus lock. Completing the travel of the remote's switch adds the middle band of the stereo plug to the circuit. The camera's shutter fires when all three "zones" of the stereo plug are in electrical contact. The Canon can be placed in a mode where only one exposure will result from this type of switch closure no matter how the closure lasts. There are no electronic components (e.g.; resistors, capacitors) in the remote and the remote has a thumb lock for "bulb" exposures suggesting that prolonged closure of the circuit is acceptable.

The next challenge was finding a means for the radio receiver to produce a similar circuit closure. Here I used a electric sailplane on/off control made by High Sky (203 Bison Ridge, Nappanee, IN, 46550, 219-773-4705). It is slightly larger than a box of matches and weighs 1 ounce -- about the same as the micro servo it replaces. High Sky's device is basically a small relay that can be actuated by any radio channel (I use rudder). One end of the device plugs into the radio receiver. At the other end you can connect two wires to be either a normally-open or normally-closed circuit. For firing the shutter I built a cable that connects the sub-mini stereo plug tip to plug base to one wire and the stereo plug's middle zone to a second wire. These wires are then routed to the normally-open connectors on the relay. The relay has a small potentiometer that is turned to adjust the point in the radio channel's range where the open circuit (shutter off) will transition to a closed circuit (fire shutter). The adjustment is sufficiently accurate that I use my rudder channel's trim tab for firing the shutter.

My High Sky relay has been used for about 10 rolls of film so far and it has worked fine for me. The one thing I would change is using a right-angle stereo plug that hugs the camera body but I have been unable to find one. I bought my High Sky on-off controller for approximately $20 from Sheldon's Hobbies in San Jose, California (800-228-3237). It comes with brief but adequate instructions.

The rig in low-level flight (32K jpg, November 1996).

At this writing I've flown KAP Rig #2 about 10 times and everything seems to be working quite well. It doesn't seem to take a great deal more lift than the previous rig even though it is twice the weight. I had a bit of difficulty trimming the horizontal / vertical rotation positions but have now solved that by using a computer radio. The pictures coming out of this apparatus are entertainingly different than those I was able to capture before and that makes it seem quite worthwhile.

Comments to author: crisp@socrates.berkeley.edu . All content, graphics and
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URL: http://www.ced.berkeley.edu/~cris/kap/equip/kaprig2.html

KAP Rig No. 2 Canon Rebel X SLR

KAP Rig No. 2
Canon Rebel X SLR