KAP Rig No. 4

KAP Rig #4 is a midweight, four-channel camera cradle designed around the S100 Canon Digital Elph point-and-shoot camera. The rig ended up at 1 pound, 9 ounces and has been fun to build. Where previous rig descriptions have emphasized the finished product I will make a more leisurely accounting of construction process in this report. I bought this Canon Digital Elph (the original model in what is now a large family) around two years ago. It has served well on the ground and reached around 7,500 images on the exposure counter before its mid-career shift to aerial duties. The build quality of the Elph is superb and while diminutive it is also a dense little thing at 9 ounces. .

KAP Rig #4 sits on the ground before its maiden flight in La Jolla, California (Canon G1, April 2002).

For years I resisted the urge (I am gadget prone after all) to build a KAP rig based on a digital camera. There were certainly reasons for this. Chief among them was the fear that I would have the luck to capture a "killer KAP shot," say a bird in the foreground or a fine sun glint from the lantern of the Campanile, and it would be in a frustratingly low resolution digital format. Over the years the cameras have improved, becoming a great asset for WWW and desktop publishing.. But only the very high end models produce a magazine cover level of quality. It is also my impression that digital cameras tend toward slower shutter speeds. I know that I can amp up the gain in my Canon G1 but it comes at a visible cost in quality. Then there were a few technical problems like overriding the typical digital camera's desire to time out (shut off) after 3 minutes of inactivity (available as a menu item on the Elph) and the complexity of figuring out interface pinouts. Nevertheless, in April 2002 I spent a couple of weeks putting together a digital rig around the modest 2 megapixel Digital Elph and I am delighted with the results. I may never look back.

My first dozen images from the KAP Rig #4 were worm's eye views from the ground. Every attempt at a maiden flight was thwarted by the absence of wind. We finally got aloft during a trip to La Jolla in Southern California to check out the UCSD Engineering program for Charlie. But let's back up a couple of weeks and see how the rig came together.

Photographs of rig components as they were being designed / built. from the upper left clockwise we have my project box full of pieces and components in progress; my first scratch cross beam and its successor; the rotation axis and gears (before conversion to continuous rotation); and a corner bracket with threaded insert for the antenna boom. (Canon Digital Elph, April 2002).

Like each of my KAP rigs, the Digital Elph rig was built from the inside out. This is to say that the construction begins with locating the center of gravity for the camera as it lies on its back plane. I did this by making a u-shaped shell to contain the Elph and then balancing the back plane of the shell (with the Elph inside) on top of a marble. The point thus established becomes the center of rotation for the image format (portrait/landscape) rotation bracket.

Once the format rotation bracket was balanced and built I could set about making the tilt rotation U-bracket. This bracket can adjust the camera to point from straight down through the horizon. The process involves 1) making a crossbeam and support arms, 2) temporarily mounting the radio, servo, and battery carried by this arm as well as the format rotation bracket with camera, and 3) determining the center of gravity for this assembly. The points on the support arms where this subassembly balances define the rotation servo axis and pivot location.

Rig components toward the end of construction (Canon Digital Elph, April 2002).

The final U-bracket is then constructed to hold the plan rotation servo. In this case everything is assembled and the crossbeam is balanced on the eraser end of a pencil to located the position of the plan rotation axis and the vertical 6-32 machine screw that attaches to the Picavet suspension. Paying careful attention to balance in the construction of this rig lessens the load on the servos and allows battery charges to last longer.

KEY	Description
1. Plan rotation axis	a 6-32 bolt constrained by an aluminum spacer inserted through the wood crossbar.
2. Plan rotation gears	at 1:4 ratio these are adapted from RC car parts and mounted on an normal Airtronics 94102 servo, this is my first cradle with a servo modified for continuous plan rotation..
3. Radio receiver	Six channel FM radio receiver (four used)
4. Radio antenna and support boom	The support is made from carbon rods (tent pole shock cord technique) with the antenna wire wound around the exterior of the support.
5. Tilt rotation servo	a normal Airtronics 94102 servo used in direct drive
6. Horizontal / vertical format rotation	a bracket pivoting on a thrust bearing taken from an old floppy disk drive.
7. Camera attachment	I made a u-shaped aluminum shell for the camera and secure the camera inside it with a 1/4-20 nylon bolt threaded into camera tripod socket. Elastic cord is used for a keeper to keep the bolt nearby when it is not installed.
8. Format drive train	nylon gears are used to drive format rotation - coupled to normal Airtronics 94102 servo.
9. Shutter release	HiTec HS-80 servo with plastic horn to serve as "pseudo finger" for shutter release.
10. Power source	6.0 VDC, 600 mAh Ni-Cad battery pack made with high-capacity AE cells.

At this writing I've only flown the new rig about two dozen times and it has worked like a champ with over two thousand aerial images taken. So far, so good. I will keep you posted as I gain experience. I have also purchased a Nikon Coolpix 5000 with 19-mm and fisheye accessory lenses. I can hardly wait to get this camera aloft.

I have now flown KAP rig No. 4 on dozens of outings and it has performed quite well. I am also delighted to report that it has carried three versions of the Digital Elph (S100, S200, and S300) without modification with a tip of the hat to Canon for keeping the basic camera geometry constant). I just added thumbnail gallery pages with example images from the three Elves/Ixii:

If you would like to learn more about the various Digital Elph models, or any other digital camera for that matter, I can highly recommend Digital Photography Review -- check their reviews and the forum section.

Comments to author: crisp@socrates.berkeley.edu . All content, graphics and
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KAP Rig No. 4 Canon S100 Digital Elph

KAP Rig No. 4
Canon S100 Digital Elph