Experiences and Techniques - Email Excerpts

David Woodhall, Johannesburg, South Africa       March 13, 2001

The rig which was made as a temporary thing has not changed! As a bit of background I am a radio ham and 25 years ago I made a dish antenna for receiving meteosat transmissions that was propped up on bricks as a "temporary" installation. Despite moving house in this time the "temporary" installation is still there. This may give you an insight as to why the KAP rig has not changed!

The object of putting this together was simply to have FUN. At my work we buy in CCTV cameras and we manufacture microwave and radio equipment. I had all the parts except the kite and put that right before Christmas. I think I mentioned that I bought a delta of about 11 feet span and borrowed a delta conyne of 9 feet span. There seems to be little difference in their performance which actually surprises me as I had hoped that the bigger delta would have more lift in the light winds we experience in this part of South Africa (Johannesburg).

The rig consists of a pendulum mounting with the camera and other parts at the end. That sounds grand but what it means (see picture) is that there is a piece of dowel about 60 cm long with a camera BOLTED (wow that's not really temporary- must make amends) to the end of the dowel on an adjustable mount (piece of tinplate that can be bent). Above this is a 12v 400mA nicad battery pack and above that a small 2.4 GHz video and sound transmitter. The battery pack and transmitter are also fixed to the dowel - they use masking tape to fix them to the dowel - that's just fine for the temporary project! The rig weighs in at 450 gm.

The Rig The camera is a low cost colour CCTV unit with a small fixed lens. The pictures from this are really amazing considering the size and cost. I have a couple of lenses that I can change and have found that the longer focal lengths give slightly better results with a smaller field of view. As probably can be expected this lens shows up the camera movement much worse than a wide angle.

The video transmitter has a small antenna fitted to the top of it that sends it's signal unidirectionally so it does not matter which way the kite faces.

The battery pack runs the transmitter and camera for more than 90 minutes and this is just fine as I use an old VHS-C 12 volt video recorder on the ground. The recorder takes a 45 minute tape and I have normally just left the recorder running as I experimented with the kite and settings.

The other ground equipment is a matching receiver to the video transmitter that has a built in directional antenna. This is popped onto the roof of the car and pointed in the right direction to pick up a signal. The flying field I have used for the tests is about 7km from my home in a straight line and one day I set up another receiver at home on my amateur radio mast. Pictures were picked up from the kite when it was about 25m off the ground and the quality was very good. This shows that height matters with the radio transmitter as we sell this equipment to cover about 1.5km under normal circumstances.

Now you can see that I am combing two of my three main hobbies! The third is radio controlled models and you can probably guess that the camera has already been installed in a helicopter and a plane!. The kite results are much different and in some respects more challenging.

. The biggest problem with what I have done so far is that the camera mount is no where near as good as it should be. With a still camera the movement of the pendulum would not be a major problem. This can be seen from the pictures I have enclosed as they are effectively still images taken from the video footage. I played the video tape back through my PC and used a low cost video capture board to "grab" images when I thought the pictures were fairly good. If you sit watching the moving video images the picture really jumps around, sometimes quite violently. I think I need to invest some time in making a Picavet suspension. I have tried recently to get small pulleys but can't find what I want. The model shops in this area do not cater properly for the marine enthusiast and I will probably wait till I go to the coast to get what I need.

The KAP pictures are not as good a quality as the original video. I am using a low cost frame grabber and simple program that does not do justice to the source material. One day I may fly a digital still camera just for the heck of it. I have a Sanyo one that is quite old and does have the facility to take pictures when triggered from an external RS 232 source. All I have to do is figure out the protocol to the camera from a PC and then I can emulate this with a small microprocessor or even through a radio link.

Video Capture Image Well that's a run down on what I have done with my temporary rig and how pleased I was with the results. From the couple of pictures included you can't get an idea of the FUN that my family has had getting these results! We have been to the flying field only about 5 times and each time have made the results just that bit better. The biggest improvements were to make the pendulum longer (started off at about 25 cm) and also to put the pendulum at about 25 m away from the kite which flies on a 100m line.

The other biggest improvement was to choose days where the wind was strong enough! Sounds obvious but when a temporary(!) arrangement has been made to fix the camera to the line, you have just got to try it that weekend! The Winds here in our summer time are quite light and range from zero to about 10 mph maximum. The best results were obtained with winds from 8 to 12 mph. I think the lift from the delta is just about right at this level. The rig weights 450 grams and I tried to lift 1kg of water on a windy day. The delta managed this very well but the pull on the line was just a little to much for safety and I did not put on the camera that day.

I want to add a couple of servos and a receiver to the rig so that I can move the camera where I want. This is going to increase the weight over the point where the delta will lift it all safely in light winds. This means that I may have to make a "temporary" arrangement to put together a radio controlled camera that can be exchanged with the original "temporary" rig. Something to ponder about in the coming days.

David, hope this is of interest and if you want some more info on the temporary projects please just send a mail.

Your web site provided me with some of the ideas and a lot of FUN reading. Hope this note can be of some use to another reader of your pages. I can see that you are keen and must put in a lot of time keeping it updated. THANKS.

All the best for 2001.

Kind regards
Dave. ZS6BNT / G3ZGZ - ham calls

See more of Dave Woodhall's pictures in Gallery 10