A rig for Tim

Tim Carter, an archaeologist working in Suffolk, got in touch and asked about KAP for site recording. After a couple of flights he has arrived at the conclusion this is an aerial platform with potential.

Gt Finboro Church by TimAfter just 2 flights, flying blind with help from the KAP forum Tim achieved this creditable shot of Phipson’s  spire at Gt Finborough. The exposure is less than perfect but the positioning is spot on.

We got a gap in the weather and I invited him over to Blake towers and get a training session in despite the beefy wind. We have had days of overcast so the sight of the Sun forced my hand. I find teaching KAP very difficult as there is much discussion to be had on equipment and it’s difficult to get across just what the strengths and weaknesses are unless you get out and fly, KAP after-all is a practical skill.

To begin we went over some recent photogrammetric capture and discussed how effective KAP is compared to other methods. We return to the problems of reliability, risk, permission and the relative value of the drone.

Exploring the kit. There is a difference between what you can learn from the web and what you can learn from life, my kit has been lugged around and flown for hours, all the  bits that can be broken have been, for a beginner getting your hands on what works can save a fortune on experimenting with things that don’t. Unexpected gaps in understanding appeared: I was surprised Tim’s pivot was jammed solid- why?   It turns out you can’t tell from a still photo how a moving part works.

Economy of cover: fixed nadir or directed camera? The difference between AutoKAP and directed camera work might seem obvious but with mapping cover the  value of oblique shots should not be overlooked. On a site where you can’t get all the way over it a ‘straight down’ rig will limit capture. Fixed nadir has been very successful in open upland spaces where you can get access to adjoining fields but when movement of the kite is restricted  by trees, boundary fences, overhead lines etc. getting obliques makes all the difference, and oblique shots are best taken with a directed camera.

PS modelIf you can’t move far enough upwind the kite will be stuck over one edge of the site: obliques are required to achieve cover.

Cost and benefit of video relay. Video relay from a kite suspended camera is a boon but it comes at a price. A light wind KAP scenario might well end up with the camera 300m or more down wind of the operator but only achieving 60m in height, the video link needs to be of sufficient quality to cover the range at a low voltage for an extended duration. And that means quality kit. The FPV model aircraft community have solved this but the lightweight low power gear is expensive. A good transmitter will set you back £80 or so and a receiver, screen and tuned antenna set (at least) a further £50. If your budget has been dented by £100 for a camera, £100 for a professional kite and £50 for line the additional cost of  video feedback can look a step too far. Much can be done without video relay and the skill of estimating camera position by eye is well worth honing. To see the value of it we flew a directed camera in Bft 5,Wind 02012015

A practice flight. 1st we launched the PFK, it took off like a rocket and settled down to a savage, tugging series of sweeps across the wind window, the sort of thing it does a lot and I’m confident it won’t invert but the insistent tugging on the line was bad news. I wanted a softer ride for the camera so decided to risk the Levitation, a short flight might be possible with the big 8mm carbon spar and so it proved to be. The delta was being pushed  around the sky in gust but the line was steady and the carbon wing spars flexed properly to keep the nose of the kite into the wind. The camera was launched and flew off down wind with the line racing after it.

_DSC1174

Tim was able to shoot as the line was paid out, proving the value of slack line. As the kite gained hight I began to realise the strength of the wind and began to haul down less than 5 mins after hitching the rig to the line. The kite was spending too much time pushed to the edge of the wind window to leave it up there long. Gusts up to 30mph usually keep me indoors but even a short experience of flying the directed camera is better than none.

_DSC1183

_DSC1193a handful of shots later and the camera was recovered well before the delta landed in an unpleasant dive. Bft 5 is not a happy place for KAP but the launch- settle-wait- hitch-rise & fly-haul down-recover  procedure kept the camera safe.

Fowform vs Delta. The wind eased in the afternoon and we were able to fly the Didak Explorer 2.7 and the Levi back to back. This is instructive as the awkwardness of the flowform at launch was evident as was its greater power over the delta.

  • Delta= quick and easy with a steep angle
  • Flowform = tricky launch, low angle and lifts a bigger payload.

As night fell we flew the Levi with an autoKAP rig taking progressively blurrier shots of the common before we reeled it in. By the close of play Tim had flown 3 of the best kites for the job in fairly tough conditions and got some practice with RC control with video relay. Not a bad days work.

An autoKAP rig is a good backup for context shots and a safe option when the wind is light or when safety directs. I have been tinkering with a custom rig for the S95 and Tim asked if I’d build one for his (almost identical) S100.

Tim threw a spanner in the works by asking for landscape aspect so these are the assembled parts prior to figuring out how to cut the frame pieces:

Tims rig Parts assembllist-1The frame needs to accommodate the USB connector for shutter control so I used a wide tilt plate to allow space for the connector and the fingers needed to fit it:

S95 rig build 1I’m hoping for a robust compact build, it’s taking shape.

B

About billboyheritagesurvey

Heritage worker
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