Blow-back and pre-angle

The picavet system does a good job of keeping the camera level, except for light rigs in strong wind. Light rigs can suffer from blow-back where the wind blows the rig back away from the vertical.

You can see how the camera is angled compared to the horizon in the left photo, which would result in many unusable tilted shots. The effect is greater up higher in strong wind and when the camera is side-on.

The right photo shows the camera pre-angled to counteract the blow-back effect resulting in a higher number of level shots.

This is only possible with a rig that allows the camera to rotate from landscape to portrait orientation.

400g Aurico pan rig in Bft 5 (18kn). 

The picavet cross on my basic GoPro rig has extra mount hole positions allowing the camera to be mounted off centre for the same reason.

Black Lighthouse and Fort Queenscliff

Line-pull ratios

After recording line-pull with 4 KAP kites in Bft 1 to 5 (2 to 18kn) I have worked out a rough estimate of line-pull ratios. The ratios are expressed as line-pull (lb) to wind strength (kn)

Line-pull Ratios (lb:kn)
7ft Pirate Rok              1:1
ITW Levitation Delta    1:2
Peter Lynn 2m2 Pilot   2:5
PFK Nighthawk            1:3

Which means the line-pull (in pounds) of the Rok roughly equals the wind strength (in knots). The Levi delta pulls half as much as the Rok and the PFK one third as much.

For example: In 12kn the Rok pulls at 12lb, the Levi pulls at 6lb, the PL pilot pulls at 5lb and the PFK pulls at 4lb. 

Rok and PFK in Bft 1-2. Insufficient wind for the Levi delta and PL 2m2 Pilot.

Four kites in Bft 3 

Line-pull measurements

The amount of pull on the line dictates which KAP rig can be used. I have started recording line-pull using an electronic luggage scale ($9 on ebay) to help with kite selection.

I have found that line-pull of about 3 times the rig weight is enough to safely lift the rig. So I need 7lb pull to lift my 1.1kg SLR rig. (Apologies for the mixed units, must start measuring pull in kg!)

Here is a clever interactive lift/pull calculator from Kaper e-zine. Plug in rig weights and see line pull and angles.

Of course line angle also matters. Deltas can fly almost directly overhead. At times the delta and rig can be in perfect balance leaving next to no tension on the line in your hand and zero movement of the rig. Perfect for sharp KAP shots. It's a magical moment, hard to believe it's possible.

My intention is to build up data for each kite in a range of wind strengths.
It's early days but it seems with the 7ft Rokkaku line-pull in pounds is pretty close to wind strength in knots. For example I would expect line-pull of 7lb in a 7kn breeze.

Here are two video compilations of kites compared in Bft 4 and Bft 2.
I'll do Bft 3 and Bft 5 when the conditions permit. I have tried Bft 1-2 but the Rok was the only kite capable of staying up.

Three kites compared in Bft 2

Four kites compared in Bft 4

Eventually I'll put together videos and publish a line-pull table for each kite separately in the full range of wind strengths.

Beaufort Wind Scale
Bft 1     1-2kn          Calm - Not enough to fly. Go diving
Bft 2     3-6kn          Light breeze - Rok will fly, others maybe.
Bft 3     7-10kn        Nice breeze - All kites will fly. Need to match kite to rig.
Bft 4     11-15kn      Decent breeze - All kites will lift rigs easily. Upper range for the Rok.
Bft 5     16-20kn      Strong wind - Too much for the Rok and Levi
Bft 6     21-26kn      Howling - Only the PFK will survive.

Pirate Rokkaku

A new kite, very exciting.

Size comparison: PFK Nighthawk        9ft Levitation Delta                      7ft Pirate Rok

The rok almost didn't get delivered due to a couple of crucial typos in the shipping address. Luckily I knew in advance and retrieved it from the post office before it was returned to the sender.

This is a 7ft rokkaku made by SkyDog Kites and sold by Picture Pretty Kites. Cost US$99 with $40 delivery. I would have preferred a single colour kite but there wasn't much choice for this size and price.

First flight of the Pirate Rok in about 6kn

It is very well made from good quality ripstop and has fibreglass spars. More expensive roks have carbon fibre spars and so are a little lighter and stiffer. Fibreglass spars may extend the upper wind range being more flexible.

I'm hoping this kite will have more lifting power than my Levitation and PFK deltas and will lift the D80 in lighter winds.

First flight was in perfect light breeze and it behaved beautifully with very little movement. Line pull was 2 to 4lb and lifted the 300g Canon S100 manual rig with ease.

Tensioning of the upper and lower spars tunes the flight characteristics. In the video I tried 10" of curve in the lower and 8" in the upper, which is a good starting point. Flattening out the curves produced more side to side swaying.

KAP extra bits

These are the peripherals I regularly use to make serious kite flying safer, easier and more enjoyable.

1. Leather gloves for the dominant hand with pointer finger and thumb tips cut off.
The kites we use produce strong pull on the line. With that comes the very real risk of cuts and burns from fast moving line. Gloves are essential, no question.

2. Lanyards for the camera and mounting bolt.
I connect the camera tether to the picavet lines, that way if any part of the rig fails the camera won't plummet to earth but dangle from the lines. A forgotten mounting bolt would be the most common reason for an unsuccessful KAP outing.

3. Carabiner to store the picavet lines.
These line hooks are like grappling anchors and with the picavet lines will very easily twist and tangle. The picavet lines are wrapped in a figure of eight around the picavet cross after connecting the line hooks as shown.

4. Luggage scale with gamma hook to measure line pull.
This gives me an idea of which camera rig is suitable for the kite and wind strength.

5. Big carabiner to walk the kite down.
Sometimes when there is enough space you can walk the kite down by clipping this big carabiner to the kite line and walking towards the kite.

6. Kite cleat for securing the kite line when using the skate wheel reel.
Also called a Henry's handle I think. A few figure of eight wraps of line around the cleat will hold the kite. I can either clip the kite cleat to my backpack, which I always wear, or to a tree or post using the longer loop.

7. Longer loop of rope with carabiner to tie off the kite cleat or strato spools.
This is long enough to wrap round something solid like a tree, rock or car tow ball.

8. Website card.
Because people will be drawn to you while flying big kites with "what is that" dangling from the line, and it's good to be able to direct them to your website to share the results.

Nikon D80 AuRiCo rig

Once I knew my kites could lift the SLR it was time to add some AuRiCo.

This rig was to be another limited pan, manual tilt style, which involved some very simple shed tinkering.

Just had to bend up some aluminium as a pan bolt bracket and rivet it on to the top U. This bracket steadies the pan bolt which is no longer solidly fixed to the top U but rotates.

The bracket also acts as the pan servo mount so I had to think about how far away from the pan bolt the servo needed to be positioned. That distance depends on the thickness of the servo and which gear cogs are used.

Nikon D80 SLR AuRiCo autoKAP rig - 1195g

To keep the rig as simple and light as possible I used velcro and rubber bands to hold the AuRiCo and batteries on.

As the pan servo is only rotating the rig it doesn't need to be too big or securely bolted on. I started with a Futaba S3003 but ended up using Turnigy 380MG stuck on with double sided tape and cable ties. Although the servo is moving over 1kg of camera and rig there is a lot of give in the picavet suspension setup.

You can see in this video how the load transfer from servo to rig is quite spongey which reduces strain on the servo. The servo moves the picavet on its lines first then the rig swings around.

Nikon D80 KAP shots

Nikon D80 SLR manual rig

I recently upgraded to a Nikon D7000 for underwater photography so my original SLR, a Nikon D80, doesn't get much use these days. To reward the D80 for reliable long service and paying for itself many times over I thought it might like to go flying.

It's not the ideal KAP camera being quite heavy (672g body + 202g 18-55mm lens = 874g all up)
and it doesn't have an intervalometer but that didn't stop me. James Gentles makes a lovely little device called GentLED-AUTO which is an IR remote intervalometer weighing just 20g. I just happened to have one sitting around so it was time to give SLR KAP a try.

First step was to make a basic manual rig just to see if my kites could lift it.
I bent up some aluminium to make a rig similar to the vertical style Aurico autoKAP rig for the Canon S100. But this design, a single vertical support with an L bracket to mount the camera, was way too flexible for the heavier SLR. The spring like flexing would have had the camera bouncing up and down continuously.

Nikon D80 manual rig - 1090g

So I had to revert to the tried and tested double U style. This allows a light and stiff rig to be built using the minimum of material, but it means I needed to balance the camera in the bottom tray carefully following James Gentles guide, which I find much trickier than building the vertical style rig.

The bottom U tray needs to be wide enough, front to back, to accommodate the camera mounting bolt and the pivot holes on each side which are at the centre of gravity for the camera. With this camera/lens combo the centre of gravity is 24mm forward of the camera mount hole. The bottom U needed to be 40mm wide. The top U only needed to be 30mm wide to be stiff enough.




Amazingly the wind was perfect for a test fly on the day I made this rig. Sunny with a smooth onshore 12kn and the Levitation Delta had no problem lifting it all as shown in this video.

I was really pleased with the image quality compared to the Canon S100 partly because the heavier rig isn't blown around by the wind as much.

I have begun to realise that lighter rigs suffer from blow back resulting in angled horizons or more/less tilt than expected. I'll talk more about blow back soon.

Here are KAP shots using the D80

RC Transmitter mod

I mentioned in a previous post, Proportional pan servo, about changing the transmitter control sticks for dial pots or variable resistors.

That meant I could set up the rig so the camera orientation directly related to the position of the pan and tilt controls. You always know where the camera is pointing by looking at the dials.











This video shows how it was done.

It was surprisingly easy with all the components unplugging and plugging back in. I just needed to cut the plugs off unused levers to reuse on the pots. This RC set is 4ch and I only needed 2ch.

I first measured the resistance of the lever pots and got values ranging from 1k to 2k. Folks on the KAP Forum had used 5k successfully so I bought 5k and 1k. Both worked and gave the same range of servo movement.





I got sick of trying to juggle the reel and transmitter at the same time so decided it would be better to move the control knobs off the transmitter to a hand held extension cord. Now the transmitter stays in my pack and the controls dangle over my shoulder within easy reach.

This was easy, really just adding longer wires to the pots.

Lines, knots and reels

Lines
Braided dacron seems to be the most popular line used by KAPers because it gives a good balance between cost, strength and handling.

Drag and weight of the line up in the air are very important considerations. Thinner and lighter line will allow the kite to fly higher. High tech materials like Spectra and Kevlar are thinner and lighter for a given strength but need more careful handling and cost more than dacron.

I have 3 weights of Ashaway dacron bought from from Into the Wind in the US: 100lb for light wind, 150lb for general use and 200lb for strong wind. Haven't found a supplier in Australia for bulk line. Lengths are 500ft and 1000ft, but have never let out the full 1000ft.

I often measure the pull on the line with a small electronic luggage scale. Anything over 15lb pull feels scary and my heaviest rig weighing 1220g (2.7lb) only needs 7lb of pull to fly safely. So in theory even 100lb line is strong enough and it would wrench out of my grasp before breaking.

Knots
Any knot will reduce the breaking strength of a line, some by as much as 50%, so knot selection is very important.

The All About Knots blog explains the causes in depth. Turns out it's the radius of the first turn in the knot. A tight radius places more strain on the outer fibres in the line and they break first. Knots which reduce that first radius or bury it within the body of the knot spread the strain more evenly across the fibres and so are stronger.

A blood knot or fisherman's knot is one of the best, retaining up to 90% of the line strength, so that's what I use in critical situations.





Reels
We all start kite flying with a simple hoop or halo reel but that quickly becomes difficult with bigger kites. I now have a range of winding reels for different wind strengths. Some folks say you should always walk the kite down and never wind in under tension. That doesn't work for me. Maybe it's my location and style of KAP but I'm forever winding in, tweaking camera orientation, letting out again and rarely have enough space to walk the kite down.

Strato spool
This is the heavy duty reel for strong winds (16kn+ or Bft 5+). It features a solid timber core, bracing bar with line guide and an extended winding handle for extra leverage.

The classic strato spool also has a brake bar that slows the reel with friction when squeezed against the bracing bar. For a simpler build I left the brake bar off and use a gloved hand for braking. That works fine for me.

This reel is a tricky build because you need to make the solid core. I used a jigsaw to cut out  3 125mm diam circles from pine floorboards, smoothed them off as close to circular as I could then glued them together with epoxy resulting in 63mm thickness. The sides are 6mm ply with another 6mm section along the axis of the handles, glued and screwed to the core. Diameter 190mm with the handle extending a further 100mm out. I used skate bearings on an 8mm bolt for the axle. The bracing bar is 19x 45mm hardwood.

Here are the plans I initially followed for the strato spool. I made changes to the design when I found it couldn't hold 500ft of 200lb line and I didn't like the eyebolt style line guide. A T shaped top section with line guide just narrower than the reel width is essential in my opinion.

Jim Powers, who has built and destroyed many strato spools, shows how to use one in this video.

Skate-wheel reel
This is a very simple but smooth reel for lighter winds (up to 12kn or less than Bft 4) with a fast winding action. A rollerblade wheel forms the centre handle. It is difficult to hold steady for winding when the wind is above about 12kn but is a delight to use in lighter winds. The core is formed by 8 or more 60mm x 3/16th bolts. The sides are 6mm ply held apart by aluminium tubes on each bolt. Overall diameter is 260mm with a 150mm cutout.
Eric Kieboom's version is much nicer than mine.

Hybrid strato spool
This is my favourite reel, used for most of my kite flying. It combines the steadyness and power from the bracing bar with the smoothness and fast winding of the skate-wheel reel. I would change to the strato spool in more than 15kn. The sides are made from nylon chopping boards and the bracing bar is shorter than usual. Diameter 250mm, 60mm core bolts.

SDM - Stereo Data Maker

SDM is a version of CHDK (Canon Hackers Development Kit) designed specifically for syncing 2 or more Canon compact cameras for 3D photography. It also simplifies CHDK for single cameras and Kite Aerial Photography.

In a nutshell, it means a lot of the irrelevant CHDK stuff is gone leaving a much cleaner menu.

Just like CHDK you need to establish your firmware version, download the correct build, copy it onto a freshly formatted SD card, lock the card and you're in business.

Development of SDM seems to lag behind CHDK, probably because developers like David Sykes, another very clever KAPer - see this KAP forum post, need to get a hold of two identical cameras to test syncing function. It's not officially available for the Canon S100 yet but beta versions are easily obtainable. Ask nicely on the KAP forum.

Dave Mitchell's ACID and SDMinst apps are very helpful once again to get it all running.
UPDATE: and his new STICK and ASSIST apps are even easier to use.

The value of SDM and CHDK is the ability to run scripts. These are simple programs written in uBasic language. There are plenty of scripts pre-loaded with CHDK/SDM or you can download more from the KAP forum or CHDK/SDM websites.

uBasic is a very simple and easy to read language that can be edited in any text editing app like Notepad or TextEdit. I used TextWrangler on the Mac. The scripts must be saved as simple text files with the file extension .bas

WindWatcher and HQasem have shared some fancy scripts on the KAP forum.

My basic intervalometer script looks like this:
@title APN intervalometer
@param t interval(sec)
@default t 5

rem single camera, display off
sleep_for 1000
sync_off
turn_backlight_off
sleep_for 1000

rem endless loop with delay
while 1
shoot
sleep_for_seconds t
wend
end

If you want to use it copy the text, paste it into a text editor then save it as APNintvl.bas or whatever you want. Feel free to edit and personalise it to your own needs.

Copy the .bas file into the SCRIPT folder in the CHDK folder on your SD card and it will appear as a choice in the list of scripts.

Here's how SDM appears on the Canon S100 screen:

 Splash screen on startup. Wait for it to go before pushing any buttons.

 Push the Review or Play button to enter <ALT> mode. 

Currently selected script (APN intervalometer) is displayed along the bottom left.

 In <ALT> mode push MENU to bring up the SDM Basic menu

 Here's the Scripting screen where you can load a different script or change current script parameters

This is my intervalometer script set to shoot every 5 seconds. This script also blanks the screen while shooting which prolongs battery life.

KAP rigs - autoKAP

AutoKAP rigs move in a pre-programmed way without any input from the kite flyer. Unlike the RC rig you can fly the kite and just let the autoKAP unit control the camera movements.

There are a few autoKAP electronic modules available but I use AuRiCo (Automatic Rig Control) by Peter Engels, another clever KAP electronics inventor. Using 10 dip switches you can pre-program tilt, pan, shutter function (and CHDK USB input) The AuRiCo unit replaces the RC receiver.

In normal use you would need a continuous pan servo, a normal tilt servo and maybe a shutter servo (if you don't have an intervalometer) You can select the time of pan rotation (0.2 to 1.3 sec. Your gearing then determines the angle of panning) and the interval between movements (5 to 240 sec) and the number of tilt movements (0 to 4 tilts from 0º to 70º down)

So you could set the rig to - shoot, tilt down to 15º, shoot, tilt down to 45º, shoot, tilt down to 70º, shoot, pan for 0.4sec and tilt back up to 0º and keep repeating. This covers all angles but most of the time I like to target a specific view.

Canon S100 AuRiCo pan rig - 400g

So the way I use it is to plug an un-altered pan servo into the tilt socket giving me a 4 shot repeating pan. With 4:3 gearing the rig pans through 90º.

The chassis in this photo is 25mm x 1.6mm aluminium. I have since changed to 20mm al and done away with the AuRiCo case to bring the weight down to 400g.

I have found with my manual rig that aiming can be off and I often miss the target.

This panning rig gives me a much greater chance of capturing the intended target and allows the possibility of panoramas.