Making the most of a rare opportunity. To get the best of the opportunity afforded by a sweep of kites during community KAP walks 2 rigs have been prepared that should run for more than an hour without any need for attention from participants. The initial idea to use Harbord SP rigs still holds for shorter ‘school friendly’ sessions but the most likely kite walk will need an hour, if not 2 if a circular route is approved.
Why a servo rig? There are other methods to achieve a stepped rotation of the camera, clockwork, rubber-band and a pendulum ratchet have all been successfully used. To get extended run time with a constant speed of rotation a ‘360’ servo is a reliable and predictable method. The drawback is the weight of the servo, it’s battery and the need for a controller to drive it. A single 3.7v cell running a ClickPan controller will work for hours. A simple method of suspension is to bolt a Picavet cross onto the servo. This has the entire weight of the camera suspended by a fixing designed to restrain rotation rather than act as a hanger. A camera weight limit of 250g seems reasonable given it takes a great deal more force than that to strip the threads on the bench.
A heavier camera (on the left below) needs more secure suspension than a screw into the servo and this is achieved by using a transfer gear so that the line of force is passed through an axle to the top of the inverted L plate. The Brooxes Better Gear Guide ‘BBGG’ pan gear is perfect for the job, being a flexible and tough design specifically made to fit a ‘standard’ servo.
How heavy? The lighter version (on the right above and left below) weighs 135g empty. Camera options as light as 280g for a CHDK controlled A2300 or 460g with a Lumix LX3/Leica Dlux 4 are possible.
The heavy duty version (which will take an 800g DSLR if it has to) is 610g with the Canon EosM, 695g with the Sony Rx1 (above right) and 190g empty. A great deal of the weight is from the gauge of metal used. 2mm thick aluminium has big advantages, it’s easy to work cold and, once formed, is strong enough to take transport with a camera attached. Kite photography is hard on kit so engineering for robustness is important. It is a sad truth more damage to equipment occurs before it leaves the ground than in the air.
The ‘L’ plate is a flat 25mm strip of aluminium with the servo cut out prepared before it’s bent into shape. Making the bend requires a bit of practice, the idea is to support the work in the vice just below the fold line and push it over in a single continuous move, stopping half way will crack the metal when restarting. Once bent it stays bent, re-bend and its broke. No hammering is needed, lay a rag across the jaws to save scratching the shiny stuff. All the holes are drilled to fit once the servo is fitted. The top of the plate has space for a switch and is offset for the centreline of the servo spindle.
Rotation. The rotation control supplied by Gentles clickPan is widdershins for a good reason. The movement is in the direction of tightening the thread on the spindle not loosening it. In theory the lock nut shouldn’t move but if it did the turning of the servo wouldn’t make a bad situation worse!
Synchronising the pan and shoot. Both clickPan and clickPanPro operate the pan and shutter servos at a fixed interval. Ideally adjusting the interval to allow for the Picavet to settle and AF to work is needed. The more basic clickPan is fed via a variable timer to delay the sequence, it has an interval between 2 and 30 seconds so that the pan move does not overlap with the shot. The pan is complete in 75 seconds and takes 16 shots for the circle. Continuous rotation is possible under clickPanPro control and can be used in conjunction with the RX1 panoramic mode.
Fixings. The 360 servo was supplied pre-modified from a TowerPro MG 995. As luck would have it the servo has a standard M3 machine screw for the crown bolt, this means a longer replacement is easy to find. The longer bolt is a big help to get a good secure fixing for the Picavet. The Picavet is a Brooxes ‘compact’ (available from KAPshop) which is in 2 parts, this is useful as further security was achieved by using a cut down servo horn counter-sunk screwed to the bottom Picavet plate. Bonding the bolt into the servo spindle with LocTite is recommended.
The offset suspension by use of the BBGG assembly requires counter-tightening lock nuts above the driven gear and at the Picavet cross. Fitting of nylon washers and spacers is important as, if the drive nuts turn against the shaft and jam on the BBGG plate, it can lock up:
A little light machine oil helps. The top nut is a ‘nylock’. The drive can be quite loose provided the gears maintain mesh. I used an oversize hole on the L plate for wriggle room on fitting and packed it with a wide nylon/steel/nylon washer sandwich to reduce wear on the L plate.
Balance. The 3 big masses to arrange are battery, camera and servo. Fortunately most compact cameras in portrait aspect have a centre of gravity close to a vertical line passing through the centre of the short side.Getting a perfect fit between the CoG and the centre of rotation may be possible but it’s not a simple thing, given the amount of movement a KAP rig will have I reckon this is close enough.
Power and switch. I have a good collection of mobile ‘phone batteries salvaged from my teenage sons ‘phone abuse period. They are great for powering rigs: light at 24g, high ampage at 1400mA and at over 3.7v they will power pan and shoot servos for hours.
To get them to work I taped a Futaba fly lead to the terminals, I was unable to solder into the battery terminals so contact relies on tape to do the job, a good sized blob of solder on the wire ends does the trick.A switch is not really necessary, a ‘make and break’ connector works well enough but I have found, particularly on light wind days, there can be a lot of waiting followed by sudden, fumbling, starts. The switch saves an awful lot of close up shots of grass and feet as well as ‘is it on?’ panic at the last moment when releasing the kite. I used a parts bin offering, I think it was once part of a radio.
Capture. When the weather gods permit testing the height/ overlap /tilt set-up begins. Consistent light and height are desirable. The speed of the sweep is important too-if it’s too slow the kite will have moved the rig to a new centre before the sweep is complete confusing the fit.
Stitching the panorama. So far I have found portrait shots tend to stitch better than landscape, with luck most of the shots have a clear horizon line across them which saves a lot of effort in the alignment stage. The fewer shots used the better the outcome and the deeper the overlap the more chance of getting sharp shots in the mix.