KAP FPV

What do you do when you're busting to try some FPV gear and it's too windy for the RC plane?

Lift it with a kite. 

For ages I have been jealous of KAP buddies Ramon Pallares and Tom Benedict with their video downlinked KAP rigs. Finally I have the equipment to try it myself.

The trigger for this was Hobby King's release of the $30 Quanam FPV goggles. They include an LCD  that doesn't go to blue screen when the signal drops out.

The video link uses a Boscam 5.8GHz 200mW video transmitter and receiver, also from Hobby King.

Pan servo operates via one of the pots on a 2.4GHz Turnigy 9X.

The day was cold, wet and blustery but the PFK Nighthawk delta handled it easily and let me capture this jiggly footage. With FPV you can actually see what the camera is pointing at, very satisfying.

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.

KAP rigs - RC Canon S100

The Lumix LX3, a superior compact camera, was soon to be reclaimed by it's rightful owner (wife) so it was time to find a replacement.

Using the camera feature search on DPReview I looked for any compacts with 24mm wide zoom and intervalometer to replace the shutter servo. The only camera currently available fitting the search was the Lumix LX7 weighing 298g, a little too heavy for light weight KAP.

An alternative option was to add intervalometer function to a Canon compact using the CHDK firmware hack. The Canon S100 looked interesting, with GPS, only weighing 190g and A$100 less than the Lumix.

DWI  had the S100 for A$280 which was fine by me. I tend to think of KAP cameras, like underwater cameras, as expensive disposables.

Canon Powershot S100 RC rig - 460g

I am finally happy with this setup.
- CHDK/SDM intervalometer (explanation coming soon)
- Proportional pan and tilt using Turnigy 380MG mini servos
- Brooxes compact picavet and tripod bolt from the KAP shop
- Fibreglass face plant protection bar
- Safety leashes on the camera and tripod bolt

Proportional pan servo

A more logical method for pan is to use a larger gear on an unaltered servo with a smaller gear on the pan bolt. With the correct ratio (5:2 in my case) you can achieve +/- 180º rotation (=360º)  from a +/- 45º servo.

Also by changing the transmitter pan lever for a rotating pot or variable resistor (more about that later) you can make the rig pan position match the transmitter pan knob position.

This means you always know which direction the camera is pointing by looking at the transmitter pan knob.

A note of caution. Small movements of the pan knob give large movements of the rig. You need to be prepared for a sudden rotation of the rig when it is turned on. It's a good idea to turn it on to align the rig before hanging from the kite line and with no tension on the picavet. This way the picavet will spin on start up rather than the rig.

Continuous rotation pan-servo hack

The ratchet pan system needed constant adjustment to keep operating so I decided to change to a continuous rotation pan servo with gearing.

Servos are designed to rotate +/- 30º to 45º but with a simple hack they can be made to rotate in either direction continuously. All that's required is to open the servo, cut out a couple of little plastic tags and drill out the inside of the lower part of the spline. Here's a full explanation of the hack from the KAPER e-magazine.

Gearing down is a good idea to reduce the speed of panning, so a large gear on the pan bolt is meshed with a smaller gear on the servo. This rig used 2:1 ratio but 4:1 is recommended.

One issue you may need to deal with is servo creep. Some continuous rotation servos will not stay stopped no matter how much you adjust the trim switches. James Gentles makes an antiCREEP unit that solves the issue for standard servos. It gives a wider "no movement" zone and slower rotation overall. Unfortunately I found the hacked Turnigy servos did not work well with antiCREEP. The "no movement" zone became too wide.

This three legged rig with continuous pan micro servo and standard tilt servo weighed 560g all up, but suffered from pan servo creep.

Another issue with continuous pan is that you can easily lose track of which way the camera is pointing unless you use a video downlink (extra weight and expense) or some sort of pointer on the rig that is visible from the ground.

Jittering tilt servo

In the never ending quest for a lighter rig I tried some metal geared micro servos. The tilt servo directly supports the camera so it needs a strong metal spline.

This first servo I tried was a Turnigy TGY 113MG servo weighing 12g (a Futaba S3003 weighs 36g) and has metal gears and spline. Torque rated at 1.8kg/cm.

Unfortunately it was not strong enough to tilt 270g of camera, cradle and shutter servo without breaking into crazy jittering, shown in this video.

Even making sure the camera and tray were accurately balanced didn't improve the jittering.

I needed to find a light mini servo with more torque.

The Turnigy 380MG mini servo, 16g weight and 3.5kg/cm torque turned out to be the answer. It has a funky see through purple casing, standard Futaba sized spline with 3mm thread and no jittering.

KAP rigs - RC Carbon fibre tube

The Flickr KAP gear group is a fantastic resource for researching rig designs. There are many different styles of backyard and commercially made rigs but the one that really caught my eye was this one by Eric Kieboom.
Made for the Lumix LX3 using 4mm carbon fibre tube and various aluminium profiles it weighs almost 300g lighter than my first effort. As soon as I saw it I decided to ditch the heavy al rig and use carbon fibre tube. Back to the shed.

Lumix LX3 Carbon fibre tube RC rig - 600g

Here is my first version. The biggest challenge was finding the small aluminium extrusions. The square profile used on Erics corners and pan bolt support was not available in Australia. So I used 10mm tube which made accurate parallel drilling very difficult. Carbon fibre tube is available from Carbon Fiber Australia through their online store. 4mm x 1m tube A$5.95 each plus A$10.45 post.

Eric used CA glue (superglue) but I had some problems getting good adhesion so changed to epoxy.

I also bought a 4ch 2.7GHz radio from Hobbyking.com for A$28 (it works perfectly!) and added a mini servo for the shutter. The plastic mount for the shutter servo slots into the camera hotshoe and flexes when the servo pushes down. This prevents over stressing the servo.

This video shows it in action.

All up weight now 600g with 4 x AAA batteries. More weight could be saved by using mini servos.

KAP rigs - RC 3mm aluminium

At the other end of the complexity range is the full radio controlled rig which is heavier than a manual rig because servos, receiver and batteries are included.

Panasonic Lumix LX3 Aluminium RC Rig - 745g

This was my first RC rig, made from 3mm x 35mm aluminium resulting in a flying weight of 745g. (Flying weight includes everything hanging from the kite line)

The LX3 does not have an intervalometer or IR remote so the only way to shoot is by pushing the shutter button.
My existing Futaba radio was only 2 channel but I needed tilt, pan and shutter control. I devised this system using one servo for two controls, down to move the pan ratchet and up to shoot, with the other channel for tilt. I used standard Futaba S3003 servos and 4 x AA batteries resulting in a rig that worked but was way heavier than it needed to be.

A stiff breeze was required to lift the rig with  constant tweaking to keep the pan/shutter link working.

Building this rig was a good learning experience. The first lesson learned was that 3mm Al is way too thick. 1.6mm would be plenty strong enough.

Soon after completion I saw a carbon fibre tube rig and decided that was what I had to build next.