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.