Guide for building a CHDK Panorama Rig.
CHDK has opened up unlimited possibilities for CHDK compatible cameras. It is remarkable that a group of guys have managed to reverse engineer closed hardware code and enhance the capabilities of point and shoot cameras to rival the capabilities of professional cameras. Guys; keep up the good work.
There are a number of home made panorama rig designs circulating on the net. Most of them have inherited design flaws to be useful or practical for a CHDK based panorama rig.
Building a panorama rig looks simple but in reality it is complex. The hardware requires precision movement to be successful. It is not as easy as gutting a floppy drive for the stepper motor, a hard drive for the bearing assembly movement and gluing a camera mount on the centre. A floppy drive stepper motor has relatively no torque; it is designed to drive a plastic read/write head on guide rails not rotate a heavy camera. Professional panorama rigs use geared stepper motors. They are precision equipment and expensive to buy. By the time you have purchased all the parts to build the rig, it is cheaper to buy a professional ready built rig.
One alternative is to use servo motors. The KAP guys have years of experience in that field. They have perfected the electronics and hardware. It is cheaper to buy a ready made rig and electronics than buy the parts and construct it yourself. There is one disadvantage to using a KAP panorama rig on a tripod mount. A KAP pan/tilt rig is designed to be mounted on a kite with the rigging evenly balanced. It is designed to be flown, then dismantled and cleaned before the next flight.
A redesign of the KAP pan/tilt rig is required for the rig to be suitable for tripod panorama photography. KAP pan gearing is on top of the support rig, using the kite to suspend the rig. A tripod based rig needs to be compact, portable, containing dust free gearing. Most important the gears need to be on the bottom with the geared shaft supported in two places. The modifications can be done but you may have to build a custom tripod or modify and balance the rig weight on an expensive commercial tripod. If you choose to use a KAP rig design, it is best to join a KAP forum and ask for expert advice. The chances are that the components used may be universal and the support bearings available as a kit.
Build your own rig.
With a panorama rig you are only interested in the horizontal aspect. The vertical can be manually adjusted. You do not need a remote control; therefore a geared motor instead of a servo can be used. The cheapest motor on the market is the geared motor assembly salvaged from a cordless drill. The down side is the rotation is too fast for panorama photography. Pulse width modulation chips are readily available. The PWM chip performance surpasses a software programmed microcontroller design. The PWM chip timing is enough to pulse drive the motor, but not long enough to overheat the motor from continuous pulsed use.
For example an S3IS camera using a SanDisk Ultra II card will only shoot photos at 5 second intervals. Any faster, the camera will not respond. A simple way to pan the rig is to use a CHDK USB shutter release cable to shoot; one second later activate a one shot to turn on a 555 timer. The 555 timer switches on the PWM to the motor. You need to allow a two second stabilising time, and then repeat the process. The electronics design aspect is simple; hardware timers chained together without any feedback from the camera.
Dismantling a cordless drill.
Most of the cordless drills are simply held together. Once you unscrew the casing, the motor and battery assembly drops out. Cordless drill chucks are held into place with a screw located inside the chuck. The screw is right hand thread. Open the chuck fully and with a screwdriver turn the screw clockwise to remove it. The chuck is conventional left hand thread. Place the chuck side on a block of wood and hit it with a hammer. You will end up damaging the chuck before you can unscrew it. You will need to buy two nuts and washers for the bracket mount. Keep the screw; you may need it as a locking screw. What you use for a housing and camera mount is dependent on readily available materials. The KAP guys have plenty of photos of camera mounting brackets.
If you have access to the right tools and a drill press, a stepper motor can be used instead of the existing motor. You will need to dismantle the gear box assembly, remove the hammer components and re-grease the gear box. A geared stepper motor will give you a precision stepping rate. You only need a very simple one step function. There are plenty of simple stepper circuits circulating on the net. Use readily available components.
The panorama step/travel distance depends on too many variables to publish a one size fits all circuit. It is purely trial and error. Keep the electronics design as simple as possible. If you are using 555 timer circuits, be aware that the first pulse on power up on common variety 555 is inaccurate. That is an inherited design fault in the 555 chip design. Power up the chip let it stabilise, do not use the power rail to switch the timer on and off.
Barrel distortion photos look horrible. It is best to have many photos with a large overlap than a few photos with a small overlap. Use the CHDK USB cable to trigger the shutter and single step/pulse to your next location. Once you have worked out your step/travel for a given focal distance, you can automate your pan procedure.
Currently I am building two panorama rigs. One using a geared motor with one revolution in 10 seconds; the other a heavy duty geared stepper motor. Once I have perfected the rigs, I will post an updated guide and general purpose reference circuits.
Keep It Simple Stupid.
CHDK enhancements and scripting has made most of the high tech pan designs circulating on the net obsolete.
Google; there are enough simple general purpose circuits that use 555 timers, stepper and PWM circuits. Use circuits with cheap readily available components in your locality; because if your rig breaks down, you do not want to wait months for an exotic component - or - find out that the original hardware designer/developer has disappeared.