BASICS / Cradles /
Rules & Guidelines
The MOST important aspect of building a KAP Camera Cradle is proper balance. Without proper balance the servos will have to strain to move the camera. An out-of-balance camera cradle could also hang from the kite line out of level. Stated once again the Primary Consideration when designing a Camera Cradle is BALANCE!!!
We will show the BALANCE considerations needed to design a Double U ("UU") Cradle with HoVer. Building a HoVer Cradle for your first KAP cradle is not recommended!. A simple "UU" without HoVer follows this same process with the exception of Step 2.
DETERMINE THE CENTER OF GRAVITY (CG) OF THE CAMERA.FIGURE 1 FIGURE 2 The CG is the point where an equal amount of weight exist on each side of the CG point. The CG is fairly easy to determine with Point-and-Shoot cameras because they tend to be rectangular boxes with their weight distributed fairly evenly within their cases. SLR cameras will require some testing.
A simple way to test for a camera's CG is to use a round object such as a pencil. Then place the camera on its back across the pencil (Figure 1). Make sure the camera is loaded with film and batteries. You will not be able to perfectly balance the camera but you will be able to determine the balance point within a 1/16" to 1/8" (1.5mm to 3mm). Now rotate the camera 90 degrees, with it still on its back, and measure the balance point on this axis (Figure 2). The third axis balance point can be estimated for a P&S camera to be midway between the front and back of the camera (Figure 3). A SLR camera will need to be measured on all three axes. The intersection of all three of these lines of balance is the CG point.
DESIGN THE HOVE BRACKET.
The HoVer bracket is usually an "L-shaped" bracket. The bottom part of the "L" will hold the camera. It must be wide enough for the camera to rest on. It must also be deep enough to support the camera and allow for a 1/4 inch hole to match the location of the tripod mount on the bottom of the camera (Figure 3). Leave clearance between the back of the camera and the upright portion of the HoVer Bracket to allow for the attachment of the HoVer axle hardware. If there are controls on the back of the camera that may need access, then provide cut-outs or space to reach them.
(Skip this step if you are NOT using HoVer on your Camera Cradle.)
(Red = HoVer Bracket) On the upright part of the HoVer bracket the axle of rotation must attach at the CG point as seen from the front of the camera (Figure 4). The shutter servo is usually mounted to the HoVer bracket (notch at top of HoVer bracket). The CG determined in step one may no longer be accurate. The weight of the bracket itself will change the CG and if a servo is attached to the bracket then this too can change the CG point. Once the bracket is assembled with the camera and any servos attached, recalculate the CG. At this new CG point attach the HoVer axle to the back of the HoVer bracket.
DESIGN THE TILT BRACKET
The Tilt Bracket is the lower "U" of the Double-U design. If you are not designing a HoVer Cradle then the Tilt Bracket will be the first part you will make. The first critical measurement for the Tilt Bracket is the length.
On a Non-HoVer Cradle the camera will rest on top of the Tilt Bracket (Figure 5). The length of the bottom portion of the bracket should allow for clearance on each side of the camera for the Tilt Axle hardware. Some cameras with electronic shutter release have their connectors on the side. Be sure that you leave enough clearance for the connectors. Don't worry if you have to mount the camera slightly off-center on the Tilt bracket to provide clearance for your camera, this will be taken care of on the upper "U" bracket.
The length of the Tilt bracket for a HoVer rig needs to take into consideration the clearance necessary to allow the camera to rotate from Horizontal to Vertical (Figure 4).
The two legs of the Tilt bracket should be long enough to come past the axis of Tilt that passes through the CG of the camera. Don't forget that the bracket itself, the shutter servo, and the HoVer servo can alter the location of this point. You should check the Tilt CG with the camera and all servos attached to the Tilt bracket.
The increased complexity of balancing a HoVer rig is one of the primary reasons that HoVer is not recommended for the beginner.
DESIGN THE PAN BRACKET
The Pan bracket horizontal length will depend on the hardware that you chose to attach the Tilt bracket to the Pan bracket. Once you have determined how much clearance you need for the Tilt axis hardware you can now measure the length needed for the horizontal length of the Pan bracket. The length needed for the vertical legs of the Pan bracket will depend on how much clearance is needed for the shutter servo or in the case of the HoVer rig clearance for rotation of the camera format (Figure 4). Be sure to take into consideration clearance of any components that you plan on mounting underneath the horizontal section of the Pan bracket.
Next the balance point along the horizontal section of the Pan bracket must be found (Figure 6). Be sure to attach all hardware, servos, switches, receivers, and batteries where you intend them to be located. Using you finger you should easily find the point to attach the Pan axis. The camera cradle will hang from the picavet or pendulum at this point as well as Pan about this axis. If you get the balance off at this step the entire cradle will hang at an angle.