Nuts & Volts - January 2006

insulation. I cut Styrofoam panels with an Exacto knife and hot-glue them into a box. The box becomes an airframe after it’s covered in multi-layer insulation and a fabric jacket. Three sides of the airframe have square openings where experiments are mounted. The openings are all the same size (a standard for my near space program) and are called access ports.

An experiment is bolted to an access port with a quad panel. A quad panel is a 3/4 inch thick Styrofoam square epoxied to a 1/8 inch thick plywood square plate. The Styrofoam square measures 5-1/4 inch on a side and fits snuggly into a access port. The plywood square measures six inches across. While an experiment is permanently attached to a quad panel, the quad panels can be moved to any of the access ports in the airframe. In addition, since every one of my airframes has same size access ports cut into it, I can also move experiments between airframes.

A quad panel bolts to an access port with four bolts. The bolts pass through the inside corners of the Styrofoam square and to a thin plastic plate interior to the airframe. The quad panel remains on the airframe because the sides of the airframe are sandwiched between the quad panel and the interior plastic plate.

Using quad panels makes reconfiguring a near spacecraft a breeze. This brief description should be enough for you to construct a quad panel.

■ FIGURE 2. The Styrofoam measures 5-1/4 inches across and the plywood six inches across.

■ FIGURE 1. The access ports on this airframe measure 5-1/4 inches SQUARE.

The reinforced block is epoxied to the plywood face of the quad port. The servo slides into its pocket in the block and is held in place with two bolts. Figure 4 shows a diagram of the block I designed.

Now that the yaw servo is attached to the quad panel, we can attach the rest of the arm mechanism. The next piece is the rotation base. The rotation base holds the pitch servo, which raises and lowers ( pitch-es) the arm. The rotation base is

■ FIGURE 3. An x-ray view of how a quad panel bolts to an access port.

MAKING THE BIOCA

The BioCA is mounted to a quad panel just like any other experiment. The BioCA uses two standard 42 inch-ounce servos and one micro-servo to move its CCD camera around. The first servo is the yaw servo and it rotates the arm’s base to the left and right. The second servo is the pitch servo and it raises and lowers the arm. The final servo is a micro-servo and it’s the CCD

camera’s pitch servo. It rotates the CCD imager left and right so it can view objects just beyond the BioCA’s range.

To reduce the workload on the flight computer, a Scott Edwards SSC II controls the three servos in the arm. With the SSC-II, the flight computer can control the BioCA through a single I/O connection.

The weight of the camera combined with its distance from the servos places some torque on the servos. To keep the torque at a minimum and to reduce the drain on the battery, the rest of the arm is built to be lightweight. A large portion of the torque is counteracted with a rubber band. As you will see, the arm is constructed from Styrofoam for lightness and thin plywood for strength.

The quad panel is the first item to build. Cut a 5-1/4 inch by 5-1/4 inch square of 3/4 inch thick

Styrofoam and a 6 x 6 inch square of 1/8 inch thick model plywood.

Center and epoxy the Styrofoam to the plywood. Drill four 1/8 inch holes through the plywood at the corners of the Styrofoam. The Styrofoam side of the quad panel is the interior face and the plywood side is the side with the arm.