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
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
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
■ FIGURE 2. The Styrofoam measures 5-1/4
inches across and the plywood six inches
■ 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
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
The yaw servo
attaches to the quad
panel with a shaped
Styrofoam block. The top
and bottom face of the
block is covered in thin
plywood for strength.
January 2006 85