This chapter is based on an actual application of an electronics bay in a 7.67" Terrier booster from my 2/5 scale Terrier Sandhawk. The bay is located between the upper and middle motor mount tube centering rings. This is an ideal location for single stage deployment and/or outboard motor ignition hardware placement. Carefully layout your wiring diagram before you begin construction -- it will help you make changes before the final process is over.

Photo 1: Bay Layout and Access

In the photo above, you will notice several things:

"...rounded hatch corners, being the detail freak that I am."

• The switches marked Item "1" are the power and firing circuit shunt for the Adept ALTS2-50K altimeter.
• The switches marked Item "2" are the power and firing circuit shunt for the Adept PST-941 timer.
• Item "3" shows the coupler tubing "lip".
• Item "4" is the connection for the altimeter firing circuit shunt.
• Item "5" is pointing out the recessed T-nuts used to attach the hatch cover.
• Item "6" points to the timer wiring harness which controls power and firing circuit.
• Item "7" points out my rounded hatch corners, being the detail freak that I am.
• Not seen is the connector for the altimeter power switch.
• Physical placement of the mounting plate on the motor mount tube can be seen with the two attachment T-nuts as well.

I seal the edges of the cut-out from the coupler piece along with the body tube cut-out with thin CA., as well as the cut out holes in the flange and body tube. I then sand the edges smooth and uniform, being careful not to remove too much material. I then epoxy the coupler cut-out to the body tube cut-out as shown above in Item "1", centering it in the assembly.

Item "2" points out the 1/4" altimeter vent port. Item "3" points out the access hatch attachment holes. After the hatch cover epoxy has cured, I position the hatch cover in the coupler tube "lip" flange cut-out and drill the 4 holes pointed out in Item "3".

Then I attach the hatch cover to the flange with four #6 Allen head machine screws and T-nuts. Then, carefully placing epoxy around the perimeter of the T-nut body, being careful not to get it on the threads or the adjoining hatch cover, I effectively embed threaded inserts into the flange to bolt the cover to. When that is cured, I then carefully epoxy the assembly into the body tube, making sure my gap is evenly lined up all the way around the hatch cover.

Photo 3: Electronics Board

Photo 3 shows the electronics board, made of 3/16" plywood. It has an altimeter, Item "3", and a timer, Item "6", mounted on aluminum stand-offs available at electronics supply houses. There is a plywood vertical riser that hold two speaker quick connects, Item "2", available from Radio Shack, for quick attachment of the ejection charge leads.

The ejection charge wiring harness, Item "5", feeds current from the altimeter to the quick connects, with safety leads for the firing circuit shunt connecting through Item "1". Item "7" points to one of the two attachment screws for mounting this board on the mounting plate which is epoxied to the motor mount tube. Item "4" points to the GE/Sanyo 9v NiCad battery, which is a must for high-current cluster ignition of composite motors.

Photo 4: Electronics Board Side View

This photo shows the side view of the electronics board, again pointing out the altimeter firing circuit shunt connector, Item "1", the altimeter wiring harness, Item "2", and the aluminum stand-offs used for mounting the electronics to the board.

Careful selection and assembly of components makes for a satisfactory result. Hopefully you will have equally as good results.