This chapter covers the construction of electronics bays inside the coupler of a payload tube. I was working on a 54mm minumum diameter rocket which needed an electronics bay for the altimeter, and wanted the electronics accessible, as well as making it simple to install the main chute recovery system and both ejection charges. So, I made this electronics bay totally removable and able to be disassembled!

The pieces

In this photo you see all of the components assembled into sub-assemblies.

Arrow 1 points to the retaining plate that is mounted in the payload tube. It is made with a blank 2.15" centering ring drilled for a 29mm motor mount. It has two 10-32 T-nuts installed in it.

I ruined two centering rings on this one piece until I figured out to install the T-nuts before I drilled the center 29mm hole. The seating of the T-nut prongs was splitting the fragile plywood ring.

I use a seating process to brad over the T-nut prongs by placing the T-nut into the hole, placing a solid metal support under it that has a corresponding hole of similar size then I firmly hammer the T-nut into place.

There is a rectangle of 1/16" G-10 that mounts the altimeter with two lengths of 3/16" carbon fiber arrow shaft, indicated by Arrow 3, epoxied at either side for the threaded mounting rods to pass through. The G-10 mounting board and carbon fiber tubes are epoxied to the plywood lower cap as well. A 1/4" eye-bolt runs through the end cap and the nut is epoxied in place.

Arrow 4 points to the 10-32 threaded rods that holds it all together.

Arrow 5 is the 2.15" coupler tube sanded for an easy fit.

Arrow 6 is the upper end cap, again made from an blank 2.15" centering ring and a 2.15" coupler bulkhead plate epoxied together with a 1/4" eye-bolt installed. This plate is removeable.

You will want to drill all of your holes for the threaded rods at the same time by running a 1/4" bolt through all plywood plates to hold it securely while you do your drilling. This insures that your holes all line up correctly. Only on the two coupler bulkhead plates (the inner parts of the end caps) will you drill the threaded rod access hole large enough for the carbon fiber shafts to pass through.

One of the larger 2.15" plywood rings will be drilled large enough for the threaded rod itself to pass through (the upper end cap) and the other will be drilled large enough to go over the barrel of the T-nuts (lower end cap).

Assembled unit

With the board assembled, you can see how the final assembly would look with the outer cover off. The forward most plywood ring is the part that is epoxied into the payload section. The electronics bay slides in over the threaded rods with the coupler tube in place, the upper end cap installed and the lock nuts secured. Done, ready to fly.

Back of mounting plate

On the backside of the altimeter mounting plate, you can see where the ejection charge for the main chute goes. Arrow 1 points to a section of 1/2" launch lug, capped with a plywood plug epoxied in place and itself epoxied into the forward end cap. The charges made in another How-To class on ejection charges using the pants hanger tubes are a perfect fit into 1/2" launch lugs. The wires feed through the hole in the end and are secured to the mounting terminal indicated in Arrow 2.

Arrow 3 points to the Deans connector that feeds power for the drogue chute ejection charge through the upper end cap and into another mounting terminal indicated by Arrow 4. Note the carefully cut out semi-circle under Arrow 3, which allows room for the eye-bolt retaining nut.

The lower end cap

In this picture, you can see the lower end cap, the access holes for the threaded rods and the 1/2" launch lug ejection charge holder indicated by Arrow 1.

The upper end cap

In this picture, similar to the previous one, you can see the removable upper end cap with the access holes for the threaded rods and the mounting terminal to connect the drogue ejection charge indicated by Arrow 1.

Final layout of the pieces

This final photo shows the sub-assemblies again, with the portion that is mounted in the payload airframe tube indicated by Item 1. Before mounting Item 1, you should cut a relief notch where the main ejection charge contacts the mounting ring to allow room for the gases to slip by.

Usage is straight forward. Install an ejection charge in the main charge mounting tube, slip the main chute recovery harness through the hole in the ejection bay mounting flange and attach to the electronics bay. Then slip the bay in place, guiding the threaded rods through the unit and secure the lock nuts. Wire the drogue ejection charge and go.