Apache - 2.1" (several tries)

Apache - 2.6"

Viking 7 - 2.6"

Dart - 1"

DD Modroc - BT-55

Apache 2.1"

This was my first electronics bay, and it has a lot of problems. The rocket is an Apache (as in the upper stage of a Nike-Apache) that I constructed from cardboard mailing tubes. The inside diameter is 2" and the electronics lives inside of a coupler.

I came across a nice idea for shunts on Bob Fortune's Gizmos & Doohickeys page. Bob's design uses a pair of nuts soldered to brass to shunt an ejection charge. I modified his design to put one nut on each side of the altimeter mounting board and left out the brass strips.

The major mistake I made on this altimeter bay was mounting the shunts horizontally, across the top of the altimeter mounting board. That was compounded by poor hole drilling that ended up removing about 1/3 of the airframe.

The second problem is that shunts don't provide much safety for their complexity. The resistance of the shunt isn't much lower than that of a Daveyfire E-Match. So if the electronics accidentally fires the ejection charge, the e-match will still fire!

I flew this configuration about 3 times, then scrapped it.

I completely rebuilt the electronics bay using a full-length tube coupler and a new mounting board with two switches on it for power and connecting the ejection charges to the altimeter (see below for details on the wiring harness). I now have a connection for each switch on each side of the tube, and the switch is pretty close to being centered on the tube.
However, even before flying it, I made some changes. I changed it into an open-frame configuration. Both airframe tubes are screwed to the long connector on the left and I glued two short tube coupler pieces down each side of the airframe to help stop ejection gasses from seeping around the bulkheads.

I've preped this configuration for flight twice, but only flew it once. The first time I tried, I had the drogue and main charges reversed and the drogue ejection charge (on the long coupler on the left) did not have the internal wires screwed on to it.

This is still not without problems. I really need four screws per tube to have a solid mounting. I also have a problem with the screws that engage the switches. I mounted the nuts to the side of the coupler, not to the board that the switches are mounted on. As a result, a hard landing can jar the altimeter mounting board enough to cause the altimeter to lose power. An inconvenience on landing, but a potentially dangerous problem if this should happen any time during the flight.

Apache 2.6"

On the right is the second altimeter bay I built, for a 2.6" Apache (I even planned to fly this one as the upper stage of a Nike-Apache) but the first one I actually used for electronic deployment. It is built from 7" of phenolic tube coupler (from Giant Leap) and a pair of bulkheads.

The tube coupler is held in the rocket by two 4/40 screws on each end. I glued the nuts to the inside of the tube with 15min epoxy, with limited success. I had one tear off while preparing for a flight, so I placed small wood strips along side the nuts. I haven't had a nut come off since then, but my newest altimeter bay uses JB Weld instead of epoxy.

The bay is held together two #6 threaded rods, which are glued to the inside of the coupler tube. This, unfortunately, puts the rods very close to the edge of the bulkhead and I had to file down one side of the nuts to keep them from scraping up the airframe. I'm not particularly happy with this configuration. Both bulkheads are screwed on.

Each end has a 1/2" PVC pipe coupler to hold an ejection charge cannister (I make disposable ones with PVC tubing and a dowell), a screw-down connector for the e-match and wires leading inside the tube through an epoxy plug, and a U-bolt.

I mount the electronics on a board which also holds a slide switch for power (I have access to that through one of the vent holes) and a shunt for one of the ejection charges. The shunt is a pair of #4/40 nuts which can be accessed through a hole in the side of the rocket; however, this shunt isn't even reliable. The nuts aren't tight on the screw, so it can wiggle and cause the connection to break.

Viking 7

I scratchbuilt this 2.6" diameter rocket from scale data in Rockets of the World. It was my first rocket that was built for dual-deployment from day one, and has flown with electronic deployment on every single flight (on most flights I back up the drogue ejection with motor ejection).

This altimeter bay is pictured above on the left. It's made from a pair of LOC/Precision tube couplers. Unlike my previous payload bay, I did not glue the connecting rods to the coupler. Instead they are bolted to the lower bulkhead close to the outside, but far enough in that nuts fit on well. The bulkhead is is currently taped to the coupler, but some day I'll glue it on. I used JB Quick to glue a pair of #6 nuts on each end.

The first version of this bay used 3 sets of #4 nuts as shunts, pictured here, as a power switch and shunting the ejection charges. This proved unreliable, possibly because the nuts did not grip the screws tightly, and I was forced to add a slide switch for power.

At the September, 2000 MASA meeting I saw Ted Cochran's electronics bay in which he used micro switches for the power and shunts, and a large nylon screw to turn them on. I liked the idea and picked up a double-pole, double-throw microswitch and a new tube coupler to replace the one with shunts glued inside of it.

On the right, you should see a MissileWorks RRC² mounted to a board along with a power switch, micro switch for the ejection charges, and board holding nuts above the levers on the micro switches.

The wiring harness connects the altimeter to the short / connect switch then to connector blocks which go outside the altimeter bay to another set of connectors that the e-match connects to. The switch's normally open contacts short out the wires from the e-match, and when closed connect through to the altimeter (one wire from the e-match connects to the switch "pole" through withch it is either shorted to the other e-match wire or connected to the altimeter; the other wire connects to the normally-open contact and to the altimeter).

I consciously designed this so that the switches would be held closed by screws to activate the system instead of letting the springs hold them open to activate the system. I don't trust the springs to maintain the contacts.

What I would do Differently