Building a 38mm Electronics Bay for Dual Deployment

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By Mike McFadden

I obtained a partially built 38mm rocket with a 29mm motor mount, a LOC kit of some type, but I'm not sure of the model. I wanted to build this as dual deploy but the standard way of constructing an Electronics Bay (E-bay) would be too heavy and not enough room for all-thread.

The parts:

• 8" 38mm coupler
• 7" x 1.125" G-10
• Rotary switch
• Battery holder
• PerfectFlite MAWD
• 4 38mm bulkheads
• 1 38/29mm centering ring
• 2 1" Eyehooks
• 2 Standard washers
• 2 Fender washers
• 6 small woodscrews
• Wire
• Shrink tubing

The dimensions can be altered to fit your needs. I also applied carbon fiber to the bulkheads and centering ring for strength.

Mount the battery holder to one end of the G10 using epoxy and leave about a ½" margin at the end of the G10. You may need to sand the corners of the battery holder to fit. At the other end, mount standoffs for the altimeter also leaving a margin of about ½". In between these drill a ½" hole with a spade or forstner bit for your switch. Check the diameter of your switch before drilling. In order for it to fit in the tube, the body will need to face up. Epoxy in place. Solder a black wire from the negative pole of the holder which will connect to the altimeter and a red wire to the switch and then another red wire from the switch to the altimeter.

Take two of the bulkheads and cut a slot about half way through each one with a hack saw. The G10 will slip into these slots to secure it inside the tube. Test fit your sled in the coupler and mark the plates where the G!0 sits. The slot should be about 3/8" up from the bottom center of the bulkhead.

Using the other two bulkheads, place a washer onto an eyehook and thread through the center hole, add a fender washer and tighten this down with a nut. Cut off the excess thread behind the nut with a rotary tool. Take the two slotted bulkheads and ream out the centering hole to where they will fit over the nut. Epoxy the two plates together making a ½" unit. There will be space in between due to the fender washer. Allow to set.

One of these bulkheads (aft) will epoxy into the end of the payload tube. The other (forward) will be epoxied in place to the G10. Mark a line on the E-bay where the center of the switch is. This rocket was set up as a zipperless design so the E-bay will not separate from the tubes, you can design this as a separation point if you desire. The next step is to epoxy the centering ring in the forward body tube. Apply epoxy in the tube with a dowel at the distance the E-bay will be pushed forward. Use the E-bay to push the centering ring to the correct point. Be sure your eyehook fits through the centering ring as well. Remove the E-bay so it is not epoxied in place. This centering ring will hold the E-bay assembly in place so it is critical to get the spacing correct.

Drill two small holes through each of the bulkheads for your E-match wire. You could put terminal blocks through but there is not much room to mount them, they could hang free. I just run the E-match directly, use a little clay to seal the hole.

The final step is to drill the vent holes and 3 mounting holes at each end. Your spacing my vary but I have the joint of the two body tubes just above the center of the switch.. The first vent hole will directly over the switch so you can insert a screwdriver to arm it. Drill the other two vent holes equally spaced around the tube. I used the rotary tool and small drum sander to notch the body tune at these vent holes. Then drill 3 equally spaced holes through the body tubes and into the rear bulkheads both at the aft and forward ends. Wood screws will secure these sections together for flight.

I've used this for one flight so far which was successful aside from drag separation. Next will be a 54mm by similar design, and then to see if I can get it even smaller for a 29mm.

GUEST's OPINION:
"" (X.X.)