The BOTC84 Electronics Bay is a standard bay constructed of Blue Tube coupler that fits inside of the main body tube. The rest of the structure is aircraft grade plywood of various thicknesses. The Tripoli Level 3 certification rules stipulate redundant deployment electronics. I will be using a Altus Metrum TeleMega 3.0 for the primary and a PerfectFlite StratologgerCF as the backup.
BOTC84 Electronics Bay
20 July 2018
The ends of the electronics bay consist of two bulkheads. One bulkhead has a diameter that matches the outside diameter of the coupler used for the bay. The other has a diameter that matches the inside diameter of the bay. Each assembly was epoxied together with slow-hardening epoxy with colloidal silicon added.
21 July 2018
- I drew three 4-inch chords from the on the joined bulkheads. Drawing a perpendicular line from the middle of the chord toward the center of the bulkhead will reveal the center of the bulkhead. I punched a pilot hole at the center of each bulkhead.
- Drilled a 3/8-inch hole through the center of each bulkhead. Drilled a 3/16-inch hole one inch above the center hole. This hole will contain the wires for the ejection charges. Drilled two 1/4-inch holes 1/2 inch below center line for the two threaded rods of the electronics bay.
- I measured the threaded rod and cut it to size with a hacksaw. Finally, I filed the cut ends down and ensured that nuts easily fit on the cuts.
- Calculated the size of the electronics bay sled and cut it from a piece of aircraft-grade 1/4 inch plywood.
22 July 2018
- Inserted a 3/8-inch forged eye bolt with a small washer on the body tube side of each bulkhead. Secured this bolt with a large diameter washer and nut. Finally, I used Loctite on the nut and set the nut with 30-minute epoxy.
24 July 2018
- Glued four washers on the outside of the bulkheads. This saves me time searching for spare hardware on launch day.
- Attached the threaded rods to the forward bulkhead with two washers, a locking washer and a nut. This end of the electronics bay will be semi-permanent. I am not going to glue the nuts, but I do not intend on taking this end of the bulkhead off for launch preparations.
- The sled of the bay will be attached to the threaded rods with 2-inch nylon spacers. I sanded the spacers flat on one side. That side will be epoxied to the sled.
- Put two spacers on each rod and placed the rods on the bottom side of the sled. After aligning the rods and spacers, I epoxied the spacers to the sled with 5-minute epoxy. Fillets of 12-hour epoxy with colloidal silica added were added to the sides of each spacer.
- Prepared the copper cups that will be used to hold the ejection charges. Drilled a 7/64-inch hole in the middle of each cap and filed the edges of the hole flat.
25 July 2018
- Attached two ejection cups to each bulkhead. I used 4-40 bolts and nuts to secure each. I also coated each screw with 5-minute epoxy to seal the hole and make the connection more secure.
- Attached a terminal block to each bulkhead. These terminal blocks will connect the flight computers to the ejection charges.
27 July 2018
- Today, I laid out the electronic components on the sled. The TeleMega needs to be oriented with the antenna pointing at the nose. The batteries for each computer will be mounted below each board. The lithium battery will be secured with tie wraps.
- Holes for the two computers were drilled for the mounting hardware. An 1/8-inch drill bit was used to accommodate the 4-40 mounting hardware.
Each computer was mounted to the board with a nylon standoff and locking washer.
29 July 2018
- The Altus Metrum instructions recommend that all wires in the electronics bay be twisted to reduce the chance of radio frequency interference (RFI). So, I took the leads that will pass through the bulkheads and connect to the terminal blocks and twisted them. Held the twist in them with shrink tubing.
- Passed two sets of leads through the hole in each of the bulkheads and stripped and secure the wires in the terminal blocks. I made sure that each set was paired with each other in the terminal blocks.
30 July 2018
- Using small tie wraps, I secured the battery wires between the 9-volt holder to the StratoLoggerCF. I also used tie wraps to secure the antenna attached to the TeleMega computer.
31 July 2018
- I am building a holder for the lithium battery used by the TeleMega. It is made out of 3/8-inch square dowel. I am securing it to the sled with #4-40 screws. To hold the parts in place, I used TiteBond III wood glue.
- The top of the battery holder is made of 1/8-inch beech wood. It was glued in place and then secured with screws. All the nuts used to secure the sled were locked up with 5-minute epoxy.
- To secure the battery in the holder, I drilled a 7/32-inch hole in front of the box on the sled. Second, I inserted a threaded insert into the hole. Once the battery is installed, I use a 7/64-inch bolt to secure the battery.
- I wicked CA glue onto each end of the electronics bay outer ring to strengthen it.
2 Aug 2018
- Determined the center of the electronics bay coupler tube and marked the boundaries of the outer ring. Sanded the area on the coupler where the ring will be attached. Sanded the inside of the outer ring.
- Spread slow-hardening epoxy with colloidal silica on the coupler tube where the ring is going to be attached. Slid the ring into place and cleaned up the excess epoxy with rubbing alcohol.
7 Aug 2018
- Added two nuts, a locking nut, and rubber bumper on each threaded rod. I did this as the sled was shorter than the electronics bay and these stops will hold the sled stationary.
8 Aug 2018
- Drilled the holes for the Binder Design screw switches. Epoxied the switches into the holes.
- Drilled the four 5/216-inch holes in the ring of the electronics bay to give access to the outside air pressure for the altimeters.
The rest of the BOTC84 rocket construction pages can be accessed from this link: The BOTC84 Rocket Build