Chapter 1 cont.
1.6 - Recovery Architecture
The way I designed this flight was to have a drogue-less dual deploy using the piranha line cutter from tinder rocketry. 20 feet of 350lb chord would be the shock chord and that would be spliced using the finger trap method described here:
https://www.rocketryforum.com/threads/finger-trap-technique.137003/
Splicing is a much better option than knots which can significantly decrease the strength rating of your chord. When using chord that is much stronger than what you need, knots aren't going to be a huge issue but in my case, I needed to make sure that the chord retained its full strength properties.
Here is a general schematic of the setup:
The red stars are all points of attachment for the Kevlar shock chord.
This was the idea up until the day of the launch where there was some last minute changes due to fitting issues. The changes were probably the second biggest mistake made on this project and I will go into detail on that and what I am doing to correct it for the next launch.
Here is the photo of the splicing on the motor eyebolt. One thing you want to make sure of is that the finger trap splice is long enough to where it doesn't pull out. There is a general calculation based off of diameter of the chord that you can search up but I just did about 3 inches. It became so tight that I couldn't pull the rest of the chord through so I just taped the excess down. I tried pulling it out and the splice didn't let up an inch so I decided that was good enough. This was done again by splicing the nomex and parachute (always make sure that your nomex is not free floating, this can prevent a parachute from opening). Then the e-bay was attached by making a very small spliced loop that sat tightly between two nuts on the threaded rod. These were loctited in place. Finally the other end of the chord was spliced around the bolt that goes into the aluminum tip, making sure that the loop was much smaller than the head of the bolt.
Note: There are some things I need to do very differently for next flight in the AV bay area. The lower architecture will stay the same.
Being a biologist I obviously elected to use my new favorite ejection charge method of free floating microcentrifuge tube. I chopped the centrifuge tube top down substantially and then drilled a hole into the bottom just large enough to slide the wires from my e-match through. Before pulling the wires all the way through, I took some hot glue and put some on the bottom of the e-match head so that a seal was created. (Photos to come).
1.7 Electronics
Sadly, it seems that I forgot to take a picture of the final configuration but I did my best with this. The blue capacitor that belongs to the raven needed to be desoldered and then moved around the back where the green square is. This was resoldered to some thin gage stranded wire. The same was done with the green terminal block on the featherweight GPS. With these out of the way, the GPS could fit nicely in the space between the raven and the raven battery. All of the threaded rods had heat shrink tubing applied to them to prevent shorts and then wrapped with electrical tape to hold stuff together.
Note: Do not block the barometer on the raven!
The passive bulkhead was not used so that the unit could be pushed into the top of the nosecone farther.
Number 1 mistake!!!: Spoiler, the thing that most likely damaged the GPS after looking at the data points was the ejection charge. After talking to @Adrian A he believes that the hot gases from the ejection charge caused the failure. Going forward, I need to find a way to completely seal the electronics from the gas.
I thought that placing the Nomex wrapped parachute right up against the electronics while I ran the free floating ejection charge to the other side (pointing towards the top of the motor) would be enough to seal from the blast but it probably wasn't. Granted something else could have damaged the GPS but sadly there is no way of knowing without the rocket. This is just my best guess.