matthewdlaudato
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- Joined
- Nov 17, 2013
- Messages
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I've hinted at this elsewhere:
https://www.rocketryforum.com/showthread.php?61344-Mega-Alpha-Rebuild-thread and
https://www.rocketryforum.com/showthread.php?65896-Speculation-why-my-cutter-deploys-at-higher-than-expected-altitude
Happy to say that I have a working, reproducible, flight tested approach that works well.
The inspiration came from the endless threads about BP and the headaches around procuring it. Saw one comment about a discontinued commercial product that used monfilament (fishing line) and the wheels started turning.
Design constraints:
- Motor ejection at apogee required. If you sim your rocket correctly and know how to drill a delay, it should be possible to get an ejection event near apogee.
- No BP required for main deploy
- Must be easy to construct
- Must be reliable
Here's a closeup of the result, and a second shot showing the (typical) cutter attachments to the nose section.
The cutter consists of:
1-1/4" of 32g nichrome wire (easily obtained from Amazon and other sources)
3' of discarded igniter wire or equivalent
A 'long' bread package tie
2 shrink wrap wire covers
I thread the bare igniter wire through two holes I punch in the bread tie, slip the shrink wrap over them for later use, and then solder the nichrome wire in place. I also use some electrical tape to secure the wire assembly to the bread tie, and to secure the assembly to the outside of the nomex blanket.
The cables I use are thin beaded ties from McMaster-Carr (https://www.mcmaster.com/?orderview=new#7567k43/=sfn73d). They are more than strong enough to hold most chute bundles together, can be linked to wrap bigger bundles, and most importantly, the beaded design yields positive contact between the nichrome wire and the thin part of the cable (between the beads).
In 3 bench tests and 5 flights, the hot wire successfully severed the cable tie when powered off the 'Main' port of a Stratologger SL100 every time. Once I got the rocket design straightened out (bundle was getting stuck in a 'too long' upper payload section), smooth flying and recovery. I have another rocket on the bench (a DD mod Partizon) that will use the same approach, and can't see why it wouldn't work in nearly any DD flight that can use motor ejection at apogee.
So, if you are looking for an easy DIY project and don't want to mess with BP and its problems, might be worth giving this approach a try.
https://www.rocketryforum.com/showthread.php?61344-Mega-Alpha-Rebuild-thread and
https://www.rocketryforum.com/showthread.php?65896-Speculation-why-my-cutter-deploys-at-higher-than-expected-altitude
Happy to say that I have a working, reproducible, flight tested approach that works well.
The inspiration came from the endless threads about BP and the headaches around procuring it. Saw one comment about a discontinued commercial product that used monfilament (fishing line) and the wheels started turning.
Design constraints:
- Motor ejection at apogee required. If you sim your rocket correctly and know how to drill a delay, it should be possible to get an ejection event near apogee.
- No BP required for main deploy
- Must be easy to construct
- Must be reliable
Here's a closeup of the result, and a second shot showing the (typical) cutter attachments to the nose section.
The cutter consists of:
1-1/4" of 32g nichrome wire (easily obtained from Amazon and other sources)
3' of discarded igniter wire or equivalent
A 'long' bread package tie
2 shrink wrap wire covers
I thread the bare igniter wire through two holes I punch in the bread tie, slip the shrink wrap over them for later use, and then solder the nichrome wire in place. I also use some electrical tape to secure the wire assembly to the bread tie, and to secure the assembly to the outside of the nomex blanket.
The cables I use are thin beaded ties from McMaster-Carr (https://www.mcmaster.com/?orderview=new#7567k43/=sfn73d). They are more than strong enough to hold most chute bundles together, can be linked to wrap bigger bundles, and most importantly, the beaded design yields positive contact between the nichrome wire and the thin part of the cable (between the beads).
In 3 bench tests and 5 flights, the hot wire successfully severed the cable tie when powered off the 'Main' port of a Stratologger SL100 every time. Once I got the rocket design straightened out (bundle was getting stuck in a 'too long' upper payload section), smooth flying and recovery. I have another rocket on the bench (a DD mod Partizon) that will use the same approach, and can't see why it wouldn't work in nearly any DD flight that can use motor ejection at apogee.
So, if you are looking for an easy DIY project and don't want to mess with BP and its problems, might be worth giving this approach a try.