Aerobee Hi

[heada]

About 16 years ago, I built a Cosmodrome Aerobee Hi.

https://www.rocketreviews.com/cosmodrome-rocketry-aerobee-hi-by-aaron-head.html
It's a great kit but that one ended less than ideally when the staging timer failed and the kit was destroyed. I used a PerfectFlight timer with a breakwire mounted in the base of the inter-stage coupler. This was a major design failing of mine and I have been sitting on another kit trying to decide how to set it up better. Both from a staging and safety standpoint.

My requirements are

- electronics should be in the sustainer
- minimum of 2 events, staging and backup apogee
- electronics should support safety lockouts (alt@time, vel@time, etc.)
- 2nd event is required to deploy recovery at apogee if staging didn't happen since there will be no motor deploy

I've narrowed down my electronics options to 3 that I already own. Eggtimer Quantum, Eggtimer Proton or Featherweight Raven2. I limited it to these 3 because they all have a minimum of 2 events and they have the ability to add safety lockouts on the staging event. I'm thinking of removing the Proton from the list due to it's size. It is much larger than the other 2 and I don't need the 6 event ability that it has. If I mount it between the fins, space is very limited.

My question is where to mount the electronics to support both functions. The kit has the sustainer as a single body tube so my initial idea was to add a hatch between the fins and between the centering rings. The staging connection would be done through the aft centering ring with either a pair of stainless steel #6 bolts or wires drilled and epoxied in the CR. The issue is how to make a connection for the apogee event? It will need to go through forward CR and then all the way up to the top of the body tube to allow connecting ejection charge. I thought a 1/4" tube could secure the wires and then do a variation of twist&tuck at the forward end of the BT but I don't really care for twist&tuck so I'd probably put in a terminal block somehow. I have a worry that this could interfere with the recovery harness somehow as well My second idea was to add a standard av-bay to the sustainer BT but I don't really care for that for 2 reasons. 1) making the connection down to the sustainer motor for staging is the same issue as if I mounted the electronics between the fins, just in reverse and 2) the kit includes balsa "conduits" that run from the fins to nearly the top of the sustainer BT. I would have to cut those conduits at the av-bay joints. I rejected electronics in the nose because it's actually a solid balsa turned cone and I don't want to hollow it out to mount anything inside it.

Which electronics, Quantum, Proton or Raven2?
Where to mount it? Av-bay or fin hatch?

 

[cosmodrome]

It's possible to hollow out the balsa conduits and run the wires in them.

 

[heada]

I've been thinking about hollowing out the conduits and I like that idea. I would need to have the wires re-enter the BT below the lowest point of the nosecone shoulder so that it wouldn't interfer with the nosecone. I would also need some wire exposed past where it re-enters the BT to allow me to connect an ejection charge. This means I'll have ~6 to 12 inches of wire from where it re-enters the BT going down into the BT. Would that wire be a tangle risk for the shock-cord and parachute or am I just over thinking it?

 

[cosmodrome]

I've always wanted to play around with the idea of running the wire up the conduits, go through a small hole at the mid point of the shoulder and then terminate in a thin metal plate epoxied to the inside of the body tube. Would need one wire in one conduit and another wire in another conduit. There would be matching plates on the outside of the coupler that connected to wires that would then go to the ejection devise. Three problems that I see with this that would need to be overcome. 1) The tubes would need to be modified so that the extra thickness due to the plates does not make the fit too tight. 2) Would need to prevent rotation of the coupler in relationship to thee BT. This could be done by adding a small notch to the coupler/BT. 3) Electrical contact must be maintained. larger plates would help but would also make any rotation more of an issue.

Note: I have only played around with this idea in a static environment. I have never tried to flight prove this.