I'm building a 3 stage rocket which inherently by design needs the timers in the sustainer with igniters running outside the minimum diameter airframe. I need the igniters to "break" at the mid body break for motor ejection. Anyone do this before or something similar? What should be done to prevent the igniters still attached to the sustainer from upsetting the flight? Any good companies for plug type switches like headphone jacks which are stable under Gs and can handle 9A from a timer?
Trustworthy Power Jacks
Jun 02, 2006
5 Replies
You didn't say how big your rocket is, or more to the point how much thrust/ejection charge will be available to separate the stages and how much vibration the connections will have to handle.
I've successfully used small .100" headers with sockets (like what's used to connect a PC's speaker to the motherboard), in large model rockets. The header plus small-gauge wire (24 ga) is light enough that it won't pull free under acceleration.
I've also used short lengths of thin brass tubes. A 1/16" K&S tube slides just right inside a 3/32" tube. I tin the end of each wire with solder, insert into the end of a tube, then heat the tube to remelt the solder for a good connection. Crimping the tube also works.
First of all, headphone type gacks are neither high current nor hi G stable. They have no place in HPR except as audio output from a video system.
Take a look at "Jones" plugs and sockets. Banana jacks and Molex connectors are also good for power.
Which reminds me of another alternative. Standard RC servo / charge jacks. Something like Deans plugs should work for this application.
DB-9 connectors work under a shroud, I've used that approach at about Mach 1.7.
Assuming your recovery will work even if the airframe doesn't separate, you could just put a break in the igniter wires below the hole where they exit the timer chamber, twist them back together (with an offset along the two wires to avoid shorting), and put a piece of PVC tape over the joint to support the wire.
What igniters are you using? What's the all-fire current on them? 9A sounds rather high. You can dump that sort of current after the igniter has actually fired (through the plasma before the wires exit the motor) but I'd guess you only actually need to source 1A. That's the figure for a Daveyfire N28F which is what we always used to use to light Aerotech motors over this side of the pond. I think the igniter you get with a Cesaroni motor takes a lot less than that.
Chris
I've used ?Deans Connectors? for break away connections in multistage and airstart rockets from H to M impulse. Available from most R/C aircraft vendors, including:
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Jay Calvert
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