Next Rocket

The Rocketry Forum

Help Support The Rocketry Forum:

Albanach

Well-Known Member
Joined
Jul 4, 2021
Messages
68
Reaction score
35
Location
Illinois
I am planning my next rocket starting with the avionics and the ejection charge system. The lesson learned from the Punisher is that I need to use the pull tag pins/microswitches. I am wondering if the placement of the ejection charges can be improved. Most motors come with an ejection system that pushes the parachute/drogue out. However, when people build an avionics bay they attach the ejection charges to the pod and it pulls the parachute away from the motor. So which is the better method?

I have two Eggtimer Apogee pods and one Eggtimer TRS GPS Tracker/Flight Computer. I also ordered a Missileworks RRC3 Sport.
 

sharkbait

Well-Known Member
Joined
Aug 6, 2013
Messages
503
Reaction score
57
I am planning my next rocket starting with the avionics and the ejection charge system. The lesson learned from the Punisher is that I need to use the pull tag pins/microswitches. I am wondering if the placement of the ejection charges can be improved. Most motors come with an ejection system that pushes the parachute/drogue out. However, when people build an avionics bay they attach the ejection charges to the pod and it pulls the parachute away from the motor. So which is the better method?

I have two Eggtimer Apogee pods and one Eggtimer TRS GPS Tracker/Flight Computer. I also ordered a Missileworks RRC3 Sport.

flying with electronics gives you a deployment that is very very close to apogee, motor ejection delays can vary and getting them dialed in to apogee is often difficult. Electronics allow for easy dual deploy, but motor eject combined with JLCR, tethers, or cable cutters can work also for DD. you can use a longer delay and keep your motor eject as a backup to your electronics also. As you grow into larger motors you find electronics become a requirement as the bigger motors are plugged
 

jd2cylman

Still not Carl... ;-)
Joined
Jun 16, 2011
Messages
5,724
Reaction score
1,650
All my dual deployment rockets have the charge wells on the lids except for the HED rockets. Those get the charges placed in the tip of the nose. Then the chute is always attached to the AV bay lid. Drogue charges are still close to the AV bay lid, but I just use the cardboard tubes on Tim’s lighters. Laundry always pulls out fine.
 
Last edited:

Handeman

Well-Known Member
Joined
Jan 18, 2009
Messages
7,983
Reaction score
521
Location
Stafford, VA
First of all, forget the idea that ejection charges push the chutes and cords out of the rocket. They do not. There may be some movement induced from the charge, but not much. What the ejection charge does is pressurize the tube and that pressure acts against the nose cone/av-bay to eject that from the tube.

If you have a chute packed in a deployment bag or wrapped in a chute protector and it is very tight in the BT, the ejection charge will move it like a piston until the pressure on the opposite side of it equals the pressure from the ejection charge then the pressure acts on the nose cone/av-bay.

In either case, it is the pressure on the nose cone/av-bay that opens the rocket, not the movement of the recovery system inside.

When you are using shear pins, a higher pressure is required to shear the pins, which in turn causes the nose cone/av-bay to eject at a higher energy. This tends to pull the recovery gear out better, but can cause excessive shock on the recovery system when the pieces hit the end of the shock cords.

With the pull pins and micro switches, I would recommend a screw switch in series with them that is accessed through the coupler that will be exiting the BT when the apogee charge goes off. That way you can turn off the altimeters without having to have the pull pins and flags in the way as you prep everything. Just before you head to the RSO, put the pull pins in, turn on the screw switches and close up the rocket.
 

Albanach

Well-Known Member
Joined
Jul 4, 2021
Messages
68
Reaction score
35
Location
Illinois
I have been working out of town so my rocket time has been limited. However, it does give me a fair amount of CAD time. This is my prototype avionics sled.Prototype.JPG
 

Sooner Boomer

Well-Known Member
Joined
Mar 21, 2011
Messages
4,496
Reaction score
2,466
I'm just starting in electronic deployment. I too have an Apogee altimeter. What I plan on doing is to make charge "capsules" that hold an e-match and the BP, and have about a 3 foot lead. I don't plan on using the charge well on the Apogee (it won't even be screwed on), but I *will* use the screws/washers/nuts included to hook the leads up. To prep, first the motor goes in and gets secured. Next, from the other end, the charge capsule, then the chute/protector. The leads get hooked up to the altimeter (in the nosecone), then the nosecone goes on. Ready for an igniter (at the pad), and flight! The other rocket that will use the Apogee has a small AV bay (a 4" piece of tubing and a coupler); the altimeter will go into the aft bulkhead. (the nosecone for this rocket has been modified for use with a FeatherWeight tracker). Everything gets pushed just like motor eject. In fact, I'll probably use motor eject as a backup.
 
Top