Two-stage with PET2+ Timer, Help

[joey]

Hey guys,

I am working on a two-stage rocket with I205 for booster stage and H135 for the sustainer.

The only part I am not certain is about the stage separation. I do not have Magnelite pyrogen to make low-current requirement ignitors. So I am using just the stock ignitor that comes with the H135 motor. I have wired two 9V batteries in parallel as PET2+'s power supply to make sure it will provide enough current. But I am not sure if the stock ignitor, which we usually fire using car batteries will work with the wiring I have right now.

I am also not sure if PET2+ can provide enough current through the port directly. There are two kinds of circuits in the manual and apparently I am using the low current one.

Has anyone used PET2+ before? Please help me out, much appreciated.

 

[Titan II]

The stock igniter for a CTI H135 is fine with a single 9v battery. I I frequently fly 2 stage with CTI motors and only use the stock igniters.

 

[joey]

Thanks Titan! But I am actually using Aerotech H135W motor. Not sure if that will be a significantly different from CTI's.
A side question: do you think it is better to ignite the motor first or pop the stage with black powder first? How did you time these two events?

 

[Titan II]

I do them at the same time using the aux channel of a RRC3.

 

[cerving]

The Aerotech igniters are basically pyrogen-dipped ematches, you should be fine with a new 9V battery. Most CTI motors have a BP pellet pressed into the top grain so they don't need a dipped ematch.

 

[joey]

That is good news, thank you Cerving!

 

[Wayco]

I'm using a PET2 in a 3" two stage rocket, along with a Stratologger for separating the interstage coupler from booster at apogee and firing a cable cutter to release the boosters main chute at 700 ft.
The PET2 is just firing a separation charge in the top of the interstage coupler to separate the booster from the sustainer.
My understanding is that no RSO will allow a simple timer to fire the sustainer motor. I'm using an RRC-3 aux. channel in the sustainer to airstart it's motor only if the rocket attains a specific altitude in a certain amount of time. This is determined by simulating the flight and programming the RRC-3 with the parameters in that sim.
There is a whole 'nother thread about this here:
https://www.rocketryforum.com/showt...cting-a-first-two-stage-high-power-rocket-kit

Airstarting a composite motor in a sustainer (2nd stage) after the booster is done with it should only be done if the rocket is still going UP. A PET2 timer cannot determine if this is happening, it just starts the motor at a specific time.

 

[joey]

Hi Wayco,

Thank you for the advice. I do have a RRC-3 but I was gonna use it for dual deployment but not for air start. I did sim in open rocket and calculated the exact time when sustainer motor needs to be ignited. I did not know altimeters can be used to trigger motor ignitors as I thought they are only built to ignite bp charges.

Joey

 

[Wayco]

The RRC-3 has an "aux." channel designed to do an airstart. It's a bit tricky to program, but has a "comparator" function that help the altimeter determine if your flight is going according to the simulated flight plan. There are several other altimeters that can do this, including Chris Erving's Quantum and Marsa Systems Marsa54. I believe the Raven has four channels, which might allow you to do dual deploy, airstart and a separation charge with one unit. The only one I'm familiar with is the RRC-3, so I can't really give you any comparison between the units.
Might be a good thread to start if you want. Plenty of fliers on this forum with a wealth of info. on the subject.

 

[joey]

Hi Wayco,

Thank you so much for the detailed suggestion. But I only bought the RRC-3 itself without LCD module or USB interface module. Is there anyway I could just access AUX function on RRC-3 without buying all those add-ons?

 

[Wayco]

Hi Wayco,

Thank you so much for the detailed suggestion. But I only bought the RRC-3 itself without LCD module or USB interface module. Is there anyway I could just access AUX function on RRC-3 without buying all those add-ons?

I don't believe you can program the aux. channel unless you have one of the interface devices. This would be a good question for Jim Amos, owner of Missleworks.
He's a member on this forum, screen name "MWC".
He can also hook you up with accessories for the RRC-3.
Did someone tell you flying a composite two stage rocket was gonna be cheap? :rofl:

Twice the fun, 10x the difficulty....

 

[cerving]

The best thing about two-stagers is how you feel right after the sustainer lights. It was almost as good as the first time that I recovered a rocket in the middle of sagebrush a mile away from the pad with the prototype Eggfinder.

 

[joey]

Sorry for the late reply, but I will start a new thread for PET2+ and RRC-3 comparison. After all PET2+ is designed for mid-air start, there might be something I am missing here.

And you are right , two stage rocket is not gonna be cheap .