First Av Bay

[Marsman]

I'm working on constructing my first electronics bay, 2" in diameter containing an RRC2 altimeter and Perfectflite MiniTimer. The rocket is also 54mm in diameter and is flying on a G staged to a G. The first flights will help me to gain experience using the dual deploy altimeter on just the sustainer before adding the booster and the timer.

I have three questions:

1) Where is the best place to get a supply of black powder for ejection charges?

2) If using the twist and tuck method, do the wires stick out of the altimeter vent hole or do I cut their own hole and do I have to seal that with tape before launch?

3) What is the best method for ground testing the entire system?

Thanks in advance.

 

[MarkM]

1) Gun Shops, Bass Pro Shops. You do realize for use in rocketry you need a LEUP, but most of these places don't ask to show those credentials. You can also use some of the smokeless powders like Triple 7 which do not require the LEUP but require tighter confinement.

2) I cut a hole to pass the wires through. Vent holes in a 2" ebay are going to be small. It will be easier to pass the wire out a larger hole. Once I tuck them back in I seal the hole with electrical tape. If you use a separate hole for the wires you absolutely need to seal it because now you'll have too much hole volume and ebay may pressurize too quickly...it result in early deployment. If, however, you use one of the vent holes for the wires, then you should not cover it up once tucking the wires back in.

3) There was a thread on here not long ago on this issue. Prepare the rocket in flight ready status....chutes, cords, quick links, etc all packed and connected. Load the charges and use an estes igniter and controller to set off the black powder. You don't test the altimeter here...this is just to determine if the amount of black powder you load is enough to separate the tubes and expell your recovery gear. Test the altimeter separately in a pressure bottle to make sure it's working and will fire the ematches you intend on using.

 

[Handeman]

Mark pretty much hit everything. I found FFFFg powered for $10.95 at Gander Mountain. I run the wires out the normal vent and just tuck them in as far as they go. If a little of the wire sticks our, I don't worry about it.

As for ground testing, It depend on what you are testing. If you are only looking for the amount you need to eject, you don't need the powder right now.

 

[mattvd]

2) If using the twist and tuck method, do the wires stick out of the altimeter vent hole or do I cut their own hole and do I have to seal that with tape before launch?

New to DD . . . .

Is question #2 referring to actually connecting the wires to arm the altimeter on the pad? I have added a small switch to my altimeter/battery connection. The sled is lined up so that I can use a small screwdriver to access the switch through a vent hole in the coupler.

So . . . I am NOT a "twist and tuck method" . . . right?

Thanks.

 

[Sailorbill]

New to DD . . . .

Is question #2 referring to actually connecting the wires to arm the altimeter on the pad? I have added a small switch to my altimeter/battery connection. The sled is lined up so that I can use a small screwdriver to access the switch through a vent hole in the coupler.

So . . . I am NOT a "twist and tuck method" . . . right?

Thanks.

My only suggestion is do something to ensure the screwdriver will not contact the circuit board of the altimeter as this could cause problems if it shorts the wrong traces or damages something. Depending on how hard it is to move the switch you could use a plastic screwdriver.

 

[mattvd]

Bill -- thanks for the tips. The board is laid out with the Alt at the top, battery at the bottom, and nothing but the big-easy-to-push-switch in the middle. Little chance of touching the electronics. But still -- I will find a non-conductive "poker" for setting the switch.

 

[blackjack2564]

Also.....the twist and TAPE....instead of tucking the arm wire back into the bay, you can tape them to the outside of the alt bay.

This allows you to disarm the system if need be, without disassembling the rocket. I only "tuck" them inside on mach flights. I have never pulled them off the rocket yet, due to flight speeds.

 

[Viperfixr]

I just powered up my new MW RRC2 Mini for the first time and programmed it today. This is my third altimeter after using a PF MAWD and a FA Parrot v1 before. It wasn't nearly as difficult as I had heard or expected; I think it will be a great altimeter. Within minutes I had both profiles programmed the way I needed. The only thing I miss is being able to visually check the main AGL altitude and mach delay like with a MAWD.

I bought some simple LEDs from a local Radio Shack, put them into the drogue & main outputs, and using the "output check" diagnostic mode triggered each one--and the light showed it was working just fine. You can also use these to test input continuity too--works great.

It's not a substitute for full-up ground testing, but it is an easy way to do a basic test anywhere.

 

[Marsman]

Continuing the black powder questions, is Pyrodex FFG or Hodgdon triple 7 FFG suitable for ejection charges? The rocket is 2.1" in diameter and I intend on using Quest Q2G2 igniters for the ejection charges.

 

[Handeman]

Yes and no. Pyrodex is a version of smokeless powder that has been "reduced" so it can be measured by volume like blackpowder. What happens with pyrodex type powders is that all of it doesn't burn unless it is contained during the burn. If it isn't contained, it will blow a lot of unburned grains away and the force will be reduced.

With black powder you put some in a container with an ematch and it is good to go. With pyrodex type powders you need to wrap several layer of electrical tape or similar containment around the container to ensure a proper burn and the right amount of gas.

No, Pyrodex can't be used the same as black powder.

Yes, Pyrodex can be used as ejection charges with the proper containment of the charge to ensure proper ignition of all the grains.

Always ground test ejection charges and if you are using Pyrodex, ground test a LOT more to make sure, not only that you have the correct amount, but that your containment is sufficient and consistant.

 

[Marsman]

Thanks.

I'm planning on using a PVC cap with masking or electrical tape over the opening to contain the charge until it fires, at which point it will blow the tape away. Are you saying that I should have 2 or 3 layers of tape for Pyrodex vs. 1 or 2 for black powder?

In addition, how critical is it to have FFFF powder? Can FFG or FFF be used to nearly equal effectiveness?

 

[Handeman]

FFg and FFFg can be used instead of FFFFg. They have bigger grains and the larger the grain, the longer they burn and the more hot burning material is heading toward you recovery gear. Where FFFFg will leave a black stain on your nomex shield, the FFg can burn a hole through it. That's been my experience.

As for holding the powder in the PVC cap, the black powder only needs to be held in place during boost and de-accel. As long as it's in place when the e-match goes off, your good. If you can do that with one piece of tape that's fine.

As for the Pyrodex, you have to contain the burning mass until all the grains are ignited. If that takes 2, 3, 4, or 5 pieces of tape, I can't say. Ground Test, Ground Test, Ground Test, Ground Test, Ground Test!

I would recommend making a lot of test with the same amount of powder and vary the amount and method of containing the powder. That will tell you the method of containment that is required. Then you can vary the amount of powder for different volumes. But still GROUND TEST!