Charge Well Design

Hey TRF,
For electronic parachute deployment, I am placing charge wells on the top and bottom of my altimeter bay. I would like to know what you all use for the charge wells themselves. Do you use PVC caps, copper plumbing caps, something else? I'm a little concerned that PVC caps will burn/melt over time. If you use PVC or copper caps, what sizes work well for you (I am flying a 4-in rocket).

Thanks in advance!

I'm using 3/4" PVC caps for my 2" diameter, it can actually hold quite a bit of charge, but for a 4" diameter 1" caps will do you quite well.

I've used 1/2" standard PVC in my 4" rockets. Multiple flights with no visible deterioration (a little dirty, perhaps).
-Ken


Why would you need a 1" cap for a piddly little 1g charge? I've never used more than about 1.2g and the 1/2" caps end up mostly full of dog barf and sealed over with masking tape.

I feel that the extra size allows for more dog barf to help with the pressure build up and allow more purchase for the tape, that was my thoughts at least

Edit
Also, I like the stand off distance from the recovery point from the taller caps, but yeah, you don't need a big cap for the charge size

I dont put charge wells on the bottom of the bay anymore. I run an extension wireto a charge I place beneath the chute to push it out and not push it in. pvc caps on the top work great

If you choose to use a canister, this is 1/2 PVC that was used in a 4" rocket with many flights and no deterioration (unflown at time of the picture). Though it worked fine, I have since eliminated most all canisters.

I used 3/4" copper caps on my 3" and 4". When I ended up using the same thing for my 6" L3, I realized I could easily get by with 1/2" copper caps on the smaller rocket. The 3/4" Copper caps hold 5g of powder with plenty of room for dog barf. Probably be able to do 6g in the 3/4 caps.

I got small PVC caps from Apogee Rockets. I trust Tim to provide the right hardware, so I'm pleased with them. Haven't launched yet, but haven't heard anything to the contrary in using them.

I have been using the Dog House rocketry charge wells on my 2.6 to 6 inch rockets.

https://doghouse.blastzone.org/charge-wells.html

I use either the Doghouse PVC charge wells
or I make them out of a 1/2" copper pipe cap
and an inch or so of 1/2" copper pipe sweated to the cap...

Teddy

onebadhawk said:

I use either the Doghouse PVC charge wells
or I make them out of a 1/2" copper pipe cap
and an inch or so of 1/2" copper pipe sweated to the cap...

Teddy

Click to expand...

I've just used the 3/4" caps. The forward end of the av-bay picks up a lot of residue, even with dog barf dumped over it. Does the longer thinner caps help keep that end of the av-bay cleaner?

For a larger project I machined a charge cup with a spring loaded cap. For smaller projects I have been using a centrifuge tube capped with some wadding and high temp hot glue.

Random Flying Object said:

For a larger project I machined a charge cup with a spring loaded cap. For smaller projects I have been using a centrifuge tube capped with some wadding and high temp hot glue.

View attachment 280753

Click to expand...

Does your rocket have internet?

llickteig1 said:

Does your rocket have internet?

Click to expand...

The RJ45's are breakaway connections for a POE and interlock port. It was used as an interface for an experimental flight computer.

Randy'sRocketShop said:

Hey TRF,
For electronic parachute deployment, I am placing charge wells on the top and bottom of my altimeter bay. I would like to know what you all use for the charge wells themselves. Do you use PVC caps, copper plumbing caps, something else? I'm a little concerned that PVC caps will burn/melt over time. If you use PVC or copper caps, what sizes work well for you (I am flying a 4-in rocket).

Thanks in advance!

Click to expand...

Hi Randy,

Back in 2011 I posted some info on making charge cups out of CPVC, then sliding pre-filled centrifuge tubes into them at the field. The thing I have really come to like with this system is that all black powder measuring can be done in advance of the launch instead of fiddling with this at the field. Here are the links in the discussion and my photo description of how to make and use them:

https://www.rocketryforum.com/showthread.php?49878-dual-deployment-charge-cups&p=488676#post488676

https://www.rocketryforum.com/showthread.php?49878-dual-deployment-charge-cups&p=489288#post489288

Since that time I have had one poorly glued tube dislodge from it's cap on a hard landing (chute was tangled). I just re-glued it in. Also any rear facing tubes should have a piece of tape over the open end to prevent G forces from allowing the black powder pushing out the seal plug.

I'll +1 the Dog House wells, though I prefer these with the integrated terminals. No more holes needed into the avionics bay, and nuts that you can tighten/loosen with your fingers rather than requiring a screwdriver, etc. I always put a strip of blue-tape over the well first to help keep the BP in, then wrap that once in a strip of electrical tape. Generally the blue-tape ruptures and the electrical tape remains stuck, so I'm not leaving any scraps out in the field. My 38mm MD rocket still has a loaded well from my last launch event where it didn't get to fly, the dual wells are for a 4" rocket. The wiring harnesses are from Dog House as well.

Handeman said:

I've just used the 3/4" caps. The forward end of the av-bay picks up a lot of residue, even with dog barf dumped over it. Does the longer thinner caps help keep that end of the av-bay cleaner?

Click to expand...

Nah,, I don't think the extra length keeps the bulkhead cleaner,,
I just size the charge well according to approximately how much powder is going to be used...
In my mind you'll get a quicker more complete / efficient burn of the powder if it's stored in a symmetric sized container,,,
the powder should be about as deep as it is wide...
To that end I also pack the barf over the powder fairly tightly and put 2 well stuck down layers of masking tape over it to try to
contain the expanding hot ball of gas as long as possible so all of the powder has a chance to ignite before it's all dispersed...

Teddy

Titan II said:

If you choose to use a canister, this is 1/2 PVC that was used in a 4" rocket with many flights and no deterioration (unflown at time of the picture). Though it worked fine, I have since eliminated most all canisters.

Click to expand...

Titan,

Is that a large capacitor I see next to the flight computer? What is it's function?

So I guess I was being silly, mine are in fact 1/2" caps... Guess I didn't take into consideration they go OVER the pipe whose OD ie actually larger than the dimension already. Sorry for any confusion...

CZ Brat said:

Titan,

Is that a large capacitor I see next to the flight computer? What is it's function?

Click to expand...

PVC extension to get the rotary switch closer to the hole in the airframe.

onebadhawk said:

Nah,, I don't think the extra length keeps the bulkhead cleaner,,
I just size the charge well according to approximately how much powder is going to be used...
In my mind you'll get a quicker more complete / efficient burn of the powder if it's stored in a symmetric sized container,,,
the powder should be about as deep as it is wide...
To that end I also pack the barf over the powder fairly tightly and put 2 well stuck down layers of masking tape over it to try to
contain the expanding hot ball of gas as long as possible so all of the powder has a chance to ignite before it's all dispersed...

Teddy

Click to expand...

That's pretty much exactly how I do it too. The 3/4" caps leave a 2g charge about 1/2 to 1/4 as deep as it it wide. I've never had an issue with the powder all burning, but I think the dog barf and tight masking tape help that the most.

Thanks...

+1 on Doghouse. And Bill ships almost immediately and is great to work with. He sells a bunch of other cool stuff, too, so give his site a perusal.

MAC Performance sells aluminum wells that look very nice, though I have not tried them.

Dog House have held up for many flights for me.

I have used all the above mentioned wells and they all work fine. My preference for larger birds though is brass crimp PEX plugs, and for smaller birds cut down spent rifle or pistol casings 30-06, .300 Win. Mag, 44 mag ect ect.

This is my DarkStar extreme that uses 3/4 copper pipe caps as the charge well.

I still use my Robbys rocket charge well with flash bulbs.

I have used dog house wells in the past, and they work very well.

but lately I have switch over to plastic glove tips with tape, and I am going to be using duck tape to make a BP Burrito.
So I am going to quit using wells.

webtech said:

I have used dog house wells in the past, and they work very well.

but lately I have switch over to plastic glove tips with tape, and I am going to be using duck tape to make a BP Burrito.
So I am going to quit using wells.

Click to expand...

Because ... ?

Here's another option that I use on smaller diameter rockets but would work in larger ones too. it's a small centrifuge tube with an e-match, black powder and an ear plug.

After more analysis of my charge wells they are actually 3/4" plugs.... All they have OD of 3/4", but have a flat "cap" section so they lay flat vs the caps that were more curved. About the same size as 1/2" caps.