Running charge wires down main tube, will it tangle with chute?

It does create an entanglement risk.

Why not run a conduit of some sort down the inside of the tube, to keep them in place, and drastically reduce the risk of entanglement?

-Kevin

I've been thinking of the same thing -- for example, a soda straw glued to the inside of the body tube down as far as you need it (obviously, placed low enough for the payload coupler).

But, in thinking about this, it leads to other problems. For example, if the wires 'stick' in the straw (or tube), will they prevent separation of the wires/leads? So, what I'm thinking about is a modification (this is blue-sky thinking, I haven't actually done this yet). I used to use some little press-in terminal points on circuit boards for test points, that were made in such a way that you could insert a wire into them and then pull them out. If I were to mount a couple of those on the bottom side of the bulkhead, and then simply insert the ematch wires into them, then when the nose cone separates, the wires would simply pull out of the bulkhead, and either fall freely by themselves or stay in the 'conduit' in the inside of the body tube. If I can't find those terminals, even using a common two-pin Molex connector would probably work just fine.

I'll see what kind of terminals I can find, and give it a try at some point. Any comments?

David Erbas-White

I was thinking of this about the time I ran out of time and money for rocketry. Never built it, but here's the essence of the idea:

My design was/is "zipperless" and the charge was to be in the front, firing rearward. However, I wanted to launch a tiny missile-like sustainer from each fin tip at intervals during coast, controlled by the timer in the payload section. To do this I was going to run wires down the side of the tube in a thin bead of epoxy, possibly laid into a groove cut in the thick tube. I found connectors designed for computer CPU fans that fit on jumper pins, and proposed to epoxy two stiff pins on the edge of the body tube, overlapping the coupler so they didn't just hang out to catch on things. When the rocket separated for deployment, the connection would be pulled apart and broken, preventing accidental launch of the "missiles" after deployment.

If you used a connector of this kind for the deployment itself, obviously the charge would already be ignited when the connection was broken. It might be a little tricky to connect the charge to the other end of the wire down inside the tube, but there's no other reason to keep the pigtail connected to the payload section out where it can tangle, after deployment. It could probably be taped to the inside of the main body tube with 2" masking tape rather than permanently glued there, so that you could pull it out to connect the charge and then just smooth it down in there.

Just a suggestion...

That's exactly what I had in mind.

I don't like the idea of yet more connections, as those really are your weak points, where you introduce yet MORE opportunity for failure. What do those connection points do under various G loads? Can inertia cause the leads to pull out prematurely?

If you minimize the free lead length available, you minimize the amount of leads available for entanglement.

-Kevin

I like the conduit idea. ...As far as lead lengths... I don't really have too much choice. The electronics are in the payload section and the leads need to be long enough to get the charge under the chute bag/cloth.

So who is going to be the first to use onboard 802.11g or Bluetooth?

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

Watch out for Ohms law! Any time you have long wire runs make sure you account for amperage drop due to resistance. And don't forget resistance at the connection points (possibly made worse by ejection gunk over time). I've become very familiar with the consequences of disregarding Ohm's law.... Other than that caveat, copper tape sounds like a good idea.

Don't leave any more excess than you absolutely have to.

-Kevin

This thread caused me to rummage through a collection of storage boxes to drag out some design notes for a rocket I never got around to building which had a similar requirement to fire an ejection charge that was under the parachute.

As someone else posted, metallic copper tape is available. I learned about it in college when I took a class in stained glass construction to take care of one of my electives.

My design used two strips of the tape, one on each side of the body tube to carry electricity from the firing circuit (which is a 555 timer) into the fin can where the BP charge is located. When activated the stage pops of without worrying about a connector hanging up or getting long wires tangled up in the shrouds.

The copper foil tape comes in widths that step up in increments of 1/8th inch IIRC. Available at any art glass shop for a few bucks a roll. One roll will last a lifetime :-)

John

Once upon a time, I had several rockets with wires inside the tube. They actually ran to a Deans connector at a PML piston and I never had any trouble with tangles. The Deans connectors are very tight but will pull apart during ejection.

I recently did a number of altimeter flight tests using an Aerotech Initiator. I ran the wires as you describe and had no trouble.

Thank you.