Please Explain "Cable Cutter".

I always hear the term Cable Cutter bandied about as if everyone just knows what it is.
I do understand that it is part of a Dual-Deployment set up, but other than seeing the pictures of them on the aerocon site and others, I don't really understand exactly how they do what they do.
Does anyone have a moment to show me how/where they are installed in the recovery gear and tell me about how they do whatever it is they do?
I did a search, but could not find much in the way of answers.

Thanks.

[video=youtube;qjIDk5Z6WIA]https://www.youtube.com/watch?v=qjIDk5Z6WIA[/video]

Thanks!
That's pretty slick!

I'm a ways off from needing such a device but at least now I won't be in the dark when I hear about them.

They take some getting use to, but are an excellent device once you get the setup down.

Last weekend at the Radical Rocketeers launch Jim Z. used one...
He got the entire flight perfect on the first shot..
It was a Formula 54 if I'm not mistaken..
They're really cool Top,,,
The altimeter separated the rocket at apogee,,
it came down in 2 pieces with a snugly tied bundle flapping around..
At 700 ft or so the bundle opened up and the main unfurled and filled with air...
Perfect flight...
I bought a pair of them on the last Black sales,,
but haven't had the chance to try them just yet...

Teddy

I ordered the "redundant pack", an additional Q2G2 cap, and a bunch of other stuff after reading this thread.
Thanks to TopRamen for asking a question that I should have asked, and to Crumb fire for the reply.

I have not needed dual deployment yet, but have done a lot of looking into the cable cutter and believe it will be my first choice when I do (we'll see, there's still plenty of time to think about it before I get that far).

One of my questions about it is how many have had failures because the e-match was strained during the "drouge" sequence of the flight? I could see all the "flapping about" and twisting of the bundle taking a toll on the thin wire of the match or the adequate seating of the match head on the black powder charge or on the terminal connections to the avionics.

455 Buick said:

I have not needed dual deployment yet, but have done a lot of looking into the cable cutter and believe it will be my first choice when I do (we'll see, there's still plenty of time to think about it before I get that far).

One of my questions about it is how many have had failures because the e-match was strained during the "drouge" sequence of the flight? I could see all the "flapping about" and twisting of the bundle taking a toll on the thin wire of the match or the adequate seating of the match head on the black powder charge or on the terminal connections to the avionics.

Click to expand...

You are correct in that flopping and twisting and pulling could damage the match or connection to it..
All should be secure,, tied up,, restrained,, the wire should be longer then the distance to the terminals and restrained just before it gets there..
Same on the cutter side...
If all is secured well and where it needs to be,, this should be a non issue...

Teddy

I did my Level 2 with a cable cutter after several test flights on smaller rockets and a failure on my first level 2 attempt (more on that later). What I've found is that it's best to have the main chute and cable cutter on a separate short (2-3 feet) shock cord attached directly to the Nose cone bulk plate - after separation that can flap in the breeze like a mini drogue and not get tangled up. I've never had a failure of the CC itself but have had issues with tangling etc.

Teddy makes cords with a third loop 5 or so feet from one end and I use that but double it up the smaller section to get the required length (his shock cords are excellent BTW). I use crazy jim's long wire starters secured at the nose cone bulk plate (so there is no tension on the connection at the altimeter and ensure the starter wire is loose compared to the shock cord length. Then I wrap tape around the cord and starter wire several times along the length of the shock cord to hold everything together and not tangle.

The downside to using a CC is that if you have a non-optimal flight (motor cato, ballistic trajectory, whatever) on a larger rocket (and chute) and your first separation charge happens while the rocket is travelling some speed then there is a good chance the cable tie will break and your main will deploy too - possibly at a speed which destroys your main chute. I had that happen at Balls23 with a Cato 1 second into a K flight on a 3" rocket causing separation and premature deployment at approx 400mph and 1000ft. Followed by a swift descent on a shredded chute. The rocket popped a fin on landing, was repaired and flew great a couple of months later for my Level 2 with a new chute.

Thank you,, Thank you,,
That's a good idea for setting up a cable cutter..
And I'd make a harness with the 3rd loop anywhere you'd like it,, close to the end for this set up..
I think the cable cutter is a fantastic idea,, but can be tricky setting up..
That's why I was so impressed that Jim Z at my home field got a perfect flight
on the maiden flight for the rocket AND it was flying dual deploy on a cable cutter with the altimeter in the nose cone...
Very cool...

Teddy

from what I've seen e-matches come with various lengths of wire leads, the two types I know of can be had with 3' or 6' leads.
Rex

The "burrito wrap" method that everyone uses can be improved upon. It relies on the cable tie being tight enough to keep the burrito from coming undone when exposed to the airstream. Full sized parachute systems use positive retention systems to prevent early deployment. Here's my take on it:

Nomex modification for use with a cable cutter

Zebedee said:

The downside to using a CC is that if you have a non-optimal flight (motor cato, ballistic trajectory, whatever) on a larger rocket (and chute) and your first separation charge happens while the rocket is travelling some speed then there is a good chance the cable tie will break and your main will deploy too - possibly at a speed which destroys your main chute. I had that happen at Balls23 with a Cato 1 second into a K flight on a 3" rocket causing separation and premature deployment at approx 400mph and 1000ft. Followed by a swift descent on a shredded chute. The rocket popped a fin on landing, was repaired and flew great a couple of months later for my Level 2 with a new chute.

Click to expand...

Thanks for asking the question TR. I had my own visions of how it worked, and this wasn't it.

I was thinking that there would be a drouge deployed at apogee, and the main would be on the same shock cord, but held back (inside the recovery bay) by the cable until the cutter severed it, allowing the main to pull out and deploy.

Okay, so, I'm digging this cable cutter idea, but, I have a thought. (One of those "stupid questions" :wink:

In light of the whole "green" thing, and not wanting to make more of a mess than necessary: does anyone know of any makers of biodegradable cable ties?

I mean, yeah, in the grand scheme of things, it's not that big of a deal, but every little bit helps, right?

I saw that - you've definitely protected against the bundle not being tight enough but I don't think it resolves the failure mode I saw since it still relies on the strength of the cable tie surviving the rough deployment.

ChrisAttebery said:

The "burrito wrap" method that everyone uses can be improved upon. It relies on the cable tie being tight enough to keep the burrito from coming undone when exposed to the airstream. Full sized parachute systems use positive retention systems to prevent early deployment. Here's my take on it:

Nomex modification for use with a cable cutter

Click to expand...

YodaMcFly said:

Okay, so, I'm digging this cable cutter idea, but, I have a thought. (One of those "stupid questions" :wink:

In light of the whole "green" thing, and not wanting to make more of a mess than necessary: does anyone know of any makers of biodegradable cable ties?

I mean, yeah, in the grand scheme of things, it's not that big of a deal, but every little bit helps, right?

Click to expand...

Some hemp twine might be a substitute. Would require lots of ground testing. Always a risk that it catches on fire from the ejection charge, but probably not a high risk.

Caveat: just speculating, never tried this.

You might be right. I thought that the failure mode I had seen was because the zip tie slipped off the burrito though. There was no way to tell since the altimeter fired the CC at 500' and the zip tie was gone.

Zebedee said:

I saw that - you've definitely protected against the bundle not being tight enough but I don't think it resolves the failure mode I saw since it still relies on the strength of the cable tie surviving the rough deployment.

Click to expand...

Rex R said:

from what I've seen e-matches come with various lengths of wire leads, the two types I know of can be had with 3' or 6' leads.
Rex

Click to expand...

So how long of an e-match do you need for cable cutter?

The hemp would work if its been borated to be fire resistant. I use borated duck cloth as chute protectors. Borating the twine and cloth is pretty much the process used to make dog barf and estes wadding, I use Borax and Boric acid (roach killer powder) dissolved in hot water ( look up the NFPA formula)

timbucktoo said:

So how long of an e-match do you need for cable cutter?

Click to expand...

Depends. If you go with the OOTB config, they give you about a 1' piece of Kevlar thread to secure the cutter to the NC. Thus, a 12" - 18" igniter is plenty.

But since everyone modified everything, other configurations may work for you.

I use 1' e-matches.

every time someone says cable cutter i think of this

^

That'd work too. :wink:

You betrayed Sheba, No chute for you!

With something like this, can it be as simple as having the cable cutter on the chute and an altimeter stowed in with it, or fastened to the nose cone somehow? I guess what I am getting at is if this could be readily retrofitted with to an existing single deploy rocket that doesn't have an electronics bay or holes drilled in the air frame for the altimeter without any other modifications. It seems to me that if the altimeter's sole job was to operate the cable cutter, it would already either be out of the body tube or at least well exposed to ambient pressure when it needs to be, since the nose cone and harness will already be deployed. Am I thinking about this wrong or perhaps over/underthinking it? I could see employing something like this on a few of my rockets that aren't otherwise designed for dual deployment, however due to potential apogee altitude, would find dual functionality useful...

No. The altimeter must be encased so that the gasses and particles from the deployment charge do not damage it. Also, I don't believe that altimeters can accurately assess atmospheric pressure in high airflow situations. (Most altimeter manuals will advise against making the sensor holes too big.)

The ideal way to do this, and the way it is designed, is to put an altimeter bay in the nose cone.

There are options for that. Missileworks sells a nose cone with built-in AV bay. Landru sells altimeter sleds that might mount in a nose cone. John Coker's site has a video on how to build a plywood Av sled for a nose cone.

The advantages of a cable-cutter are:

• No coupler required.
• No payload tube required.
• No drogue chute required.
• Motor ejection and tiny amount of BP for the cutter saves your BP.

However, modifications to the rocket must be made to accommodate the altimeter.

OK, well, modifying the nose cone may not be too bad, given the advantages of the set up. So, it would be a matter of finding or fabricating a sled for the nose cone being used?

The only concern I have with that is adding nose weight to a model that's already adequately stable. I try to keep the margin on my rockets comfortably over 1:1, but no higher than that in order to minimize weathercocking. Adding an altimeter sled to the nose would obviously work against that, possibly pushing well into overstable. Maybe I'm overthinking that too; I suppose flying upwind minimizes the distance down range to floats...

Good point. I guess I would say that the need for a cable-cutter probably stems from wanting to go higher on bigger motors. For me, in my leviathan, putting an H54 3G in the aft was compensated for by putting a light AV sled in the nose.

I used a modified John Coker method, with a cardboard coupler, and luan. I didn't see the need for aircraft-grade plywood. A luan sled, bulkhead, and CR, three brass screws, and a cardboard coupler. Remember, if you cut off the plastic shoulder, that eliminates weight, too.

Do your math and see what you can come up with.

That's the thing - right now, I generally keep my flights low to keep the drift minimal. I don't really have any interest in a full dual deployment set up because it adds a level of complication and cost that (to me) detracts from the simplicity and enjoyment of the hobby. But this might offer a useful middle ground, or (potentially) a stepping stone to more elaborate hardware. But right now, I just want to take models / designs I already have and be able to fly higher and get them back down again reliably.

I just watched his video on the topic, and agree that for some of my applications, what he did would be overbuilt. But it could be scaled down to something lighter as appropriate. It certainly looks like something within the realm of what I can fabricate myself. I do like the notion of designing a single compact bay and being able to use in multiple similar sized cones.

One more tangential question - if I did this, and used the altimeter really just as a means of signaling the cable cutter, can the vent holes for the altimeter be through the AV bay mounting bulkhead at the back of the nose cone, rather than through the side of the cone? I can't think of a reason that it would be a problem, but I don't yet know what I don't know...

TopRamen said:

I always hear the term Cable Cutter bandied about as if everyone just knows what it is.
I do understand that it is part of a Dual-Deployment set up, but other than seeing the pictures of them on the aerocon site and others, I don't really understand exactly how they do what they do.
Does anyone have a moment to show me how/where they are installed in the recovery gear and tell me about how they do whatever it is they do?
I did a search, but could not find much in the way of answers.

Click to expand...

Top, technically what we're talking about here is a 'reefing line cutter'. Go Google 'reefing cutter' or 'reefing line cutter' (you'll get two (slightly) different results with those search terms) - ignore any hits referring to sailing. Note, also, some good sources at any 'DTIC.mil' domains ('Defense Technical Information Center' -- a good source).

-- john.