Help with Cable Cutter setup for Level 1

So, I'm intending to use an Archetype Rocketry cable cutter for deployment on my level 1 certification flight. However, I've heard several stories about tangled parachutes using cable cutters, and seen several different methods of setting up the recovery system described, so I'd like some advice on which method would work best for this particular rocket.

Details on the build:

The rocket is 3" diameter and 54" long, with a 38mm motor mount. With a small H loaded it should weigh around 3 lbs.

There is a single airframe section, with the avionics bay mounted in the nose cone. Motor deployment is not possible due to a solid bulkhead separating the booster from the payload section (all flights will use reloadable motors with the ejection charges removed). Ejection charge wells mounted on the back of the nose cone shoulder pull the nose cone and parachute bundle out of the rocket (this has been successfully ground-tested).

The current plan is to attach the nose cone to the rest of the rocket with a long piece of shock cord, then attach the chute bundle to the nose cone. The parachute is a 36" nylon chute from Mad Cow Rocketry, which will be wrapped burrito-style in a nomex chute protector, and the cable cutter attached as prescribed in the directions. The cable cutter's restraining strap and e-match leads will be fixed to the short length of shock cord connecting the chute bundle to the nose cone with tape to reduce the risk of tangling.

The flight will be with Northern Colorado Rocketry (i.e. about 5000 feet ASL).

For the certification flight I plan to set the main deployment altitude fairly high, around 700-800 feet, to give the chute plenty of time to deploy, then evaluate whether deployment at 500 feet is safe for future flights.

I can provide pictures of the planned setup if needed.

Hey!

I would recommend attaching the burrito with the zip tie *to* the shock cord that way it stays as a unit and cannot wrap around each other. I fly at NCR (live in Fort Collins) If you are close I'd be happy to meet up with you and go over recovery, or go over it at the launch site. I'd recommend going a bit higher on the main, I typically set it for 1000'. A long walk always beats a lawn dart.

Edward

So what's the question?

my only caution is to make certain that e-match leads and any additional wire are securely fastened to the shock cord to avoid tangling. Keep this section relatively short (I've used ~12 inches). Don't use a swivel on this section of shock cord. You may find it advisable to use redundant cable-cutters. Oh, and make sure your loose nomex isn't going to interfere with the deployment of the parachute. YMMV. I've done a similar setup with good success several times, but used motor eject to kick the parawad burrito out near the top.

As the previous post indicated, zip ties are better than tape for attachment. Also, if you have excess wire, coil it (spring-style) so it doesn't flop around.

In general, your description sounds about right.

Two things I have learned

1) put a heavy duty swivel somewhere in the recovery train. That way the bidy section can tumble and not twist up the shock cord. The closest I came to a bad recovery using the cable cutter was because of this. The swivel in the example below isn't visible as it is at the cord attachment to the Y-harness.

2) use a short second cord (6-9 inches is plenty) to attach your parachute burrito to the nose cone using the same quick link. Then use really long ematches (1 m length are good) and a dowel rod to coil the excess. Secure the match to the bulkhead somehow (I wrap it tightly around the eyebolt a couple times). Then straighten a small amount of match wire in the center and tape to the short cord.

I just set up two of these for this weekend, so see picture below. Not to jinx myself, but I have around 10 sucessful flights with this configuration.



Good luck on your flight.

I would make sure you zip-tie the e-match lead first to somewhere on the bulkhead then create a coil, not a gigantic one a couple loops is fine, then with zip-tie it along the harness with a bit of slack between each zip-tie right up to the to the burrito bundle. Once at the bundle I would again add a couple of coils then right into the cable cutter. Too many coils is just loose wire waiting to get tangled in something. If the cable is zip-tied to the harness leading to the burrito then it is limited by that harness so the excess coiling is just that excess. It looks cool though, kind of has that typical movie home made bomb look.

Dual cables cutters are a good idea, just keep in mind you need to make sure your altimeter battery is going to do that much more work. I would keep the bundle as close to the nosecone as you can and keep in mind that this type of deployment can result in a delayed deployment. This is due to the time it can take for the chute to come out of the burrito. Do some research on the forum you will hear this delay issue many times, so plan for it by allowing a bit more altitude than you would with other deployment methods. If you have the field and the conditions are right, then for your cert flight play it safe and set it for 1,000.

Good luck and it is great to see someone doing something more than the bare minimum for their cert flight...most importantly, have fun!

Don't forget to pics some cert flight pics.

mpitfield said:

Don't forget to pics some cert flight pics.

Click to expand...

What he said ... sort of. :wink:

My old cutter tube got hosed, and in two weeks I'll be trying out a new one with my Leviathan. I had never thought about tying the e-match to the harness--that's a good idea. Fortunately, my Leviathan has survived two failed CC attempts without damage.

+1 on not having too much extra length in the wires to the cable cutter(s), just a modest amount of slack, such that pulling hard on the chute burrito in any direction doesn't put any stress on the wire. I no longer use the kevlar restraining strap to the cable cutter, it's just one more thing to get tangled - the MJG firewire initiators I use will *not* pull through the cap. I do make sure the initiator wire is secured at the NC, so it won't pull on the connections - A zip tie sounds like a great idea, though I've just done a couple wraps around the NC eyebolt.

Bat-mite said:

What he said ... sort of. :wink:

Click to expand...

inglish iz mi furst langwidge

ptrocketry said:

Hey!

I would recommend attaching the burrito with the zip tie *to* the shock cord that way it stays as a unit and cannot wrap around each other. I fly at NCR (live in Fort Collins) If you are close I'd be happy to meet up with you and go over recovery, or go over it at the launch site. I'd recommend going a bit higher on the main, I typically set it for 1000'. A long walk always beats a lawn dart.

Edward

Click to expand...

Hmm, I'd love to have some feedback at the launch site! I'll be launching with the Colorado School of Mines rocket club; there are a couple HPR-certified people in the group, but they've all done either single-deploy or conventional DD, so it would be nice to talk to someone with experience using the Cable Cutter.

By "attach with zip tie" you mean run the main shock cord through the same zip-tie that goes through the cable cutter, right? It also sounded like people are suggesting using additional zip ties to secure the e-match leads. The nose cone has a nice long kevlar loop, so it should be fairly easy to loop the leads around that a couple times as well.

Also, I'm using a kevlar shock cord with a cardboard tube, so I'd like some zipper insurance. Would wrapping the part of the shock cord that contacts the tube lip in several layers of masking tape work? How about duct tape?

Yes, I would say attached the with the same zip tie that goes through the cable cutter. You can use masking tape/electrical tap to hold the e-match to the shock cord - no need for anything fancy.

The best zipper insurance is to make sure everything is vertical before the parachute opens. A small streamer on your nosecone/burrito would put everything in the right orientation. I (knock on wood) have never had zipppers from nominal recovery. I use 3/8 and 1/2" kevlar with all types of body tubes. The only zipper I've had was on a filament wound fiberglass airframe and the altimeter deployed while going 500 mph @ 20k feet. Ruined that rocket and took 7 days to find.

Edward

Also - Oktoberfest is cancelled - the next chance will be in November for NCR.

Update:

On Tuesday I ground-tested everything. The apogee charge was pretty much perfect with 1.2 grams of 4F black powder, severing both shear pins and sending the nose and chute bundle skidding through the grass until the 15 ft shock cord was mostly straight.

The cable cutter didn't go so well. I assembled the device as per instructions, using one of the included cable ties and filling the included black powder scoop up to the first line. I pressed the e-match leads to the terminals of an 18V DeWalt drill battery (club's standard ground-testing procedure), and... nothing. After waiting a minute, I disassembled the Cable Cutter. The e-match appeared to have burned, and the black powder was gone, but the cable tie was intact.

There was no noticeable sound or smoke when firing the CC, which I would have expected.

Also, going back through the video of the apogee charge test, I noticed that after the main charge fired, there were a couple sparks from the noise cone and a faint "pop." My speculation is that the cable cutter was somehow set off during the apogee charge firing. But this was still much less than I've seen in videos of cable cutter ground testing, and I would have expected the cable cutter to sever the tie anyway.

Has anyone else ever had a cable cutter set off by a nearby charge? How could this be prevented in the future? Also, any ideas as to why the charge might have failed to sever the cable tie apart from "not enough BP"?

Clusterphiliac said:

Also, any ideas as to why the charge might have failed to sever the cable tie apart from "not enough BP"?

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Assuming the piston in the cable cutter is new it should cut, however the aluminum one does get blunt quickly and if it gets blunt enough it will fail to cut. This is why I switched to the stainless ones. The only other thing I can think of is the o-ring on the e-match allowed some BP to escape either after or during assembly so there was not enough BP left to ignite

My advice, forget this whole process until after cert. But that's me. I understand wanting to push the envelope with new technology and stuff but do that AFTER your cert. Irregardless of my opinion, good luck.

Listen to Jim for he is wise.
Don't try new stuff on cert day, sort it out afterwards.
Especially cable cutters as many have a love-hate relationship with them!

Here's an annotated picture of my typical cutter configuration. It uses a hot wire cutter but would be the same for a powder based cutter. I use a dedicated cord to hold the burrito, make sure there's plenty of slack in the wire, and attach everything to the quick link. This is a light rocket (3.5 lbs) so the thinner yellow Kevlar cord is more than strong enough and saves a little space.

I use a very similar setup to Matt - I've had 1 failure in 9 flights when the charge went off but the cable was not cut - I'm looking at the piston as the failure point.

It is important to make sure that the powder is contained and doesn't leak out. When the cutter goes off it is a very loud crack. I'm prototyping a version that cuts 0.180" zip ties and it uses a plastic piston for testing. It shears the cable everytime. How are you sealing the screw cap/e-match connection?

Edward

I use the archetype cable cutter and the standard o-ring around the starter as per the instructions. I was mentioning the 1 in 9 as a reference to the fact that it's pretty reliable.

It's possible that some BP leaked during the 12K ft descent but I flew another cable cutter that day setup the same way down from 35K ft apogee and it worked perfectly so I don't think BP leakage is likely.

ptrocketry said:

It is important to make sure that the powder is contained and doesn't leak out. When the cutter goes off it is a very loud crack. I'm prototyping a version that cuts 0.180" zip ties and it uses a plastic piston for testing. It shears the cable everytime. How are you sealing the screw cap/e-match connection?

Edward

Click to expand...

I think I may have identified the problem. I assembled the cutter based on this video: [video=youtube;qjIDk5Z6WIA]https://www.youtube.com/watch?v=qjIDk5Z6WIA[/video] which does not show the use of an O-ring over the e-match head. I'm guessing when the apogee charge fired, the high acceleration experienced by the chute bundle caused the black powder to fall out of the cable cutter, and some of it later ignited in open air, producing the sparks I saw. When I disassembled the rocket, some dark-colored powder fell out of the airframe. I assumed it was residue from the apogee charge, but now it seems like it must have been stray powder from the CC.

Also, does anyone happen to know the dimensions of the Cable Cutter piston? I'm pretty sure my unit has an aluminum piston, but I might be able to make one out of steel rod stock.

I have heard of some people buying extra caps and using hot glue to seal around the e-match wire to prevent the powder leaking out.

Perhaps I haven't had issues because I use 3F instead of 4F bp. The particles are very much larger, so I can't seen them leaking O-ring or not...pressure leaking would be another story though.

Regarding the cap, sometimes it initially does not thread all the way down. These times I back it off a little bit, tap the cutter on the table and finish tightening. With .11 g bp and an e-match there should be no threads showing when the cap is screwed on.

ONE VERY IMPORTANT THING: Clean the chamber and piston immediately after use. Powder build-up will eventually result in the piston not being able to move freely inside the chamber. On the range, you can probably use WD-40. If you wait too long, you'll need to soak it in acetone.

Bat-mite said:

ONE VERY IMPORTANT THING: Clean the chamber and piston immediately after use. Powder build-up will eventually result in the piston not being able to move freely inside the chamber. On the range, you can probably use WD-40. If you wait too long, you'll need to soak it in acetone.

Click to expand...

This test was the first time that this cutter had been used, but I'll keep that in mind for the future.

Fortunately, the club has plenty of acetone, so soaking the cutter overnight won't be a big deal.

This week I plan on testing again, but actually using an O-ring over the e-match. If that doesn't work, is there some sort of sticky substance that could be used as a seal, but then cleaned off the cap with common workshop solvents such as acetone and rubbing alcohol?

Clusterphiliac said:

This test was the first time that this cutter had been used, but I'll keep that in mind for the future.

Fortunately, the club has plenty of acetone, so soaking the cutter overnight won't be a big deal.

This week I plan on testing again, but actually using an O-ring over the e-match. If that doesn't work, is there some sort of sticky substance that could be used as a seal, but then cleaned off the cap with common workshop solvents such as acetone and rubbing alcohol?

Click to expand...

Hot water is all that's necessary to clean up BP residue, vinegar and water will do the same job in the field along with a nylon rifle/pistol bore brush.

As posted earlier hot glue can be injected around the ematch wire and pried out after use, and there will be no leakage of powder, poster tack could possibly be used around the wire to instead (we have a flier who uses it to seal the holes in the AV-Bay bulkhead that the ejection igniter wires pass through.

Dental wax works very well for sealing the screw cap and e-match.

Edward

ptrocketry said:

Dental wax works very well for sealing the screw cap and e-match.

Edward

Click to expand...

Thats good to know!

Clusterphiliac said:

Update:

On Tuesday I ground-tested everything. The apogee charge was pretty much perfect with 1.2 grams of 4F black powder, severing both shear pins and sending the nose and chute bundle skidding through the grass until the 15 ft shock cord was mostly straight.

The cable cutter didn't go so well. I assembled the device as per instructions, using one of the included cable ties and filling the included black powder scoop up to the first line. I pressed the e-match leads to the terminals of an 18V DeWalt drill battery (club's standard ground-testing procedure), and... nothing. After waiting a minute, I disassembled the Cable Cutter. The e-match appeared to have burned, and the black powder was gone, but the cable tie was intact.

There was no noticeable sound or smoke when firing the CC, which I would have expected.

Also, going back through the video of the apogee charge test, I noticed that after the main charge fired, there were a couple sparks from the noise cone and a faint "pop." My speculation is that the cable cutter was somehow set off during the apogee charge firing. But this was still much less than I've seen in videos of cable cutter ground testing, and I would have expected the cable cutter to sever the tie anyway.

Has anyone else ever had a cable cutter set off by a nearby charge? How could this be prevented in the future? Also, any ideas as to why the charge might have failed to sever the cable tie apart from "not enough BP"?

Click to expand...

I have never once had an Archetype cut the tie with the recommended 0.1g, and never seen it fail with 0.2g though that seems too much. I try for 0.15g but that can be tough to measure. Also I skip the ignitor o ring and hot glue that area to prevent leakage.

I'll check tonight, but I believe the vials are by volume, not mass.

Edward

ptrocketry said:

I'll check tonight, but I believe the vials are by volume, not mass.

Edward

Click to expand...

The vials are by volume.

Sorry if I got a detail wrong. The point was they do not sever for me using the recommended amount, and doubling guarantees severing but seems tough on the unit, so I go for 150%.

I believe I have aluminum pins. If I start using these again I will probably upgrade to steel ones, though I am not sure it will be worth it for me.