Please QC my Cable Cutter Setup

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JimJarvis50

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I'm setting up for my first cable cutter attempt. Electronics are in the nose cone (upper right). The apogee charge goes down in the tube between the motor and the chute. Do I need to cover the cable cutter?

First trial flight (for cable cutter and rocket) will be a K940 to about 20K with main deployment high at 1,500 feet.

Any comments on my setup?

Jim

DSCF0690.jpg
 
In my set up, I have a charge canister and terminal block mounted on my nose cone bulkhead for my apogee deployment. I also use motor deploy as backup for apogee. I add a longer delay in case the one that comes with the reload isn't long enough. Your set up looks good from what I can see though. GEDC0024.jpg
 
Both setups look very clean.

I'm planning to start using the Cable Cutter as well. Can't tell for sure from the photos but I assume you are both venting the altimeter compartment with a hole or multiple holes in the nose cone. In Jim's photo the shoulder of the nose cone looks like it has a vent (too big for a shear pin I think) that will be lined up with a corresponding vent hole in the body tube, yes?

Edit: After reading TA's response to my question on the same subject in another thread, I have my answers. Thank you.

"These are not the droids you're looking for. Nothing to see here. Move along."
 
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Both setups look very clean.

I'm planning to start using the Cable Cutter as well. Can't tell for sure from the photos but I assume you are both venting the altimeter compartment with a hole or multiple holes in the nose cone. In Jim's photo the shoulder of the nose cone looks like it has a vent (too big for a shear pin I think) that will be lined up with a corresponding vent hole in the body tube, yes?

Edit: After reading TA's response to my question on the same subject in another thread, I have my answers. Thank you.

"These are not the droids you're looking for. Nothing to see here. Move along."

The vents are not easy to see in the picture. The more obvious hole in the airframe - several inches to the left - vents the airframe below the nose cone shoulder. This is necessary in this design because there is no tube break that might otherwise help with venting. If you look closely, there is a double hole further to the right on the tube. This is just above the reflection "line" and perhaps 1.5 inches below the top of the tube. One of the double holes is for a shear pin and the other is a vent into the cone. There are three sets. The large hole in the nose cone shoulder isn't a vent - it's for the hardware that holds the bulkhead on the cone.

One question i have about my setup is whether the chute should be connected to the harness between the cone and the tube. An alternate approach would be to have a separate section of kevlar, a foot or two long, connected to the cone and then the chute. Don't really know if this would help though.

Jim
 
One question i have about my setup is whether the chute should be connected to the harness between the cone and the tube. An alternate approach would be to have a separate section of kevlar, a foot or two long, connected to the cone and then the chute. Don't really know if this would help though.

Jim

Based on my unfortunate experience with the chute between the cone and the tube, I would 100% definitely have a separate leader for the main parachute.
 
My chute is connected directly to nose cone. I have used this method about 7-8 times now with no problems.
I'm not saying that my method is best but it's worked so far. I think gbjsky01 (Jeff) has quite a few more flights
than me using the cable cutter so I hope he chimes in here.
 
Hey Jim,

I've been flying this setup for years -- good choice. Only thing I see different in your setup is that I'll leave the match wire separate from the shock cord, so that the wire is not subject to the jerking around of the shock cord. I'll deliberately leave the match wire much longer than that portion of the shock cord so when the cord is tight, there is still plenty of slack in the wire so there's never any tension on it.

I'll also yank the zip tie super tight -- chute can slip out surprisingly easily, so I usually try and get there to be an hourglass shape so the chute physically can't slide out. Also, when the zip tie is super tight, there's more energy when the cable is cut, which helps everything deploy cleanly.

I assume this is for next weekend? See you then -- I'll be there with a single use motor poured into that 2.0" tubing Jay has. Hopefully we won't have to spend an entire afternoon looking for it this month.

Steve
 
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I'm also doing a first launch using the cable cutter, so I did a search here and found this thread. Great info. that I have incorporated into my setup.
Here is what I came up with:
005.jpg


This is in a RW "Lil Rascal" which might be hard to see at apogee, so I added a 25 ft. streamer to the drogue shock cord. Probably tape a tracker on there too. The Main is on a separate short piece of kevlar and the e-match wire is tied to the base of the eye-bolt. I'm gonna take Steve's advise and tighten down the zip tie before flight. Here is a close-up of the bulkhead:
003.jpg


I used a .38 cartridge for the ejection charge holder and added an external beeper to the Eggtimer enclosed in the N/C. It's still hard to hear the beeps when it's all closed up though. Any comments or suggestions would be appreciated.

One problem I had was getting the e-match lead to fit through the cap on the cable cutter. I tried CJ's "lighters" first, and then a J-tec. Both gave me some grief. Anybody have a tip on how to get them through the tiny hole in the cap?
 
I'm also doing a first launch using the cable cutter, so I did a search here and found this thread. Great info. that I have incorporated into my setup.
Here is what I came up with:
005.jpg


This is in a RW "Lil Rascal" which might be hard to see at apogee, so I added a 25 ft. streamer to the drogue shock cord. Probably tape a tracker on there too. The Main is on a separate short piece of kevlar and the e-match wire is tied to the base of the eye-bolt. I'm gonna take Steve's advise and tighten down the zip tie before flight. Here is a close-up of the bulkhead:
003.jpg


I used a .38 cartridge for the ejection charge holder and added an external beeper to the Eggtimer enclosed in the N/C. It's still hard to hear the beeps when it's all closed up though. Any comments or suggestions would be appreciated.

One problem I had was getting the e-match lead to fit through the cap on the cable cutter. I tried CJ's "lighters" first, and then a J-tec. Both gave me some grief. Anybody have a tip on how to get them through the tiny hole in the cap?

What kind of cap? There is a smaller sort made for Q2G2's, and a larger size one for the e-match shooter's wire.
 
What kind of cap? There is a smaller sort made for Q2G2's, and a larger size one for the e-match shooter's wire.

Good call, Sharon ordered these last year when they had a sale. I checked the paperwork and it does say they are for the Q2G2's which aren't available. I will make another order and pick up the right stuff.
 
What kind of cap? There is a smaller sort made for Q2G2's, and a larger size one for the e-match shooter's wire.

Good catch. I was wondering why I didn't have a problem with that. Per the discussion, I'm going to use a separate piece of harness, get it mounted a bit closer to the cone, and crank down on the tie.

Yes, this one is for next week. First test flight on the rocket. A K940 on a 2 pound rocket should be fun. Although the search last time took a while, I got some very valuable tracking information from it (which I still need to confirm this next time).

Jim
 
Good catch. I was wondering why I didn't have a problem with that. Per the discussion, I'm going to use a separate piece of harness, get it mounted a bit closer to the cone, and crank down on the tie.

Yes, this one is for next week. First test flight on the rocket. A K940 on a 2 pound rocket should be fun. Although the search last time took a while, I got some very valuable tracking information from it (which I still need to confirm this next time).

Jim

Jim,

Glad to hear you're going to implement some of my suggestions, hopefully it saves you some trouble.

I was referring to the all afternoon we spent finding my rocket last month -- aiming for no repeats of that!

Steve
 
Gotta hand it to Archetype Rocketry, their webpage is a breeze to navigate and the prices are excellent. Picked up two caps, two of the new stainless steel pistons, 25 o-rings and 25 wire ties, all shipped flat rate for $25.25. Took about 5 minutes.
 
I use a quick link to connect the chute bridle right to the nose. This set up works awesome and has turned into my favorite dual deploy method. I find the single break, reefed chute method easier and quicker to prep. Also, it just looks sexier.

DSC_0005-M.jpg
 
It's a little more awkward in zipperless configuration, though. My attempt to force it into zipperless duty caused me my issues.
 
No Drogue?

With the cable cutter or somewhere else? This rocket doesn't have any tube breaks except at the cone. I was wondering about the feasibility of having a small drogue chute, but with the likelyhood of high speed deployment, I figured that would just cause problems.

Jim
 
Hi Jim,

I'm building a 7.5" diameter squat rocket with a 29" fiberglass NC, a 38" sustainer, with a plan to DD in the future. I'm trying to avoid lengthening the BT by adding a cargo bay for the electronics. I would like to locate the av-bay in the nose cone and use a cable cutter for the main. In planning the build I've run into a couple of issues, static ports located on or near the nose cone are not recommended for a barometer based altimeter and were to locate the av-bay switch. What altimeter are you using and were did you mount the switch? Any clearer photos of static ports and switch location?

Are you using motor ejection for the streamer/drogue deployment? What's the purpose of the second ematch, were is the charge attached?

Spicer
 
Spicer
We do it all the time, putting static ports in the nose cone shoulder. No problems yet. I am using a Perfect Flight Stratologger.
 
In planning the build I've run into a couple of issues, static ports located on or near the nose cone are not recommended for a barometer based altimeter and were to locate the av-bay switch. What altimeter are you using and were did you mount the switch? Any clearer photos of static ports and switch location?

Are you using motor ejection for the streamer/drogue deployment? What's the purpose of the second ematch, were is the charge attached?

Spicer

You've raised several good questions. I can give you some answers for this specific rocket. They may or may not apply for yours.

Static ports near the cone aren't ideal. However, there are two things to consider. First, at the points in the flight where you need good data (i.e., at apogee and at low altitude deployment), the rocket isn't traveling very fast. At those times, the altimeter is producing good data. Second, some altimeters have ways of avoiding getting spoofed during portions of the flight where the altimeter data might not be accurate. The MAWD, for example, has an explicit mach delay, and the quality of the altitude data during that delay doesn't matter. For this rocket, I will be using a stratologger because the altitude is above the capability of the MAWD. My understanding is that the stratologger will be calculating what is essentially a smoothed velocity value from the altitude data. I'm reasonably confident that the altimeter will be able to figure out its going really fast early on, and not deploy an apogee charge until apogee is actually achieved.

The photos below show the current setup. The first pic just shows the overall layout. The cone is off so that you can see the altimeter skid. There will be a beeline tracker skid there as well. I have modified the setup so that the chute is on its own short piece of harness. The apogee charge (in the "masking tape" container) sits just above the motor and then the bulk of the harness length goes on top of that.

This rocket is designed to fly over 30K feet on motors such as the L935 or K300. It's not possible to use motor ejection (the delay is not nearly long enough). The apogee charge is electronic and just happens to sit about where the motor ejection charge would have been.

The second pic shows things after packing the separation charge and the harness. This picture more clearly shows the position of the screw switch at the base of the cone (its an Aerocon PVC screw switch). At the pad, the switch is turned on and the cone is set into place. Once continuity is verified, the shear pins are inserted and the rocket is placed into the tower. I've used this approach on many 2" rockets. Note that the large hole in the side of the cone is for the hardware that holds the bulkhead in the cone. It's possible that apogee charge pressure could get into the cone through these openings and potentially trigger the "main" charge. Therefore, for the actual flight configuration, these openings are covered, as is the opening at the base of the cone where the ematch wires emerge.

The third photo shows the locations of the vents (six total, three into the tube below the cone and three into the cone shoulder). The vents on the left side of the picture vent the airframe section only. Then, there are three pairs of holes higher on the airframe that have matching holes in the cone shoulder. For each pair, one hole is a vent into the cone and the other is for a shear pin. The fourth pic is with the nose cone inserted. The cone is a nearly exact match in diameter with the top of the tube (which I hope help to avoid turbulence that might spoof the altimeter).

The last pic is a drawing of the rocket with the 6XL case. I'm probably going to need a smaller chute when using that case. There's not much room.

Jim

DSCF0694.jpg

DSCF0695.jpg

DSCF0697.jpg

Shocklet Mini Squared.jpg

DSCF0699.jpg
 
I looks good, you may want to add one loop or two more of wire for some added slack.


TA
 
I have had very good luck with my cable cutter. The only time it didn't work was when I didn't have enough slack and the wire splice was pulled apart.
 
Crossfire & Jim,

That's exactly what I wanted to know. I've been flying with Stratologger altimeters. Their instructions say, static port "holes should be far aware from the nose cone and shoulder", becuse of turbulence. Knowing other flyers have had good results locating the static ports on the NC shoulders, gives me more confidence to mount my av-bay in the NC.

Spicer
 
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I did my test flight over the weekend. Some good news and some not. This rocket has surface mounted fins with no tip to tip. The fins didn't fall off at Mach 2.2. Good news! Unfortunately, the apogee charge spit the motor. It was connected to the harness, so the rocket just came down quicker than it should have. There was no damage (good news), but no test of the cable cutter (bad news, although it did cut the tie cable).

Regarding the altimeter data (with vents near the nose cone), the attached plot shows the MAWD data against the simulation. The altitude data aren't very good until the speed drops to below about Mach 0.8. I'm not sure if the Stratologger would be capable of dealing with this data (i.e., not deploy at the point of the altitude inflection). It would probably be better to use an altimeter with an actual Mach lockout or an inertial altimeter.

Jim

Shocklet Mini Squared test data.jpg
 
I did my test flight over the weekend. Some good news and some not. This rocket has surface mounted fins with no tip to tip. The fins didn't fall off at Mach 2.2. Good news! Unfortunately, the apogee charge spit the motor. It was connected to the harness, so the rocket just came down quicker than it should have. There was no damage (good news), but no test of the cable cutter (bad news, although it did cut the tie cable).

Regarding the altimeter data (with vents near the nose cone), the attached plot shows the MAWD data against the simulation. The altitude data aren't very good until the speed drops to below about Mach 0.8. I'm not sure if the Stratologger would be capable of dealing with this data (i.e., not deploy at the point of the altitude inflection). It would probably be better to use an altimeter with an actual Mach lockout or an inertial altimeter.

Jim

I'm fairly certain that the Stratologger (or various other recent Kalman filtered altimeters like the RRC3, RRC2+, or the cheaper Altus Metrum offerings) wouldn't deploy erroneously, although your recorded data is still compromised.
 
I did my test flight over the weekend. Some good news and some not. This rocket has surface mounted fins with no tip to tip. The fins didn't fall off at Mach 2.2. Good news! Unfortunately, the apogee charge spit the motor. It was connected to the harness, so the rocket just came down quicker than it should have. There was no damage (good news), but no test of the cable cutter (bad news, although it did cut the tie cable).

Regarding the altimeter data (with vents near the nose cone), the attached plot shows the MAWD data against the simulation. The altitude data aren't very good until the speed drops to below about Mach 0.8. I'm not sure if the Stratologger would be capable of dealing with this data (i.e., not deploy at the point of the altitude inflection). It would probably be better to use an altimeter with an actual Mach lockout or an inertial altimeter.

Jim
It looks like the altimeter detected apogee at 28 seconds and fired the pyro circuit. The StratoLogger runs a Kalman filter and will not deploy at Mach transients, and it worked.

Bob
 
Bob, just to clarify, the flight was done with a MAWD with a preset Mach lockout. The Stratologger comes into the picture on future launches where the expected altitude (30K) is above the capability of the MAWD (as I recall, the limit for the MAWD is around 25K, but that's from memory). I could use a Stratologger, but this would be with the calculated Mach lockout. I have an RRC2, which has a preset Mach inhibit and 40K MSL. I'll likely just use that, although I'm still curious if the Stratologger could handle it.

Jim
 
I know this is an old thread but just purchased a cable cutter and have a question. I see on a few of the images here that the apogee charge is near the cable cutter wire. Has anyone had any burn through with the cable cutter wire from the apogee charge thus shorting the cable cutter wires?
 
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