First Dual Deploy Questions

[Hnefi]

Thinking about my next project after I hung my stretched Leviathan on top of a nice grove of trees last weekend, and I have been wanting to learn how to properly dual deploy. For me, the fun in rocketry has been trying to learn a new "Technique" with each build... First it was filling balsa using CWF, then it was a simple two stage black powder, then it was a real paint job with primer & wet sanding, and most recently it was MPR construction with TTW fins, baffles, kevlar cord tied to MMT, etc etc... There's so much to learn at each stage and I don't want to just fly bigger and bigger and bigger motors until I hit the limits of what's attainable on my time and budget. I've done the standard progression from E2X kits on A/B, up to my first 'E' motor in a Vagabond, and recently some scratch built rockets designed for F's and G's... The club that is local to me only flies LPR and MPR, and since I don't have the resources to get down to NY/Potter like a lot of Canadians do for high power, I've been wanting to try to push altitude boundaries on the MPR propellant limit... That's what ultimately led me to putting a modded Leviathan up on a longburn CTI G54 RL, simmed to 2100'. Tracked it all the way with an arrow straight boost, but it was realistically way too high for the wind conditions that day.... My mistake, learned the hard way with losing my first CTI case.

So here's what I have been thinking.... I am likely going to build a DX3 and modify it for DD, since it has a fair sized payload tube with 1 bulkhead already in the kit. Do you think it's fair to just go drogueless for a kit this small and throw a sheet of mylar in there for visibility? I was thinking that if I convert the payload tube into an ebay, I will need some other setup than what I have seen on many of the HP build threads where you have a switch band with tubes butting up on both sides of it.... My first thought was to just buy or make a bulkhead on the other side of the payload tube, but then I would have to cut the NC shoulder for a bulkhead as well, and drill holes for shear pins. Also, the payload tube according to Madcow's supplied rocksim file is 10.5" long, which is super big for an ebay that I would likely only need a battery and simple Eggtimer Quark or something. I think it would make the most sense logically to put the ebay in the coupler (which is 5" long should be plenty of room based on some of the ebay setups I've read about), and then house the drogue/streamer/upper deployment in that payload tube. Thoughts on where the best place to house the ebay?

Secondly, I have a question about allthread. Most ebays I see here use a length of allthread that runs right through... Might be a stupid question but how do you secure the sled to the allthreads??? I am assuming just sand the allthread flat on one side and epoxy it? I don't have a belt sander or machine tools so I am thinking I might try to use angle brackets to screw the sled to instead of grinding down a steel piece of allthread flat on one side, is that considered safe and acceptable?

Thirdly, I've been reading that a lot of small DD projects just use glove fingertips or some disposable plastic for charge containment... Insert ematch, tape up, and fly. I then would basically just set the ematch leads into the eggtimer the night before at home, using a bit of bluetack to seal the holes in the bulkheads. The question is this: what are the white wiring terminals I often see on the outside of ebays?? For example, photo #3 in this post from conman's jr L1 build: https://www.rocketryforum.com/showthread.php?60950-Super-Dx3-Junior-level-1-Cert&p=671963#post671963
I'm assuming those are screw terminals so that the ematches just go into those rather than having to disassemble the ebay to hook up to the altimeter itself?
I have done a decent amount of soldering before with through-hole components, so I am thinking that making the jump to SMT won't be too bad.

Finally, I'm thinking about ground testing. For me this is ESSENTIAL since I don't want to put cases & more expensive rockets at huge risks anymore... Do you just ground test the drogue deploy by using a shopvac or something like that to drop the pressure by the vent hole, and assume the main works fine after that?

Thanks for reading this long smorgasbord of questions from a noob. Appreciate this forum a ton because of the amount of help you can get from very experienced rocketeers.

 

[les]

Best bet would be to get to a club launch and watch others and ask questions

Many DD have the booster, AV bay in the coupler, and payload section where the main chute is.

You don't need a switch band - you can mount a switch behind the vent hole that is needed for the altimeter and reach in with a screwdriver (or other tool) to activate (depending on your switch type). Some people just pass the wires out through the vent hole and will twist and tape them together and then push them back into the vent hole. The issue with this approach is if you run into an issue it is difficult to access the wires the disarm. Or you could use a magnetic switch such as sold by featherweight https://www.featherweightaltimeters.com/Av-Bay_Components.phpor the remote switch by eggtimer https://eggtimerrocketry.com/page48.php

Make the coupler into the AV bay - you will need bulkheads for both ends to keep the gasses from the ejection charge from damaging the electronics.

You can go drogueless, use a small chute, or a streamer. Depending on the height/timing some people leave the motor eject in as a backup. I often do this with the motor eject set to be a bit long so the electronics can do their job first. The nose should be held on with shear pins (#2 nylon screws work great). The main charge should blow the cone off and the chute out of the payload section.

There are different ways to secure the sled to the all thread - clamps, or glue a length of tubing to the sled that the all-thread can fit through, Then just slide the tubing over the thread. You can use some nuts to tighten on both ends if you have more all-thread than tubing. My sled uses angle brackets on each corner that the all thread can fit through.

It is not recommended to hook up the charges until you are at the field - you don't want to risk an accidental activation - imagine a boom in you car.....
You do need to seal the holes that the wires go through - you can use some modeling clay.

You are correct. The white terminals are to make connecting the charges easier so you do not need to disassemble the bay.

For ground testing you are trying to make sure you have the right amount of powder. Most people just run a pair of wires through the vent hole and then to the charge. You can use an Estes style controller (or just touch the wires to a suitable battery). Just make sure the rocket is somewhat secure and you have appropriate clearance for the flying parts. You run the ejection test with the full load of laundry (chute, shock cord, shear pins, etc). Depending on the amount of powder used the ejection system may throw things the full length of your cord so again make sure you have a safe place and no one in front/rear of the rocket during the test

Good luck - I am sure other will chime in

 

[blackbrandt]

OK.... let me try and answer these one at a time. See below.

Thinking about my next project after I hung my stretched Leviathan on top of a nice grove of trees last weekend, and I have been wanting to learn how to properly dual deploy. For me, the fun in rocketry has been trying to learn a new "Technique" with each build... First it was filling balsa using CWF, then it was a simple two stage black powder, then it was a real paint job with primer & wet sanding, and most recently it was MPR construction with TTW fins, baffles, kevlar cord tied to MMT, etc etc... There's so much to learn at each stage and I don't want to just fly bigger and bigger and bigger motors until I hit the limits of what's attainable on my time and budget. I've done the standard progression from E2X kits on A/B, up to my first 'E' motor in a Vagabond, and recently some scratch built rockets designed for F's and G's... The club that is local to me only flies LPR and MPR, and since I don't have the resources to get down to NY/Potter like a lot of Canadians do for high power, I've been wanting to try to push altitude boundaries on the MPR propellant limit... That's what ultimately led me to putting a modded Leviathan up on a longburn CTI G54 RL, simmed to 2100'. Tracked it all the way with an arrow straight boost, but it was realistically way too high for the wind conditions that day.... My mistake, learned the hard way with losing my first CTI case.

That's painful. Trust me... DD is worth it. Saved my butt on a few rockets.

So here's what I have been thinking.... I am likely going to build a DX3 and modify it for DD, since it has a fair sized payload tube with 1 bulkhead already in the kit. Do you think it's fair to just go drogueless for a kit this small and throw a sheet of mylar in there for visibility?

Drogueless or a streamer. I normally go with a streamer for visibility. The only purpose of a drogue is to stabilize the rocket (keep the part of the rocket with the main parachute above the fin can, so they don't get tangled when the parachute deploys) and slow it slightly.

I was thinking that if I convert the payload tube into an ebay, I will need some other setup than what I have seen on many of the HP build threads where you have a switch band with tubes butting up on both sides of it.... My first thought was to just buy or make a bulkhead on the other side of the payload tube, but then I would have to cut the NC shoulder for a bulkhead as well, and drill holes for shear pins. Also, the payload tube according to Madcow's supplied rocksim file is 10.5" long, which is super big for an ebay that I would likely only need a battery and simple Eggtimer Quark or something. I think it would make the most sense logically to put the ebay in the coupler (which is 5" long should be plenty of room based on some of the ebay setups I've read about), and then house the drogue/streamer/upper deployment in that payload tube. Thoughts on where the best place to house the ebay?

If I'm picturing it right.... that sounds like a decent idea. As long as you can access both ends of the bay for your ejection charge setup, you will be fine.

Secondly, I have a question about allthread. Most ebays I see here use a length of allthread that runs right through... Might be a stupid question but how do you secure the sled to the allthreads??? I am assuming just sand the allthread flat on one side and epoxy it? I don't have a belt sander or machine tools so I am thinking I might try to use angle brackets to screw the sled to instead of grinding down a steel piece of allthread flat on one side, is that considered safe and acceptable?

Normally, most people glue a piece of launch lug to the sled and slide that over the allthread. Other people (like me) just cut their sled exactly to the size of the inside of the bay so it can just be snug fit into the bay. Leaves you plenty of room for other altimeters and stuff.

Thirdly, I've been reading that a lot of small DD projects just use glove fingertips or some disposable plastic for charge containment... Insert ematch, tape up, and fly. I then would basically just set the ematch leads into the eggtimer the night before at home, using a bit of bluetack to seal the holes in the bulkheads. The question is this: what are the white wiring terminals I often see on the outside of ebays?? For example, photo #3 in this post from conman's jr L1 build: https://www.rocketryforum.com/showthread.php?60950-Super-Dx3-Junior-level-1-Cert&p=671963#post671963
I'm assuming those are screw terminals so that the ematches just go into those rather than having to disassemble the ebay to hook up to the altimeter itself?
I have done a decent amount of soldering before with through-hole components, so I am thinking that making the jump to SMT won't be too bad.

Yes, those are terminal blocks. You can run a wire from your altimeter to the terminal block, and then every flight only have to put a new ematch on the terminal block without having to take apart your bay. Again, matter of opinion. I tend to run my ematches directly to my altimeter through a hole in the bulkhead (a) because it saves real estate on the bulkhead and (b) because it is another place that I remove a failure point. However, some people like the terminal blocks because the quickened turnaround time for flight. However, because I only have a few altimeters, I have to take apart my bay after every flight, so it doesn't save much time for me.

Finally, I'm thinking about ground testing. For me this is ESSENTIAL since I don't want to put cases & more expensive rockets at huge risks anymore... Do you just ground test the drogue deploy by using a shopvac or something like that to drop the pressure by the vent hole, and assume the main works fine after that?

Ground testing is a 2 part process. The first part is testing your altimeter itself. Look up vacuum chambers on the forum. All they are is a big syringe, some surgical tubing, and an airtight container. You put the altimeter, battery, and your ematches into the cup (run the ematch heads out of the container to prevent damage to the altimeter), turn on your altimeter, and pull on the syringe. This will simulate a flight, and you watch to make sure both ematches fire.

The second part of ground testing is the charge testing. Some altimeters have wired ground testing capabilities, but I tend to simply run a wire through the vent hole in the altimeter bay to the charge well. Use a black powder calculator to figure out about how much powder you'll need. Pack the charge, and hook up an ematch to it, and hook the ematch up to some wires about 15 feet long. Pack up your rocket as you would have it for flight, with parachutes, shock cord, nomex/wadding, sheer pins, and everything else. If you love your paint job because you're one of those painting gods who seems to get an immaculate paint job just by looking at your rocket, put a few towels on the ground in order to protect it. I tend to ground test before painting though.

Bring your wires back about 15 feet, and touch them to the terminals on a battery to fire off the charge. You are looking for the nose cone to pull completely away from the rocket, and have the parachute (for main) come completely out of the rocket. For the drogue, you are looking for the rocket to simply separate without too much stress, or else you risk the shock forcing the main parachute out as well... which kinda defeats the purpose of DD. Do a search on TRF and you'll find how people do their ground tests.

Thanks for reading this long smorgasbord of questions from a noob. Appreciate this forum a ton because of the amount of help you can get from very experienced rocketeers.

Love the word smorgasbord. Remember... we were all here at one point and we all have to learn.

 

[timro]

So since blackbrant did a good job of addressing most of the questions, you might be asking where you could find a build like this (29mm DX3 with Dual Deploy)

Here's one:

https://www.rocketryforum.com/showthread.php?51515-Madcow-DX3-build

Dual Deploy stuff starts at post #25. This was my first dual deploy setup and I used motor deploy for apogee with a small drogue and the Adept DDC2 for the main deployment. Flew it across a lot of motors in the G-H class before a G53 cato did it in.

For what you are doing streamer or small drogue will help with visibility. For this setup, I was using the Madcow 2.6" bay with a single central allthread. Since I used motor deployment for drogue, I wasn't bothered by having to screw in the aft bulkhead with eyebolt.

For the next DD build of this weight category (<1000g), I used 2 #8-32 allthread bolts for securing the bulkheads, with wing-nuts to make securing things tool-less and easy. Still flying that one (Madcow Striker) on any 29mm motor I can fit into it.

 

[Banzai88]

Look into the Mad Cow Torrent from Apogee. Similar to the DX3 you're wanting, and already all set up for single or DD. Also, AMAZING set of "Build your first DD rocket" videos.

 

[watermelonman]

I made my Leviathan dual deploy from the start. I was not happy with charges fighting shear pins in that material at all. For the traditional configuration I recommend much, much stronger tubing.

 

[Zeus-cat]

You need a switch inside your altimeter bay too. You need to be able to turn the altimeter on and off without opening the rocket up. A cheap and dirty method is to have two wires hanging out of your rocket so that twisting them together arms the altimeter. Then you tape the wires to the OUTSIDE of the rocket. The wires must be outside so that you can disarm the altimeter if you have a problem. If you use a switch it must be securely mounted to the altimeter sled.

I always recommend that you separate the battery from the altimeter so that a loose battery does not destroy your altimeter. I've seen that happen. We had a college team come to a club launch and they just taped the 9V battery in place. No one from our club checked their altimeter sled before launch so we didn't know that they had did that. We did a thorough examination of the exterior of the rocket and parts of the recovery system prior to launch. Anyway, their dual deploy setup failed to work properly and after the rocket crashed we saw the battery had come loose and bounced around inside the bay. Nasty stuff.

I built a K and S Arctic Wolf and they have a beautiful sled for that rocket. Here is a photo of their altimeter sled design. You'll notice that the allthread runs through bulkheads on the sled instead of tubes. This is hard to make on your own if you don't have decent woodworking tools and skills. I think they used to sell these bays by themselves.

 

[Hnefi]

Wow, so much good stuff here.... I'll try to reply to everyone.

Best bet would be to get to a club launch and watch others and ask questions

Many DD have the booster, AV bay in the coupler, and payload section where the main chute is.

You don't need a switch band - you can mount a switch behind the vent hole that is needed for the altimeter and reach in with a screwdriver (or other tool) to activate (depending on your switch type). Some people just pass the wires out through the vent hole and will twist and tape them together and then push them back into the vent hole. The issue with this approach is if you run into an issue it is difficult to access the wires the disarm. Or you could use a magnetic switch such as sold by featherweight https://www.featherweightaltimeters.com/Av-Bay_Components.phpor the remote switch by eggtimer https://eggtimerrocketry.com/page48.php

Make the coupler into the AV bay - you will need bulkheads for both ends to keep the gasses from the ejection charge from damaging the electronics.

You can go drogueless, use a small chute, or a streamer. Depending on the height/timing some people leave the motor eject in as a backup. I often do this with the motor eject set to be a bit long so the electronics can do their job first. The nose should be held on with shear pins (#2 nylon screws work great). The main charge should blow the cone off and the chute out of the payload section.

There are different ways to secure the sled to the all thread - clamps, or glue a length of tubing to the sled that the all-thread can fit through, Then just slide the tubing over the thread. You can use some nuts to tighten on both ends if you have more all-thread than tubing. My sled uses angle brackets on each corner that the all thread can fit through.

It is not recommended to hook up the charges until you are at the field - you don't want to risk an accidental activation - imagine a boom in you car.....
You do need to seal the holes that the wires go through - you can use some modeling clay.

You are correct. The white terminals are to make connecting the charges easier so you do not need to disassemble the bay.

For ground testing you are trying to make sure you have the right amount of powder. Most people just run a pair of wires through the vent hole and then to the charge. You can use an Estes style controller (or just touch the wires to a suitable battery). Just make sure the rocket is somewhat secure and you have appropriate clearance for the flying parts. You run the ejection test with the full load of laundry (chute, shock cord, shear pins, etc). Depending on the amount of powder used the ejection system may throw things the full length of your cord so again make sure you have a safe place and no one in front/rear of the rocket during the test

Good luck - I am sure other will chime in

I think that I am going to take a step back and go slow with my journey into electronics. Since I have never built one of these from the ground up, I have decided that I'm going to first make a basic kit and modify it just to carry an altimeter. That will give me good experience on measuring parts as well as soldering together a kit, and I can then take it to the next level by making that same kit deploy the main at apogee with that altimeter.

This also lets me take my first build or two to club launches and get feedback.

Look into the Mad Cow Torrent from Apogee. Similar to the DX3 you're wanting, and already all set up for single or DD. Also, AMAZING set of "Build your first DD rocket" videos.

This is a great suggestion. My supplier doesn't stock the Torrent but I may just order one for the future.

In the interim, I am looking at building a Madcow Tembo and putting a basic altimeter bay in the nose cone as per John Coker's video. That rocket works well for me particularly because it's a 4" diameter rocket that would work well for your classic Low n' Slow flight, as the field I am launching at is not really big enough for H+ motors.

You need a switch inside your altimeter bay too. You need to be able to turn the altimeter on and off without opening the rocket up. A cheap and dirty method is to have two wires hanging out of your rocket so that twisting them together arms the altimeter. Then you tape the wires to the OUTSIDE of the rocket. The wires must be outside so that you can disarm the altimeter if you have a problem. If you use a switch it must be securely mounted to the altimeter sled.

I always recommend that you separate the battery from the altimeter so that a loose battery does not destroy your altimeter. I've seen that happen. We had a college team come to a club launch and they just taped the 9V battery in place. No one from our club checked their altimeter sled before launch so we didn't know that they had did that. We did a thorough examination of the exterior of the rocket and parts of the recovery system prior to launch. Anyway, their dual deploy setup failed to work properly and after the rocket crashed we saw the battery had come loose and bounced around inside the bay. Nasty stuff.

I built a K and S Arctic Wolf and they have a beautiful sled for that rocket. Here is a photo of their altimeter sled design. You'll notice that the allthread runs through bulkheads on the sled instead of tubes. This is hard to make on your own if you don't have decent woodworking tools and skills. I think they used to sell these bays by themselves.

That sounds like a brutal failure.... To do all of the work and have it destroyed by a loose battery. I always take my builds so slow and methodically (particularly during the finish stage), I would absolutely hate to crash one like that.

That is a great picture, thanks. I have zero woodworking experience and no power tools (I'm a grad student), so I think going full DD is a bit beyond my capabilities for the moment... But you never know what I might be able to get access to in the future.

A question for all of you guys - I am planning to order an Aeropack retainer (38mm) for the Tembo and adapt down to 29mm so I can use 2-3 grain CTI loads which are still small enough to be classified as non high power. However, there are 3 different diameters of retainer. On Madcow's webpage, I downloaded the rocksim file for the Tembo and it says that the OD of the MMT is 1.635", however Aeropack lists the correct retainer for Madcow tubes as the 38P which has a 1.65" diameter. Which one is the correct one??

Also, since that's such a short rocket there's not really much space to fit a baffle system in. Would it be enough to get a good sized Nomex blanket to protect the chute, or am I also going to need to stuff this thing with dog barf?

 

[watermelonman]

Wow, so much good stuff here.... I'll try to reply to everyone.


I think that I am going to take a step back and go slow with my journey into electronics. Since I have never built one of these from the ground up, I have decided that I'm going to first make a basic kit and modify it just to carry an altimeter. That will give me good experience on measuring parts as well as soldering together a kit, and I can then take it to the next level by making that same kit deploy the main at apogee with that altimeter.

This also lets me take my first build or two to club launches and get feedback.


This is a great suggestion. My supplier doesn't stock the Torrent but I may just order one for the future.

In the interim, I am looking at building a Madcow Tembo and putting a basic altimeter bay in the nose cone as per John Coker's video. That rocket works well for me particularly because it's a 4" diameter rocket that would work well for your classic Low n' Slow flight, as the field I am launching at is not really big enough for H+ motors.


That sounds like a brutal failure.... To do all of the work and have it destroyed by a loose battery. I always take my builds so slow and methodically (particularly during the finish stage), I would absolutely hate to crash one like that.

That is a great picture, thanks. I have zero woodworking experience and no power tools (I'm a grad student), so I think going full DD is a bit beyond my capabilities for the moment... But you never know what I might be able to get access to in the future.

A question for all of you guys - I am planning to order an Aeropack retainer (38mm) for the Tembo and adapt down to 29mm so I can use 2-3 grain CTI loads which are still small enough to be classified as non high power. However, there are 3 different diameters of retainer. On Madcow's webpage, I downloaded the rocksim file for the Tembo and it says that the OD of the MMT is 1.635", however Aeropack lists the correct retainer for Madcow tubes as the 38P which has a 1.65" diameter. Which one is the correct one??

Also, since that's such a short rocket there's not really much space to fit a baffle system in. Would it be enough to get a good sized Nomex blanket to protect the chute, or am I also going to need to stuff this thing with dog barf?

You should be more than fine with properly sized nomex. That is all I ever use now.

As for the rest of it, I definitely recommend stepping one by one into electronics. A favorite trick of mine is to send up second or even third full size parachute with electronic deployment, on flights low enough so that the whole show is visible. This way you have a parachute deployed by motor ejection like you are used to, but you can test out new deployment techniques without worry, and where you can see the results. As you get more comfortable, cut out the motor ejection, then eventually move that extra parachute down to drogue size or streamer, and you are there!

 

[HHaase]

I made my Leviathan dual deploy from the start. I was not happy with charges fighting shear pins in that material at all. For the traditional configuration I recommend much, much stronger tubing.

I was just trying to figure out a solution to that problem in my Scion. Definitely needs some kind of positive retention for the nose cone to the upper tube, but I'm not sure how the Estes tubing will survive the pin. I was considering a wrap or two of fiberglass on the external surface of the top inch of tubing.

-Hans

 

[Banzai88]

I was just trying to figure out a solution to that problem in my Scion. Definitely needs some kind of positive retention for the nose cone to the upper tube, but I'm not sure how the Estes tubing will survive the pin. I was considering a wrap or two of fiberglass on the external surface of the top inch of tubing.

-Hans

Brass shim material. Techniques for laminating it into the tubing abound. Agree that there is a HUGE difference in thickness and suitability with real HP tubes vs. Estes Pro Series tubes when doing advanced things with them. True HP tubes are so much thicker and stiffer and more durable, you'll notice a difference just picking them up!

 

[Handeman]

I haven't used DD on the thinner Estes tubes, but until I started with 6" fiberglass, I never used shear pins.

IMHO, for smaller rockets like the Estes Pro Series II, I would highly suggest you try friction fit. It has worked for a lot of people for a long time. If you can pick up the rocket by the nose cone and give it a firm shake without it coming apart, it should be good. If it slips apart slightly, that is probably better than a real tight fit. I've used this method successfully on rocket up to 4" diameter and 10 lbs.

I know shear pins are the "in" thing lately and they certainly have their place, but for small light rockets like the Estes Pro series, they may not be worth the trouble considering the issues involved.

Just MHO.

 

[cerving]

Friction fit for Estes tubes works fine. Save the shear pins for fiberglass or Blue Tube, where the rockets are bigger and heavier and you actually need them.

 

[grouch]

I have yet to use sheer pins. I prefer friction fit as I have been flying paper rockets.

 

[HHaase]

Had to add some nose weight to my scion, and have had issues with yanking the main out too. Might also try a longer recovery line on the dogue first before resorting to pins.

 

[KenRico]

I was just trying to figure out a solution to that problem in my Scion. Definitely needs some kind of positive retention for the nose cone to the upper tube, but I'm not sure how the Estes tubing will survive the pin. I was considering a wrap or two of fiberglass on the external surface of the top inch of tubing.

-Hans

I did a single wrap of Fiberglass on my daughters Mega Der Purple Max.. it boosted well under H400 vMax and with the H550 ST the tube did fine..although i had optimized the fins a little too much and they shredded.

they say i may have had some pressure seperation also ..some shear pins may have avoided that.

Kenny