Electronic recovery andDual Deployment

Discussion on ground control/GSE and recovery equipment. This includes launch pads, triggers, chutes, streamers etc. Includes other items such as simulation and other computer software, etc.

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Lamp
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Electronic recovery andDual Deployment

Postby Lamp » Sat Jan 19, 2013 7:06 pm

I have started this thread to try to explain the nuts and bolts of electronic recovery and dual deployment for those that have not yet tried it. We all have different ideas on what works and I am sure others will want to have their say, I would welcome your input! :wink:

Firstly, what is electronic deployment? It is the use of electronic timers and altimeters to initiate the pyrotechnic charges to deploy the recovery system. I have never used timers but there are various commercial systems available like the Aerotech EFC system, the Missileworks PET2 timer the PML Accu-fire timer and others. Those that are proficient in electronics can probably build one from circuit diagrams or design and build one from scratch. This post will be about the use of altimeters which is what I have had experience with.

Electronic deployment can be used either for the ejection of a single main parachute in the same way as motor deployment, or for dual deployment.

Dual deployment is used to deploy the main chute at an altitude closer to the ground than apogee which will decrease the drift of the rocket, especially with higher altitude flights and on windy days. The first pyrotechnic charge causes the rocket to break apart at apogee which makes the rocket unstable and prevents it from returning in a high speed ballistic arc. The apogee deployment should slow the decent of the rocket sufficiently so that the main chute can be safely deployed without being shredded. The apogee deployment can use either just a long shock chord (Drogueless recovery), a streamer or a small parachute to achieve this. If you use drogueless recovery you should have a good estimation of the decent velocity you will achieve to make sure it will be safe.

Here is my Competitor 3 just after the apogee deployment pyro has fired and the streamer has just started to deploy.
Image

When the rocket has fallen to a pre-determined altitude, the altimeter will initiate a second pyro charge which deploys the main chute slowing the decent further for a safe recovery.

Here is my 4" Dark star under main. The drouge chute was deployed at apogee and is the small one at the bottom, the main chute was programmed to be deployed at 700'
Image
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Re: Electronic recovery andDual Deployment

Postby Lamp » Sat Jan 19, 2013 7:34 pm

There are various commercial altimeters available and it is personal preference really as to which one(s) you should use.

Here are a few different altimeters. From left to right they are A telemetrum, A Perfectflight Stratologger, A G-Wiz HCX and a Missile works RRC2 mini.
Image

Altimeters need three things. They need a power supply, they need to be at atmospheric pressure at the altitude they are at and they need to be protected, both from mechanical damage and from the pressure and residue caused by the pyrotechnic charges they initiate. The power requirements will be specified in the manual but typically a 9v battery will be OK although this is not always the case. The typical way altimeters for dual deployment are protected is to put them into an avionics bay built between the main body tube (containing the first shock chord and drogue chute) and the payload bay (containing the second shock chord and main chute). The way they can be at atmospheric pressure is to put vents into the Av bay. The vents should be an odd number (1, 3 or 5) which are evenly spaced, this helps prevent a direct path through the middle of the av bay.

This is my Competitor 3 Av bay. The one of the 3 vents is visible on the top of the red switch band. The altimeters are a Featherweight raven (main altimeter) and a Perfectflight Stratologger (as backup).
Image

This is my 54mm Darkstar Av bay. It has a single Featherweight Raven altimeter.
Image
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Re: Electronic recovery andDual Deployment

Postby PJR » Sat Jan 19, 2013 7:52 pm

Lamp Thanks for the thread on Dual Deployment.

Rockets for DD do they have to be made of fibre glass/composite materials because of the high speed of deployment of the main chute, or can the tube just be reinforced around the lip. I am asking because at our launch site at Doonside we have a weight restriction on our rockets and we can drift into the trees easily when we get a bit of height.

Phil

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Electronic recovery andDual Deployment

Postby Lamp » Sat Jan 19, 2013 9:09 pm

G'day Phil, electric dual deployment, being initiated by either barometric and/or accelerometer sensors is more accurate for deployment at apogee than motor deployment and is therefore generally less likely to cause a zipper. If you are worried about getting a zipper from the main chute deployment, you can always use a larger drogue. Rather than using a drogue to slow the decent to 60 to 65 fps (what I prefer for glass rockets) you can choose a drogue to slow the rocket to around 45 to 50 fps, or whatever you are comfortable with.

I have a preference for glass rockets because they are so tough. The LOC Sparrowhawk I'm currently building is a cardboard rocket and is being constructed for dual deployment. I could leave it as it is and it would be fine but I'm going to give it a layer or two of 4oz glass because I'm less likely to damage it during transport and storage. I'm hard on my rockets. ;-)
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Re: Electronic recovery andDual Deployment

Postby Lamp » Sat Jan 19, 2013 9:59 pm

Avionics bays are normally made from coupler tubes but they can come included with some kits and can be purchased as a separate add on kit.

Performance Rocketry kits are "Bare bones" so you can make things how you want them. This is the coupler tube and the bulkheads for the Av bay from my "Little Dog" kit. You have to supply and build the altimeter sled as you want it and supply the eye bolts or u bolts and all thread rod(s). If you want a "switch band" you either have to cut it from the body tube or purchase one.
Image

Here is a LOC Av bay kit, everything except the altimeter, switch and wiring is included. Inside the coupler tube is a "Stiffy tube" which is glued in to support and locate the bulkheads.
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This is a "Blue tube" av bay kit, everything is provided except the altimeter, switch and wiring. As Blue tube is much stronger material than cardboard, the blue tube kit provides support rings to glue in rather than a full "Stiffy tube" like the LOC kit.
Image

This is the "half coupler" Av bay I made for my smoke. After it zippered I decided to make it DD but I wanted to keep the length the same as the original. This Av bay uses the top half of the coupler allowing me to fit a K550 size motor in the rocket. The dual sleds let me put a Raven with power perch as main altimeter on one and Stratologger and 9V battery as backup on the other.
Image
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Re: Electronic recovery andDual Deployment

Postby Lamp » Sat Jan 19, 2013 10:34 pm

There are many ways to make up a pyrotechnic charge, from putting the black powder and e-match head on tape and taping it up to putting the black powder and e-match head in the tip of a rubber glove finger and taping it up. What I do for charges less than 2 grams though is use a micro-centrifuge tube. The tubes come in two sizes - 1.5g or 2g

This is how I do it, and the things you need are: micro-centrifuge tube, e-match, flexible electrical tape, black powder, "dog barf" (not in the photo) and masking tape
Image

The first step is to cut off the very end of the tube and thread the e-match through the hole. If the hole is not big enough,use a hobby knife to enlarge it.
Image

Next use the electrical tape to seal the end of the tube so the black powder cannot get out
Image

The tubes are marked in ml, and about 1 ml = 1g of black powder...so pour in the amount of black powder you need.
Image

Next fill any space with "dog barf" and close the cap, this ensures the black powder will stay in contact with the e-match no matter what happens.
Image

Finally I use masking tape to seal the lid and use a pen to label the charge.
Image

For charge holders, there are commercial ones you can buy but I have used short lengths of 1/2" aluminium tube epoxied to the av bay bulkheads (You need to really rough up the end of the tube so the epoxy sticks and make a really good fillet), used "Estes motors" cut to length and epoxied to the bulkhead or, if I am using kevlar shock chord, I have taped the charge to the quicklink and the end of the shock chord. Do not cut the e-match wires too short or coil them because you want to allow for some movement during launch.
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Re: Electronic recovery andDual Deployment

Postby Lamp » Mon Jan 21, 2013 4:40 pm

The reason it is good to use a logging altimeter is so you can record and look at the data from the flight after the event. This can tell you things about the flight you cannot find out just by looking at your rocket.

All manufacturers have their own software for downloading the data and they are not the same, the following is a selection of flight data from a few different altimeters so you can see the kind of data you can get. You can get information about pyro firing, Altitude, Rocket velocity in some cases, Battery voltage, Acceleration and other measurements


A plot from a G-wiz HCX
Image

A plot from a Perfectflight Stratologger
Image

And a plot from a Featherweight Raven
Image

From this data you can determine how things have gone like deployment events, how long it took your chute to open and what your decent velocity was like under drogue and under main.

If you zoom in on the acceleration, you can get an idea of the burn characteristics of the motor. This is not the same as a static firing because a rocket actually moves, but it is good for an idea and the time data is good. Here is a zoom in of the data from my 54mm Darkstar on a J570W, the burn is very regressive and lasted for about 1.85 seconds. This is pretty well exactly what the motor characteristic curve from Aerotech says it should be.
Image

I hope this thread helps you if you are wondering about altimeters and Dual deployment. This is by no means comprehensive information but is just what I have thrown together hoping it will help some people. I hope that if you have any ideas about how this thread could be improved or and other comments you would post them.

Cheers,
Pete
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Re: Electronic recovery andDual Deployment

Postby PJR » Mon Jan 21, 2013 5:29 pm

Lamp great information thanks for posting.

I know you said that altimeters are personal preference but do you have a favourite? In your AV bay your back up is different to your main is that because thats what you had, or would you like to use the same brand if you had a choice

Do you use wide strap/webbing for your shock cord. If so how do you attach you parachure to the cord

Phil

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Re: Electronic recovery andDual Deployment

Postby str8up » Mon Jan 21, 2013 6:25 pm

Thanks for the thread Lamp.
You made up the pyro charges then mention the charge holders. Do I assume that these are just tubes to hold the made up pyro charges in place at the end of the AV bay?

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Re: Electronic recovery andDual Deployment

Postby Lamp » Mon Jan 21, 2013 8:19 pm

Good questions! :mrgreen:

I must confess that my favorite altimeter is the Featherweight Raven, I find it very good, it is very powerful (even if I have not used it to its full potential) and it allows you to see every parameter you could think of in the downloaded data. I would be fine to use two of these in my Av bays but I like the idea of fully independent and different systems so it is extremely unlikely both will fail, added to which, the Stratologger is also a good dual deployment altimeter and is about 1/2 the cost. One thing I should also mention is that altimeters should be oriented along the axis of the rocket and some altimeters (especially older types) have an "Up" direction requirement, if they are mounted upside down they will not work. Both the Raven and Stratologger can be mounted either way up.

I use Kevlar shock chords where space is limited and I want something very strong for the weight and space and I use tubular Nylon shock chords where these things don't matter. I would use Kevlar all the time except for two reasons, firstly it is thinner and narrower which means you are more likely to get a zipper (I know you can get tubular and strap Kevlar and I do use that) and secondly it has no "give" or stretch which means you are more likely to get a zipper. It really just depends on the situation and what I think at the time. The downside of tubular nylon is that it needs to be protected from hot ejection gasses, typically by a nomex sleeve.

For the parachute attachment to the shock chord, I use a "Quick link" through a slip knot. It does not matter if I am using 1" tubular nylon or 1/8" tubular Kevlar. I do it this way because it lets me easily change the location of the chute/streamer along the shock chord if I need to. Here is the parachute attachment on my 54mm Darkstar.
Image

The charge holders are just that....they are there to hold my made up squibs (Pyro charges). Some commercial holders do not require the made up charges...you thread an e-match into them, pour in your measured black powder and tamp in a cardboard plug but I like to make up my charges (sometimes the night before a launch) and I find it easy and safe to do it this way. Some people who make charges the way I do use hot glue or epoxy to seal the hole before pouring in the black powder but I'm not that organized and the electrical tape is quick and easy! :wink: This is the top on my Competitor 3 av bay with the tape (used to hold the squib into the holder and the used squib removed, it is just half a used 18mm Estes motor.
Image
(Sorry for the quality of the photos...it was getting dark and they were taken quickly without extra lighting)
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Re: Electronic recovery andDual Deployment

Postby str8up » Tue Jan 22, 2013 11:49 am

Are the "squibs" just a push fit into the holders? Or does anything else hold them in there?

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Re: Electronic recovery andDual Deployment

Postby str8up » Tue Jan 22, 2013 11:59 am

Was just thinking about the effects of inertia on the aft squib - the one facing down - at launch and how it is kept in the holder.

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Electronic recovery andDual Deployment

Postby Lamp » Tue Jan 22, 2013 1:09 pm

I run masking tape over the top of the squib and down the sides of the holder to hold them in and a bit of tape around the holder to make sure that tape does not come off.
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Re: Electronic recovery andDual Deployment

Postby PJR » Thu Feb 14, 2013 9:10 pm

Lamp the Raven 3 altimeter that Blake sells come in 2 versions 250G or 70G. They both have the same write up? Which one is better, Why no just sell one both same price.

When you set up the drogue chute charge do you have to use a higher pressure as I would think that it is trying to push the drogue chute further down the B/T?

Phil

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Re: Electronic recovery andDual Deployment

Postby Lamp » Fri Feb 15, 2013 6:10 am

The two versions of the Raven use different accelerometers. The 70g version is more accurate but there is the potential for it to be damaged under excessive g forces, the 250g version is slightly less accurate but more robust. If you are flying "normal" type rockets the on "normal" motors the 70g version is great, but if you are thinking if flying a min diameter rocket on a high thrust motor you really should think about the 250g version.

You should ground test your pyro charges in your rocket if you are unsure if they will work....theoretically you are right but it is more dependent on the size of the compartment than the friction due to the length of the length of body tube. If you are worried add and extra 0.1g of BP or if you run 2 altimeters and have redundant charges set to go off a couple of seconds later than the primary pyro you can make that a little bigger. For example, I use a 1.3g primary and a 1.5g backup (set to go off 2 seconds later) in my competitor 3 drogue compartment and a 1.0g primary and a 1.3g backup for my main (primary at 700' and backup at 500').

I hope this helps... :D
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