Dual Depolment basics

I'm planning to build my first duel deployment rocket. My knowledge of design is based only on what I've read.
A couple of basic questions.

1. Is there a good reason why the initial rogue deployment is not triggered by the ejection charge within the motor (in my case a Cesaroni 29mm or 38mm)? The second stage main parachute being altitude triggered by an electronic charge.
I can only think it is the accuracy of the timing of the initial charge that gives an advantage to an apogee driven charge rather than the motor charge.

2. If I choose to use two electronic charges and drop the motor charge, is it usual to scrape out the Cesaroni motor ejection charge and fill the void with epoxy? I've read this but would appreciate confirmation that this is a tried and tested method.

SO.

I use the altimeter for the deployment of the drogue at apogee and leave the motor charge in for a backup just in case there is a problem with the altimeter.
I have seen this save more than 1 rocket, when the altimeter has not fired the charge.

The main is than deployed by the altimeter.

Space Oddity said:

I'm planning to build my first duel deployment rocket. My knowledge of design is based only on what I've read.
A couple of basic questions.

1. Is there a good reason why the initial rogue deployment is not triggered by the ejection charge within the motor (in my case a Cesaroni 29mm or 38mm)? The second stage main parachute being altitude triggered by an electronic charge.
I can only think it is the accuracy of the timing of the initial charge that gives an advantage to an apogee driven charge rather than the motor charge.

2. If I choose to use two electronic charges and drop the motor charge, is it usual to scrape out the Cesaroni motor ejection charge and fill the void with epoxy? I've read this but would appreciate confirmation that this is a tried and tested method.

SO.

Click to expand...

1) motor deploy at apogee is what everyone NOT using DD ascribes to, but even with drilling, the results most times aren't perfect. Modeling in Rocsim or OP may give you a fighting chance, but off angle trajectories and a million other factors work against you. You are right in the assumption the baro sensor will trigger at apogee more likely than the motor charge. I leave (if it works with the math) the motor charge in as a backup.
2) Most of the time, just cutting the paper cap on a CEZ and dumping out the powder is sufficient. If you have shear pins or really are worried about venting thru the expended motor case-most time the transient pressure wave from the main will blow the tube first before it vents. If it makes you feel more secure-remove the delay, dump the charge and then add 5 min epoxy BEFORE you re-assemble everything. You don't want to glue your reload in the case! I just throw some dogbarf in and tape over it for high alt birds that exceed the delay time of the motor-max you can get is about 14 secs anyway. Works the same with AT but DON'T use epoxy in the delay well-you will hate life after recovery.

When using DD with motors that come with an ejection charge, I take out the supplied powder and fill the hole. 5 min epoxy would work... so does hot glue. So does Fun Tac. As Fyrwrxz said, the baro sensor is a LOT more accurate than the drilled delay in the motor. I know: it's frightening to trust something you've never done, and take the delay out. I get that. But I think you'll find that, once you become comfortable with the process, you will trust them a LOT more than you will a drilled delay.


Later!

--Coop

I leave the motor eject in as a backup. I just make sure it is set for a couple of seconds after the simulated time to apogee.
The goal is to let the electronics set off the drogue, but a little backup can go a long way!!!!

Unless I have a rocket thats coast phase is longer than the delay I leave the motor ejection and use it as redundancy for the drogue. This may have have saved my L2 flight. If its not a long coasting rocket I drill the delay to +2 seconds after apogee as a backup since most motor delays have about that kind of accuracy I shouldn't be early.

Having electronic deployment at apogee prevents issues with motor eject if the flight deviates from straight up. For instance, if it weathercocks bad, apogee is still apogee, and the motor eject would be very late. So, as others have said, motor eject is good for backup, just be sure there's enough bp, you can always add a gram or two as needed.
For my first DD flight, I had two altimeters and left the motor eject as a third charge. Could've scraped it out and squirted some lube on it, but chose to have the extra redundancy.

Coop said:

I know: it's frightening to trust something you've never done, and take the delay out. I get that. But I think you'll find that, once you become comfortable with the process, you will trust them a LOT more than you will a drilled delay. --Coop

Click to expand...

So, true, as this is where I am.....while attempting my L1 cert. During my attempts, I used AT's H123W (now shipping as the EZ type - a 14 second delay ). In both attempts to drill the delay down to 8+ seconds using the AT Universal Delay tool (my prefect and another L3 overseeing the process), the actual delay seemed to be about 4+ seconds after burnout. As one might guess, this inaccurate deployment causes havoc during the flight, and was determined by my prefect to be the primary cause of failure :sad: during my 2 attempts. From talking to many of the certified fliers on the launch line, all of them encouraged me to move to altimeter-based deployment, with more than one saying "I wouldn't fly without it!".

I'm now working through testing a new DD setup on my Excel, and it's definitely nerve-wracking the first few times...but being able to hit your deployment right at apogee is a B-E-A-yew-tiful :eyepop: sight! As mentioned above, I'll still use the motor's ejection charge as a backup (the thought of reaching past a 14-second coast phase seems incredible!) ...

Best wishes for many successful and exciting flights!

Just to get a bit familiar with DD. I built my first DD to use the motor eject for the drogue. My drogue chute was large enough to bring in the rocket slow enough to prevent damage(if I didn't have the electronics set correctly) then my altimeter fired the big main at 300'. I was only going 850' so using the larger drogue wasn't a problem. I can easily modify now to use the DD with the dual event capability of my barometric pressure activated timer using larger motors to 2k' and higher. (With a small drogue,) Having little experience with electronics , this was an easy try-out. And very informative. Large DD rockets look great coming in with all the parts connected and moving slow in the air.
have fun

Thanks to all for your very informative replies. I hadn't considered the motor charge as backup but will.

I have one final question to ask regarding the electronics.
Here in the UK they are few and far between and expensive. I've narrowed it down to two, the Aim USB at £80 and the Stratologger (the predecessor to the CF - I can't find an available CF yet) at around £60. Having read both manuals there doesn't seem a lot to choose between them but I'm slightly in favour of the Stratologger. Having said that, downloading data from the Aim seems easier as the USB port is included.
I'm completely bemused by the "beep" system, seems a bit archaic. Then again I suppose you get what you pay for.

I'd appreciate any views from those that have used either of them.

SO.

I've flown the CF (which has the same functions as the stratologger, just a smaller board) and it's very nice, you just need the datacap cable to download data from the flight. The beep system is pretty simple to understand once you hear it a few times, but downloading the flight data gets you a lot more information with either altimeter. I haven't flown the Aim USB but it's a more complex unit with airstarts and recording more like the RRC3. I'd say both are good options, but if you want more advanced options I'd probably go with the USB.

Edit: You could also always go with both, use the Aim USB as the main altimeter and the Stratologger for redundancy. I've heard the Stratologger is an excellent backup altimeter as it can be set to deploy at apogee +1 second to prevent both charges firing at once. I'll be trying something similar in a few weeks with a RRC3 main and SLCF backup.

Also- even with redundant altimeters, having the motor backup (drilled to predicted apogee plus a second or two) can't hurt just as a backup.

You need some sort of beep. Once the altimeter is buttoned up inside the rocket, you won't be able to see it or what it's telling you if it uses anything else. Beeps also help you find your junk once you land out in the thick.

grouch said:

You need some sort of beep. Once the altimeter is buttoned up inside the rocket, you won't be able to see it or what it's telling you if it uses anything else. Beeps also help you find your junk once you land out in the thick.

Click to expand...

Definitely. My Magg landed in a corn field a few weeks ago, and it was practically impossible to find even flying a drone over the field. Eventually after around an hour and a half someone else found it accidentally, but having a beeper would have helped (only altimeter was an Altimeter3 which records only with no sound). I got a GPS pet tracker after that adventure which should help with tracking, but having a beeper would still really help if landing in crops.

During the static testing of my DD config (using the StratoLoggerCF), I was surprised as to how quiet the beeping actually is, once you've gotten everything buttoned up. My ears are 50 years old, so they might not hear as well as some, but nonetheless it would be difficult for me to locate my rocket by sound alone if it was more than 10 feet away.

What got me thinking about this issue was a feature of the StratoLoggerCF....after a flight, it will play a 'warbling siren' sound every time it replays the beep codes for altitude achieved - I chuckled out loud when I heard it start 'warbling' after the static test - very quietly . Not much sound comes out of the av-bay port holes!

Hope all your flights land safe & sound in the wide open spaces :clap:

SO you'll need to buy States side as no UK stock and will take forever. Can join me on my order of wanted.

I love, love, love altimeter apogee deployment. Guess and check delays stink, big time.

That said, if I am a little unsure of new electronics or other aspects of a configuration, I will leave an un drilled motor charge in place. I figure a zipper beats a core sample.