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Staging Timer Questions / Suggestions?

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pcotcher

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I am working on a multi-stage Nike Ajax (Build thread in the mid-power section. It originally started as a TLP upgrade, but since has turned into a complete scratch project.

I am to the point in the project where I have to start integrating the electronics. I am planning on using a staging timer in a nose electronics bay, using a headphone jack as the release, as noted in this thread

I have the wired headphone jacks - so I'm all set on that front, however, I'm starting to question my original idea on the timer.

Based again on the article that I linked above, I had planned to use the Perfectflight Mini Timer 3G - the size is perfect for my electronics bay. Which, BTW, is a ST-11 - so I have a 1.1" diameter space in which I can fit this. It's over 10" long, so I have plenty of space lengthwise, but need to constrain this to the 1.1" diameter.

I was on the verge or purchasing the MT3G, but in reading the manual, I wasn't crazy about the programming method - as it sounds like it programs based on how long you hold down the switch. Since I'm looking to time this pretty close to the burn length of the motors that I'll be using in the booster, I need to be able to precisely program the timer.

While I can stop watch the programming time, I'm not sure my reactions are good enough to be able to let up at a precise 1/10th of a second moment. For example, if the burn time of the booster motor is 2.8 seconds, I want the timer to fire at 2.9 seconds - and I'm afraid that holding down the button is gonig to get me 2.7 seconds 3.3 seconds, etc. No way to fine tune the program.

So I guess I'm looking for suggestions and comments as to how to use the MT3G, or if there's a better one out there on the market that still fits in my 1.1" e-bay.

Thanks for your suggestions!

Paul
 

Luv2launch

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I have used the mt3d timer in my aerobee hi the programming method is tedious but it is possible to get the times you want it set for although it might take a couple trys to get it.
This stager might be a better option as it can sense motor burn out.
http://www.adeptrocketry.com/ST231.htm
I think I might pick up on of these for a future project.
 
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pcotcher

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Looks good - great features, etc. Only problem is the size - at 1.4" wide, it won't fit in my 1.1" electronics bay.

Same thing with the PML timers - good features, bad dimensions.

I guess that's the one thing that the MT3G has going for it - size!

Thanks,

Paul
 

hardinlw

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The Parrot or Raven altimeter http://www.featherweightaltimeters.com/ would support staging as well as parachute deployment. Altimeter deployment of the sustainer is needed in case the sustainer engine does not ignite. It is also useful when the sustainer ignites late and the rocket has arced over making the standard delay a bit long. :D
 

pcotcher

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Those are very promising - right size, I like the BOS feature, only drawback at all, is that the delays are pretty long, starting at one second - would rather be able to set a shorter delay before burn out.

Only other thing I notice on those, is that they're designed to ride mid-ship, instead of in the nose, so I have to run the ignition wires back over the board to the e-match at the bottom of the sustainer.

Want to have this timer board as far forward as possible to help with stability.

Keep the suggestions coming. I just looked up a bunch of brands last night, so I have a bit more to look through when I get a break today!

Thanks!

Paul
 

bobkrech

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Those are very promising - right size, I like the BOS feature, only drawback at all, is that the delays are pretty long, starting at one second - would rather be able to set a shorter delay before burn out.
The Perfectflite Micro timer is a good choice.

http://68.178.208.82/cgi/PF_Store/p...page&thispage=microT2.html&ORDER_ID=164863875

I don't not recommend you start the second stage while the first stage is still boosting. You will cook the booster and probably send it on a non-vertical powered trajectory. It's best to design the booster to drag separate and wait a second or so before you light the second stage.


Only other thing I notice on those, is that they're designed to ride mid-ship, instead of in the nose, so I have to run the ignition wires back over the board to the e-match at the bottom of the sustainer.

Want to have this timer board as far forward as possible to help with stability.

Thanks!

Paul
Remember current, not voltage, activates an igniter. This timer weighs only 6.5 grams and a relatively small LiPo battery can easily activate a properly made igniter. You should be able to make a complete ignition system that weights less than 25 grams, and it could be located on the top of the booster instead of the second stage without effecting the stability of a rocket that needs to utilize the circuit.

Bob
 

pcotcher

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And that's my bad for using the wrong preposition - I should have said AFTER burnout.

I have no intention of lighting before burnout - and want to drag separate, but then have the delay be only .5 seconds after burnout, so that the sustainer doesn't get any chance to start arcing over.

I actually have more on that topic in my build thread, referenced in the lead post (it's in the mid-power section).

As for the Pefectflite - that was my original choice, small, simple, lightweight, etc. The only problem that I have with it is the fidelity of being able to set the ignition delay - according to the manual, you just depress the program button the desired delay length, and hope that you can match the desired time.

I like circuits that have burn-out sensors, as I'd rather build my delay from that time. And then have a better programming interface - either dip switches or similar.

I've received some good suggestions in this thread, the Xavien looks like it's close, but doesn't have a short enough delay after burnout.

At any rate, keep the thoughts, suggestions and help coming - it's all valuable!

Thanks!

Paul
 

sylvie369

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I like circuits that have burn-out sensors, as I'd rather build my delay from that time. And then have a better programming interface - either dip switches or similar.

I've received some good suggestions in this thread, the Xavien looks like it's close, but doesn't have a short enough delay after burnout.
Being 1/2 second late in the delay after burnout may be better than what you get with 1/10th second resolution in a timer that starts timing at liftoff, in light of the variation in motor burntimes and also the inaccuracy in your guess about how much of the motor's burntime will be spent getting your rocket up to the acceleration needed to start the timer. If your timer starts at burnout detection, both of those sources of variation are gone.

I'm not sure if that'll make a difference to your project, but it's worth considering.
 

pcotcher

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Absolutely valid points, and yet another reason why I'm moving away from the Perfectflite MT3G, and would prefer to find something with a BOS...

At this point I'm leaning toward the FA Raven - as I like having deployment backups, not to mention just a pure DD ability, as I expect with the right loads this thing will be able to get up there pretty well. And we have nothing but small fields down here in the south (unless I hit one of the big regional events).

Thanks!

Paul
 

new2hpr

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I'll throw in my :2:

The PF minitimer is very straightforward to set. I usually get the time I want in a few tries.

However, I have to put in a plug for Adrian. The Raven is probably overkill for what you want, but a good kind of overkill! I believe (and Adrian can correct me) that you can set up conditions on the staging as well, so that it has to be at an altitude > z and/or velocity >v to enable the ignition. LOTS of possibilities for customizing the flight, or safeguarding so that you don't ignite the next stage while it's pointing down, etc. Also a cool challenge to make a complex flight (my favorite!).

-Ken
 

Adrian A

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However, I have to put in a plug for Adrian. The Raven is probably overkill for what you want, but a good kind of overkill! I believe (and Adrian can correct me) that you can set up conditions on the staging as well, so that it has to be at an altitude > z and/or velocity >v to enable the ignition. LOTS of possibilities for customizing the flight, or safeguarding so that you don't ignite the next stage while it's pointing down, etc. Also a cool challenge to make a complex flight (my favorite!).

-Ken
Thanks, Ken.

The Raven was designed to add some safety to staging and airstarts. You can set it up so that the ignition will only happen if the rocket gets up above a selected altitude before a selected time. That way, if it goes way off vertical (or worse, it's tumbling), the next motor won't start, but the apogee and main deployments will still happen when they should. I used this feature in my own 38mm 3-stage attempt at BALLS last year. The wire to my 2nd stage ignition broke during the 1st/2nd stage separation, and so the 3rd stage ignition was prevented. If I were using a timer (starting the motor 20 seconds into the flight, as expected) the results would have been ugly, maybe really ugly. But in this case, the sustainer came out without any damage other that getting scuffed up from landing with an unburned motor and a small chute.

As a new feature with the Raven's firmware, it also has an intelligent burnout detection and counter. It watches the rocket velocity, rather than the acceleration, to detect when a motor has fired and when it's done. That way, if you have a minor launch rod snag it won't think a burnout just happened, and if you're doing staging, it won't think that the separation charge is another motor firing. This was a request from a user who has seen rockets destroyed by premature separation due to acceleration transients while the previous stage is still burning. You can select any number of burnouts as a condition for firing the outputs. So if you wanted one output to fire after the 1st stage, and a different output to fire after the 2nd stage, you can set it up that way using the GUI.
 
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pcotcher

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Adrian -

Thanks for the further information - I was already leaning that way, so it looks like this will be the answer - I would assume that I can also simplify some of the scenarios that you described as well?

Look for an order soon!

Paul
 
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