Staging electronics setup

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mccrocketman

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Hi All-as my previous posts can attest, I am new to staging. I got my hands on a Wildman 2-stage rocket, and I was wondering if I could get advice on the best way to set up the staging electronics? My plan is to use a small BP charge to separate the booster from the sustainer, and and to ignite the sustainer via electronics in the sustainer body tube. A conduit will be placed through the RR CRs, and I was thinking of putting a small e-bay w/ timers right above the motor. Suggestions on how to do this? I don't like the idea of "break-away" wires that run up to the main electronics bay.....too much of a risk of getting caught/not breaking away at apogee. Any pictures/help would be much appreciated!
 
I'm working through my WM Jr. two stage build right now, which is mostly complete.

I use a Raven in the sustainer ebay to control sustainer ignition under criteria of time, altitude, and velocity. A JST connector links the wire running through the conduit to the ebay, and it pulls apart when the apogee ejection charge goes off. Hasn't flown yet but ground tested very well, prevents any issue with having to break wires and if you strain relieve it correctly (tape it to harness above connector and tape lower wires to inside of body tube) it should yield a reusable, reliable connection.

I'm not sure what specific electronics you're referring to with timers but for literal timers (burn at x seconds after launch) I think most people have moved toward altimeter-based systems like the Raven or MARSA in order to prevent erroneous upper stage ignition. Whatever you use, make sure you look at the current requirements of the igniter, the limits of the electronics, and what the battery is able to source. Many people prefer CTI motors in the sustainer due to their use of an ematch with the pyrodex/etc pellet inside the motor making it easier to ignite.
 
smapdiage9 said:
I'm working through my WM Jr. two stage build right now, which is mostly complete.

I use a Raven in the sustainer ebay to control sustainer ignition under criteria of time, altitude, and velocity. A JST connector links the wire running through the conduit to the ebay, and it pulls apart when the apogee ejection charge goes off. Hasn't flown yet but ground tested very well, prevents any issue with having to break wires and if you strain relieve it correctly (tape it to harness above connector and tape lower wires to inside of body tube) it should yield a reusable, reliable connection.

I'm not sure what specific electronics you're referring to with timers but for literal timers (burn at x seconds after launch) I think most people have moved toward altimeter-based systems like the Raven or MARSA in order to prevent erroneous upper stage ignition. Whatever you use, make sure you look at the current requirements of the igniter, the limits of the electronics, and what the battery is able to source. Many people prefer CTI motors in the sustainer due to their use of an ematch with the pyrodex/etc pellet inside the motor making it easier to ignite.
Click to expand...

I was planning on using a Perfectflite MicroTimer4 and maybe a Raven as a backup (Raven is a little more complex-looking for simplicity). Is there any way you could post images of how you set that up?
 
It looks like this:

mkJgP3pl.jpg


Bulkhead terminal is wired to raven in the avionics bay. I bought some extra JST connectors and used that as my intentional "break point" so when the apogee charge goes off it will disconnect the wires as the laundry unfolds.

The Raven is probably technically more complex but if you've already got one it's really easy to set up to ignite the motor at x seconds after burnout within those constraints I mentioned above, which is probably the safest way to do it.
 
This may help a bit, build thread on 2-stage Wildman Vindicator Jr. Basically same as yours just split-fin.

https://www.rocketryforum.com/showt...ldman-Jr-kit-to-a-2-stage-build-Vindicator-JR

Some highlights.

Conduit for staging wire only needs be long enough to pass through CR's + a bit.
My first couple of 2-stages, I ran long conduit all way up fin can to just below coupler. This ended up biting me later. Recovery cord pulled it away from wall and I could never get inside the bend back flush.

Now I run conduit just far enough that won't happen. Conduit is 3/16's "Foreign" brake line, available at any car parts store. 4-6 bucks for 2-4ft.

Bottom of conduit run to edge of retainer to aid in fishing wire.

DSCN2102.jpg DSCN2103.jpg DSCN2104.jpg


Terminal block on av-bay .

DSCN2176.jpg

Av-bay utilizes 2 tie rods with sled free floating [no tubes glued on] sled is cut so it fits tight front to back & side to side, so it cannot move when BP's installed. Sled is also cut so it sit's low in bay, allowing for more room on top of sled to install gear. If it was centered then no room for 9v to clear. # 8 threaded rod for tie rods.

DSCN2177.jpg

Finally I now use female JST connector to slide match wire into. Wires are pulled through, small tabs bent to increase "pull" friction a bit, then trimmed close. [ tabs are exaggerated for pics, in reality cut close , so they cannot short by touching each other.]
There is some debris on table under pic on right of connector, looking like wire, ignore.

This technique works great. If you tape match wire to nozzle cap on motor, [needed if using separation charge] when motor starts, it will pull match wire free, completely ejecting it from airframe with cap. This leaves nothing to interfere with apogee deploy or tangle.

These pics NOT in build thread, this is something I just recently came up with & use. Quite successfully, I might add.

DSCN5263.jpg DSCN5266.jpg

I use motor eject for simplicity in this size booster, with a timer in interstage coupler for separation charge, at motor burnout.
Sustainer motor ignition handled from Sustainer av-bay. I stage based on reaching altitude X and coast time or NO fire.
 
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I've had dozens and dozens of multi stage flights (2, 3, and 4 stages) with a Raven in the avbay doing stage separation, ignition, and dual deployment. I use mini dean connectors (very similar to JSTs) to separate the tail end leads from the avbay.

I strongly recommend against using a timer for stage ignition. Use something smart enough to NOT ignite the sustainer in the event of a flight abnormality.

...Fred
 
Repeat....MARSA-NET and HEI.
Forget all the wiring, connectors and conduit.....and do it right.....

Did you all even LOOK at the webpage?
 
FredT said:
I've had dozens and dozens of multi stage flights (2, 3, and 4 stages) with a Raven in the avbay doing stage separation, ignition, and dual deployment. I use mini dean connectors (very similar to JSTs) to separate the tail end leads from the avbay.

I strongly recommend against using a timer for stage ignition. Use something smart enough to NOT ignite the sustainer in the event of a flight abnormality.

...Fred
Click to expand...

Fred,

I've had some good conversations with you about your techniques, and they're impressive. You have tracking electronics in everything, your designs are well thought out, and your execution is awesome! Most of all, your attention to safety is appreciated. Whether it's shunting the upper stage igniter wires or programming your Ravens to be as safe as possible, you've thought of it!
 
FredA said:
Repeat....MARSA-NET and HEI.
Forget all the wiring, connectors and conduit.....and do it right.....

Did you all even LOOK at the webpage?
Click to expand...

I already have multiple Ravens and have done boosted dart separations w/ them. MARSA-NET looks far too complex for me haha! RF is not as reliable as hard-wiring in my experience.

Thanks guys-the pictures have helped me a lot. Anything simple and effective is best.
 
I am just starting to build a Shape Shifter 2 Stage Jr. and am really considering my electronics & build options before I get very far. My first 2 stage so I am new to this.
I have a MARSA54L great flight computer. I was thinking of getting another one with the bridge systen and two Mrf pyro sensors, one for the booster for separation and one for sustainer ignition thus elliminating the conduit. However I still need an altimeter in the booster for chute deploy at around 500ft. as the MARSA Bridge can only talk to the Mrf sensors up to 60 ft. apart. Can the sustainer ignition also be the booster separator or would that possibly fry the booster electronics and use to much energy for the sustainer flight?
 
Pretty hard not to have an altimeter in each section of the rocket.
Once you have that, add the MARSA-NET to eliminate wiring and put the charges where you want them.

I my mind, that's a MARSA-54L for each EBAY.
Plus a remote charge in the booster interstage coupler to push the sustainer off - that remote talks to the booster EBay.
A second remote on top of the sustainer motor for HEI - that remote talks to the sustainer EBay.

No wires need to cross any parachute bays.
No need for connectors that must un-connect at the right time...
Simple and clean

Nice stuff John!
 
Not sure what you mean by HEI but I'm assuming it means high energy ignition. By putting the pyro remote on top of the sustainer motor how is ignition being accomplished?
 
I think he means head end ignition, where a hole is drilled through the delay grain at the top of the motor and your igniter/ematch is inserted from above. This method requires you to pot the igniter in place with epoxy (I think?) in order to ensure the combustion chamber doesn't leak through the top.
 
Yes, HEI = Head End Ignition.
The only way to fly -- no crazy conduit or such to get wires aft and more importantly, no wires in the throat/core that have to clear.....
 
Very cool, I like that idea alot. I take it the hole through the delay is just large enough for the igniter to fit through and any particular epoxy to use for this?
 
Just a reminder. HEI is not a manufacturer supplied motor option, so adding HEI is a motor modifications only allowed under TRA Research Rules. It is not allowed under the standard NAR or TRA High Power Safety Code (NFPA 1127).

Bob
 
bobkrech said:
Just a reminder. HEI is not a manufacturer supplied motor option, so adding HEI is a motor modifications only allowed under TRA Research Rules. It is not allowed under the standard NAR or TRA High Power Safety Code (NFPA 1127).

Bob
Click to expand...

Thanks for that clarification, Bob! While this is a very cool concept, and I love the elegant design, I have to say that having an initiator in a motor scares me a lot more than having an initiator in an ejection charge. Folks, let's be really careful out there!!!
 
WillMarchant said:
May be time for a separate thread dedicated to "HEI best practices"? I'd be very interested in that...
Click to expand...

That would be a very good idea Will. Hope the folks in the know consider it. I'm not convinced that a shunt is a valid safety device unless one actually tests it out on the bench to see if prevents whatever ignition event one is trying to
inhibit doesn't fire. My problem is it seems with testing that firing an altimeter into a dead short, could dork the thing and if one doesn't test, maybe the altimeter could overcome the short and send enough current to activate whatever
ignition device they are using for staging anyways. Especially if it is a low current ematch augmented ignition igniter. Kurt Savegnago
 
ksaves2 said:
I'm not convinced that a shunt is a valid safety device unless one actually tests it out on the bench to see if prevents whatever ignition event one is trying to
inhibit doesn't fire.
Click to expand...

Fred A said "shunt AND disconnect". His one-switch method for doing both is elegant and robust.
 
jderimig said:
Fred A said "shunt AND disconnect". His one-switch method for doing both is elegant and robust.
Click to expand...

Hi John,

Ok, so does that mean disconnect the shunt so it's no longer in place so one is ready to fly and/or is the disconnect to take the igniter out of the circuit? People say they put a parallel conductor or shunt across the terminals of the igniter and
say, "There, it's safe." The idea is the dead short takes the current so the "igniter" doesn't fire. Unless one tests it, how do they know it "won't" fire? If one is disconnecting the igniter from the circuit (via a switch say) while setting up, why in the heck do they need a "shunt" too? Let's say the altimeter's FET can blast current through the shunt and enough passes in parallel to light off an ematch augmented igniter? Big trouble then. Now if someone is using a high current igniter situation a shunt might
prevent an accidental ignition event.

Look, I know folks have been flying multi-stages successfully for ages but I have a very tough time wrapping my head around this idea of a parallel shunt as a "safety device" without a test to prove it's going to prevent an unintended event for a
"given" setup. A serial lockout switch that breaks contact through one leg of the ignition circuit is obvious. I can fathom that. Not trying to be a difficult child but trying to avoid a false sense of safety in these situations

Just like in the old days when NAR/TRA required a safety interlock switch on every ematch on an L3 project. Don't believe me? Look at the cover of Extreme Rocketry, issue 52, March 06 and you will plainly see 6 interlock plugs on the ebay.
Two for on/off of the two altimeters and four more for each on the ematch channels for deployment. Stupid requirement then and if any TAP/L3CC is making people do that, the person needs to get another official to use.
Kurt Savegnago
 
Kurt,

You are correct in your suspicion. Shunts by themselves are not guaranteed to be safe. Current will flow through both the match and the shunt. In the case of energy sources with very high current capacity (some lipos), enough current can flow through the match to set it off. For sources with relatively high source resistance (NiMH 9v for example), then the shunt may pull the batt volt low enough to prevent appreciable current through the match.

The shunt does protect from limited sources of energy like static discharges.

[video=youtube;sasoJB_P0Rg]https://www.youtube.com/watch?v=sasoJB_P0Rg[/video]

Disconnecting the bat
 
Last edited:
glenbo said:
Yes good to know, safety first always.
Click to expand...

Safety is good. Having done dozens of multi-stage flights, I can offer the following advice...

First, start thinking about safety when you first start the rocket design. It is a lot easier to design in safety at the start than to try to make a design safe after it is built.

Second, it is real important to figure out how to have the sustainer motor not light until you want it to. Three tips here:

1. Use an altimeter that incorporates an altitude check and not just a timer. There are somewhere around a half-dozen altimeters that can do this. They can help keep the sustainer motor from firing on the pad. And, they can prevent the sustainer motor from firing if the flight is not nominal. Programming the altitude check is not quite as easy as some people think, though, and it is easy to get it wrong. I could provide several examples from my own experience, but my recommendations are to make sure that you understand exactly how your electronics work and to have your setup and underlying simulation reviewed by someone who has done it before.

2. Use switches to shunt and/or short your igniter leads. I always use a shunt (to short the output leads), and in many cases I also use a short (disconnecting one of the leads on the igniter-side of the shunt). It is important to recognize that a shunt still allows current to pass through the igniter if the electronics fire. The purpose of the shunt is to reduce that current to below the level that fires the igniter. The current that will pass through the igniter is a function of many things, including the relative wire lengths and gauges, the igniter characteristics, the altimeter design and the type of battery that is used. Be very careful about using a LiPo to fire the sustainer if you are using a shunt, and if you don't understand why these variables are important, then ask questions.

3. Do an all-up test of the electronics (ideally) just before setting the rocket on the pad. All of my designs are configured so that I can do an all-up test. In the all-up test, everything is assembled and everything is turned on just as it will be when you arm the rocket, except that the igniter is not inside the motor. This is pretty much your last line of defense against a malfunction. If the all-up test passes, you turn things off, insert the igniter and put the rocket on the pad. There are many design features you might implement in staging that could make the all-up test harder to perform, including many things discussed in this thread. However, if you consider those features in the initial design, you might be able to build in a way to conduct the all-up test when the time comes. My personal rule, though, is that if some aspect of a design would prevent an all-up test, I won't do it.

Finally, I would recommend keeping others away from the pad when it comes time to arm the sustainer. No one has ever actually witnessed me arming a sustainer from closer than a hundred feet or so, and for flights with larger motors, it is further than that.

Jim
 
jderimig said:
Kurt,

You are correct in your suspicion. Shunts by themselves are guaranteed to be safe. Current will flow through both the match and the shunt. In the case of energy sources with very high current capacity (some lipos), enough current can flow through the match to set it off. For sources with relatively high source resistance (NiMH 9v for example), then the shunt may pull the batt volt low enough to prevent appreciable current through the match.

The shunt does protect from limited sources of energy like static discharges.


Disconnecting the bat
Click to expand...

God Bless You John and thanks. I was expecting to be sucker punched and derided yet again on this. I am aware of static charges are an issue with ematches and suspected that was why some of them come with twisted wire tails.
Have heard stories about ematches "going off" with static electricity and figured it's easy enough to take precautions for storage. Don't know if some of the stories are apocryphal but I suspect some are true.
Of course there are some of the older devices that if one attaches the battery polarity in reverse any matches attached will blow. That's easy to prevent if one just simply takes extra care in connecting batteries up to deployment devices.

So getting back to shunting a two stager. Those that do it are they trying to "prevent" static discharge from setting off a low current augmented igniter? That would seem superfluous to me as the arrangements seem to be totally enclosed and
actually "very enclosed" in the case of HEI. Why go through that trouble then?

If seems to me that a simple lockout switch on one leg of the igniter circuit would be all that's necessary for safe prepping of the rocket. One would need to be certain battery polarities would be correct of course. If there was a separate pyro battery that could be switched too, I'd mock up everything at home with bare matches and the igniter connected sans propellant of course. Turn on the igniter, turn on the pyro battery and then turn on the electronics.

What? I hear a gasp? O.K. now I would do a test with the pyro battery off, and the igniter disconnected from the circuit but sometimes if one turns on a deployment device
and it detects a fault, you can't just turn the switches on and the device now "feels good" and starts beeping O.K. that continuity is established. Some devices will only give the "ready to go" indication if all the ducks are in a row at startup. You can't fix the continuity while it's in default and expect it to start giving the A O.K. sign. Nonetheless, I'd rehearse the protocol at home with the rocket, sans propellant including Rf tracker(s) running to be as certain
as I could that Rf wouldn't pop the staging circuit and I have the technique down for the checklist.

Ideally, a staging circuit would allow one to turn the device on and check the recovery circuits, send an indication that they are O.K. and show a default on the ignition circuit. One could then turn on the outboard pyro battery (if used) and then establish continuity of the ignition circuit last. The device would then give the OK sign if all was ready. I think that would be ideal and ditch the shunting thing.

Kurt Savegnago
 

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