First Electronic Staging - MPR Build

[Jmhepworth]

I cut off a part of the red cap to allow pressure to be relieved before the motor comes up to pressure. I also tape the ematch to a 1/16” dowel to hold the ematch at the top of the motor and then use the red cap to hold the dowel in place. All of my two stagers have been 38mm or larger. I don’t know that the dowel would fit in a 29mm, and I wouldn‘t be nearly as concerned that the thrust from the booster would cause the ematch to move away from the top of the motor.

 

[Buckeye]

Now I go with a separation charge. I just pack a little BP around the red cap of the Firewire and tape it up. Works great! I generally set the sep charge at 0.6 s after BO and then fire the sustainer at 1.2 s. That's been much better on the ISC!

Do you secure the Firewire/separation charge in some way or just let it dangle inside the interstage coupler?

 

[waltr]

I also use the ematch red cap a a roll of paper to make a charge for separation. 0.3gram BP is plenty.
I just leave it dandling inside the ISC.

 

[kjhambrick]

I also use the ematch red cap a a roll of paper to make a charge for separation. 0.3gram BP is plenty.
I just leave it dandling inside the ISC.

@waltr --

Do you bother to manage the separation charge ematch wires to keep the spent wires out of the sustainer exhaust ?

Thanks !

-- kjh

 

[Buckeye]

@waltr --

Do you bother to manage the separation charge ematch wires to keep the spent wires out of the sustainer exhaust ?

Thanks !

-- kjh

You can ask the same question about the sustainer motor igniter wires as well. My guess is that people don't worry about it.

 

[waltr]

Typically the separation charge wire is short and stays above the motor nozzle.
Ignition wires must be long enough the reach the Top of the motor. So will 'hang' down after motor ignition. Never been a problem.

 

[cerving]

Do you have to protect the sustainer motor with igniter in it from the separation charge? Is putting the plastic cap over the nozzle enough?

I’m looking to start simple as possible and separation charge seems like a “step 2”, but I also don’t have dual deploy experience yet (I have another rocket already built for beginning of next season to learn that) so might just be scared of BP charges!

A bigger issue is having the igniter on the sustainer slide away from the top of the grains due to the booster motor's acceleration. I don't think the plastic cap is quite enough. I use a stick to hold the igniter in place, and tape it securely to the sustainer motor's nozzle. Poke a small hole in the tape so igniter gases don't snuff out the flame, just like you would with any other igniter.

 

[Buckeye]

A bigger issue is having the igniter on the sustainer slide away from the top of the grains due to the booster motor's acceleration. I don't think the plastic cap is quite enough. I use a stick to hold the igniter in place, and tape it securely to the sustainer motor's nozzle. Poke a small hole in the tape so igniter gases don't snuff out the flame, just like you would with any other igniter.

Good call, especially with larger motors/cores. This probably is not an issue with the MPR motors I am using where the igniter is a pretty tight fit in the slot.

 

[bobbyg23]

Do you secure the Firewire/separation charge in some way or just let it dangle inside the interstage coupler?

Let it dangle

 

[wsume99]

A bigger issue is having the igniter on the sustainer slide away from the top of the grains due to the booster motor's acceleration. I don't think the plastic cap is quite enough. I use a stick to hold the igniter in place, and tape it securely to the sustainer motor's nozzle. Poke a small hole in the tape so igniter gases don't snuff out the flame, just like you would with any other igniter.

I'm imagining the stick extends past the aft end of the nozzle? Then run a few wraps of tape around the exposed end of the stick and then around the OD of the nozzle to hold the stick in place? Am I imagining this correctly? Just want to make sure I'm understanding how you do this correctly.

 

[Jmhepworth]

I do pretty much what Cris does, except that instead of tape to hold the stick in place, I use the red cap. Unless I misplace the red cap, and then I use tape the way Cris does.

 

[Rocketclar]

Do you secure the Firewire/separation charge in some way or just let it dangle inside the interstage coupler?

I don't secure so it kind of dangles. It's a fairly tight fit anyway. I hold the ignitor in the sustainer with Gorilla tape. And I stuff the ISC with dog barf and wadding.

 

[Rocketclar]

Do you bother to manage the separation charge ematch wires to keep the spent wires out of the sustainer exhaust ?

No. From the video, both the sep wires and the ignitor wires are seen just flopping around. Hasn't been a problem. The ends do get crispy. Here's a snapshot showing left over wires.

 

[Buckeye]

Slowly working on this build.

Sustainer electronics bay. I split the BMS 3.0" coupler that doesn't fit the BMS 3.0" body tube into an internal stiffy for the red Apogee coupler to give it a little more heft. I brushed on a few coats of polyurethane that I had laying around for some weatherproofing. I was afraid to use nylon all-thread on a previous HPR project, but I will use it here for mass savings.

 

[Buckeye]

Sustainer build is complete, including a conduit to run separation and ignition wires to the ISC. Next up will be electronics and av-bays.

 

[bobbyg23]

Slowly working on this build.

Sustainer electronics bay. I split the BMS 3.0" coupler that doesn't fit the BMS 3.0" body tube into an internal stiffy for the red Apogee coupler to give it a little more heft. I brushed on a few coats of polyurethane that I had laying around for some weatherproofing. I was afraid to use nylon all-thread on a previous HPR project, but I will use it here for mass savings.

View attachment 620719View attachment 620718

I would highly recommend against nylon for the avbay! You need strength here.

 

[Buckeye]

Nose cone bay for GPS tracker.

I tried some different things on this design, trying to minimize the alteration of the nose cone, yet making good use of the ample volume.

I made a sled attached to a bulkplate which slides into a hole cut out of the flat end of the nose cone shoulder. After reading another thread about well nuts, I decided to try them in this application. The bulkplate attaches to the nose with three (3) #6 well nuts (called "expansion nuts" at Ace Hardware.) I am pretty happy with the grip of the well nuts, and the installation was way easier than trying to glue t-nuts or hex nuts into the plastic nose cone.

The sled is long enough to accommodate both my Missileworks T3 and Featherweight trackers. I put a screw eye into the sled for attachment of a harness. I maintained the shock cord loop molded into the plastic nose cone as a harness attachment as well. I will use both to help distribute the shock cord loads.

 

[bad_idea]

Very neat. I use well nuts all the time through the sides of tubes, but it hadn't occurred to me to use them on the base of a nose cone like this. It's always inspiring to see how people generate new ideas!

 

[Buckeye]

Interstage Coupler

I also double walled this coupler for added rigidity. My initial plan was to fly the booster without deployment electronics, but I added provisions for an e-bay just in case by including a removeable aft bulkhead. I have an unbuilt Eggtimer Apogee which can fit nicely on the aft bulkhead, pancake style.

 

[cerving]

I've flown K-J's with just apogee deploy on the booster stage, it works fine. You WILL want dual-deploy on your sustainer, however... and a tracker.

 

[Buckeye]

I've flown K-J's with just apogee deploy on the booster stage, it works fine. You WILL want dual-deploy on your sustainer, however... and a tracker.

Yep, got all that. The only debate is motor deploy or electronic deploy in the booster.

 

[waltr]

My 2-stage also uses the BMS 3" school rocket kits.
Booster uses Motor eject and has worked fine for booster recovery.

 

[kjhambrick]

@Buckeye --

Stealing ideas from you for a future build ... ( )

Is the forward end of your ISC open so that the sustainer motor fits down into a 'cup' in the forward end of the ISC ?

Thanks !

-- kjh

 

[Buckeye]

My 2-stage also uses the BMS 3" school rocket kits.
Booster uses Motor eject and has worked fine for booster recovery.

True. My only concern is that I have some scenarios where the optimal delay for the booster is pretty small, like 3 seconds. This would require drilling down 11 seconds off of an H128-14A which is probably not a good idea. I would use electronic apogee deployment in this case.

I guess I don't need an optimal delay, since the booster will be tumbling/gliding at a low-ish speed. A deployment that is a few seconds late is probably just fine.

 

[Buckeye]

@Buckeye --

Stealing ideas from you for a future build ... ( )

Is the forward end of your ISC open so that the sustainer motor fits down into a 'cup' in the forward end of the ISC ?

Thanks !

-- kjh

Correct.

 

[jmasterj]

True. My only concern is that I have some scenarios where the optimal delay for the booster is pretty small, like 3seconds. This would require drilling down 11 seconds off of an H128-14A which is probably not a good idea. I would use electronic apogee deployment in this case.

I guess I don't need an optimal delay, since the booster will be tumbling/gliding at a low-ish speed. A deployment that is a few seconds late is probably just fine.

You should be able to safely drill down to 4 seconds, per previous comments from AT.

 

[plkap74]

I just did a pop test of a small interstage similar to this, 5 inch long, 2.6” diameter coupler closed on one end, motor sticking half way into it. It was my first time testing BP charges, so this might be old news to others, but one thing is that the online calculators gave such a small amount of BP that it may not have worked with my containment strategy (centrifuge vial, hole drilled in the bottom for ematch). Since the ematch sticks up a bit from the bottom of the tube, the recommended amount wouldn’t have covered the sparky bit. A buddy recommended I add enough to cover it, even though that was double or more what the calculator said. It worked fine at about 0.5g. Just a heads up in case you haven’t tried small charges.

I’ve also gone a bit wild with the vinyl cutter on it! Planning to test at the Jan 20 CMASS launch.

 

[Buckeye]

My 2-stage also uses the BMS 3" school rocket kits.
Booster uses Motor eject and has worked fine for booster recovery.

Do you shear pin the ISC to the booster?

 

[plkap74]

Do you shear pin the ISC to the booster?

Nope. Both sections have same fins/body tubes so drag separation seems unlikely and if it happens it happens. It’s such a small volume I don’t want to overpressurize it, but that’s just an intuition not experience.

I’ll stick a camera on the sustainer to be able to watch each event afterwards.

(Edit: whoops just saw this wasn’t responding to me, sorry)

 

[Banzai88]

I just did a pop test of a small interstage similar to this, 5 inch long, 2.6” diameter coupler closed on one end, motor sticking half way into it. It was my first time testing BP charges, so this might be old news to others, but one thing is that the online calculators gave such a small amount of BP that it may not have worked with my containment strategy (centrifuge vial, hole drilled in the bottom for ematch). Since the ematch sticks up a bit from the bottom of the tube, the recommended amount wouldn’t have covered the sparky bit. A buddy recommended I add enough to cover it, even though that was double or more what the calculator said. It worked fine at about 0.5g. Just a heads up in case you haven’t tried small charges.

I’ve also gone a bit wild with the vinyl cutter on it! Planning to test at the Jan 20 CMASS launch.

The secret to getting tiny amounts to work is to pull the ematch head through the vial, fold the wire over so the pyrogen is now facing the V of the bottom of the vial, and then slide the vial up and seal the hole.

The goal is to place the pyrogen in the top 1/3 to 1/2 way thorough the powder charge. That's why using a tiny blob of hot glue to secure the wire is so convienent.....it allows you to get a final position on the match head as it cools. Use low temp and it's easier than high temp hot glue.

Fill any voids with a pinch of dog barf.

Some folks glue the cap on as an additional measure to develop pressure and ensure full burn of the charge.