First Electronic Staging - MPR Build

[Buckeye]

This thread will document my build of a mid-power 2-stage rocket. I will probably need some help along the way. These are my goals/key points:

• Learn 2-stage with 29mm motors, maybe 24mm in the sustainer. 29/180 is probably the longest I would ever use.
• 2500 feet or so altitude to start so that I can see all the events
• Utilize 3" diameter lightweight cardboard airframe (BMS)
• No electronics in the booster. Motor eject
• Raven4 in the sustainer: Separation charge, sustainer ignition, sustainer apogee, sustainer main

I will bash together two 29mm School Rockets from Balsa Machining.



Here is a quick Rocksim for the general layout and profile:

 

[Buckeye]

I purchased some additional couplers and bulkheads from BMS. However, the 3" couplers don't fit in the 3" tubing. The coupler O.D. is the same as the airframe I.D., so no clearance. Weird. I ordered the red couplers from Apogee which are slightly smaller and fit nicely. I got some longer motor tubes, too. I will probably cut off some circumference of the BMS couplers and use them as stiffy tubes.



Now, the BMS coupler bulkheads are too big for the Apogee coupler. I bolted them all together and carefully rotated them against my sander to turn them down to the right diameter.



Fins were sealed with Bondo Spot Putty and sanded. All edges are rounded. Ugh, I hate working on fins. Now I have 8 of them to deal with!

 

[bad_idea]

I purchased some additional couplers and bulkheads from BMS. However, the 3" couplers don't fit in the 3" tubing. The coupler O.D. is the same as the airframe I.D., so no clearance. Weird.

I've always gotten BMS 3" coupler to work as a fixed part by burnishing the ends of both it and the tube in opposite directions and lubricating with epoxy. As a sliding part, I've sometimes had to sand it quite a lot. I have a floating 3" avbay that's a PITA to position; someday when I have the time, I'm going to harden the whole thing with CA and sand it down a whole lot more (something I should have done when I built it).

 

[NTP2]

Fins were sealed with Bondo Spot Putty and sanded. All edges are rounded. Ugh, I hate working on fins. Now I have 8 of them to deal with!

I feel you, I kind of like sanding fins but I hate the sanding of body tubes.

 

[waltr]

I also used two BMS kits to build a 2-stage.
I added a Stuffer tube to the sustainer MMT then built an ebay into the side just above the MMT.
To get an ISC into the sustainer I moved the sustainer fins forward.
The Booster is a very simple motor ejection recovery.
The ISC coupler was coated with thin CA then sanded very smooth. TheISC is a simple couple with a bulk-head and eye bolt.

How are you doing the ISC?

Looks like you have the electronics forward, just below Nose cone. How are you running sustainer separation and ignition wires?

 

[kjhambrick]

I also used two BMS kits to build a 2-stage.
I added a Stuffer tube to the sustainer MMT then built an ebay into the side just above the MMT.
To get an ISC into the sustainer I moved the sustainer fins forward.
The Booster is a very simple motor ejection recovery.
The ISC coupler was coated with thin CA then sanded very smooth. TheISC is a simple couple with a bulk-head and eye bolt.

How are you doing the ISC?

Looks like you have the electronics forward, just below Nose cone. How are you running sustainer separation and ignition wires?

Yes !

I am an AV-Bay plagarist and I too want to fly a 2-stage rocket someday soon.

Please post some pics of your electronics when you are ready !

Thanks @Buckeye and good luck !!

-- kjh

 

[NTP2]

I am an AV-Bay plagarist

We are ALL av bat plagarists.

 

[Buckeye]

How are you doing the ISC?

Looks like you have the electronics forward, just below Nose cone. How are you running sustainer separation and ignition wires?

The ISC will simply be a coupler with a bulkplate.

I am envisioning a conduit of 1/4" launch lug to run the wires with a break-away of some sort.

 

[Buckeye]

I worked on the easy part, first. The booster. I decided on 15" length, just enough for longest motor and recovery gear. I opted for the Estes 29mm motor retainers.

 

[plkap74]

Totally new to staging, but I was sketching up designs for something similar, using the LOC Graduator and an extra set of fins and an extra body tube. What goes into consideration of using a separation charge vs just lighting the second stage motor and having that separate the stages?

Here is what I've got so far, including a passthrough (drinking straw?) for igniter wires.

 

[Buckeye]

Totally new to staging, but I was sketching up designs for something similar, using the LOC Graduator and an extra set of fins and an extra body tube. What goes into consideration of using a separation charge vs just lighting the second stage motor and having that separate the stages?

Here is what I've got so far, including a passthrough (drinking straw?) for igniter wires.

The separation charge is more elegant and can be configured for the optimum time to drop off the spent booster mass. Also, the second stage motor ignition can really toast the booster and interstage coupler. The separation charge is very small and won't damage anything.

 

[Buckeye]

Here is what I've got so far, including a passthrough (drinking straw?) for igniter wires.

Yeah, I am thinking the same thing using the 1/4" tubes that are used to package igniters in HPR reloads. I may run the conduit much longer forward, nearly to the bottom of the av-bay. I would glue it to the inner wall of the sustainer airframe.

 

[waltr]

Check the conduit ID with two pairs of ematch wires to ensure they fit.

I use a long piece of 1/4inch ID Launch lug tubing.
Since my igniter tube run into the Altimeter bay I need to plug the tube where it exists at the motor. Otherwise, separation hcrge can increase the pressure the baro sees which looks like going past apogee...

 

[plkap74]

I wonder what I could use to prevent the second stage from roasting the inside of the cardboard coupler I’m using for the inter stage

 

[waltr]

I first used sustainer ignition to separate stages. This worked and didn't fry the ISC. However, biggest motor was a 24mm D15.
I did give the inside of the upper end of the ISC a thin coat of epoxy. It held up.

Bigger motors will have more fire so YMMV.

 

[Banzai88]

I wonder what I could use to prevent the second stage from roasting the inside of the cardboard coupler I’m using for the inter stage

Coat it with a layer of JB weld

 

[bobbyg23]

Only crazy people do 2 stage rockets

 

[Jmhepworth]

I wonder what I could use to prevent the second stage from roasting the inside of the cardboard coupler I’m using for the inter stage

You really do want a separation charge. That way you can dump the booster right after motor burnout and you don’t risk the sustainer motor destroying the interstage coupler. You want to dump the booster as soon as possible. The additional mass doesn’t compensate for the additional drag.

 

[bobbyg23]

I wonder what I could use to prevent the second stage from roasting the inside of the cardboard coupler I’m using for the inter stage

I do drag separation with a small charge for a backup.

 

[David Schwantz]

To all that hate sanding, try this

https://www.amazon.com/BLACK-DECKER...hvlocphy=&hvtargid=pla-4584001418770249&psc=1

 

[cerving]

To all that hate sanding, try this

https://www.amazon.com/BLACK-DECKER...hvlocphy=&hvtargid=pla-4584001418770249&psc=1

My kids got me one of those for Christmas a few years ago, it works amazing for sanding fins and fillets after you fill them. Way better than a sanding block, and 1/10 of the effort.

 

[David Schwantz]

I have worn out a dozen or so over the years. The best one was a Craftsman, but sadly no longer made
They do work great for fillets. I will put the paper on off center so it goes up and around the edge, this way it forms a rolled up sanding edge. Great for concave corners.

 

[kalsow]

I have worn out a dozen or so over the years.

That sound's about right. I'm on my 3rd or 4th one and David's rockets are at least 3x prettier than mine!

 

[plkap74]

You really do want a separation charge. That way you can dump the booster right after motor burnout and you don’t risk the sustainer motor destroying the interstage coupler. You want to dump the booster as soon as possible. The additional mass doesn’t compensate for the additional drag.

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!

 

[waltr]

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!

Plastic cap on nozzle is all I have used. No issues.

Yes, think about sir starts but do a few full DD rockets and flights. There is enough tiny things to go wrong with DD and many more with air starts.

 

[Rocketclar]

I wonder what I could use to prevent the second stage from roasting the inside of the cardboard coupler I’m using for the inter stage

What I did for my LOC Terrier/Sandhawk was to paint the inside of the ISC with hi Temp paint and then stuff dog barf and wadding in since I thought I would get drag separation. After several flights with video looking down from the sustainer, I never got drag separation. I did capture some pictures of the dog barf getting blasted out. 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!

 

[Rocketclar]

Plastic cap on nozzle is all I have used. No issues.

Yes, think about sir starts but do a few full DD rockets and flights. There is enough tiny things to go wrong with DD and many more with air starts.

I just use Gorilla tape to hold in the starter for the sustainer motor. For my Terrier/Sandhawk, I use JLCRs for both the booster and sustainer. That keeps it simpler vs wiring for DD. Just remember to turn them on!

 

[Rocketclar]

Check the conduit ID with two pairs of ematch wires to ensure they fit.

I use a long piece of 1/4inch ID Launch lug tubing.
Since my igniter tube run into the Altimeter bay I need to plug the tube where it exists at the motor. Otherwise, separation hcrge can increase the pressure the baro sees which looks like going past apogee...

I, too, just used launch lug tubing. I glued a couple of pieces together. I run two Firewire leads down them. At my bulkhead which is just above the motor I seal both sides the wires go thru with hot glue.

 

[bobbyg23]

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!

No worries about the separation charge igniting the sustainer motor. And even if it did, that would be a bonus that your sustainer motor actually lit.

 

[David Schwantz]

Are you cutting a hole in the red cap?