First Electronic Staging - MPR Build

[cerving]

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

I use both... if you can, use the electronic deploy as the primarys and set the motor delay long as the backup. Aerotech delays tend to run a few seconds short, CTI's run just about as spec'ed.

 

[Buckeye]

I use both... if you can, use the electronic deploy as the primarys and set the motor delay long as the backup. Aerotech delays tend to run a few seconds short, CTI's run just about as spec'ed.

For sure. I do this on all my HPR. I am just thinking about mass and complexity creep into this MPR design.

 

[cerving]

For sure. I do this on all my HPR. I am just thinking about mass and complexity creep into this MPR design.

LOL, that's a problem with ALL projects...

 

[Buckeye]

Do you shear pin the ISC to the booster?

OK, I answered my own question. Shear plates added to the booster/ISC interface with #2-56 tapped holes.

I got an assortment pack of brass shims from Amazon. 0.004" thickness used here for the booster to ISC shear plates (cardboard to cardboard). 0.008" used for the payload to nose cone shear plates where there is more clearance (cardboard to plastic). No carving out a recess needed. Only the female end of the interface gets the plates. Affixed with CA.

 

[Buckeye]

Here are the brains of the operation. Raven4 and PowerPerch on one side of the sustainer av-bay sled. On the other side is a screw switch with cover as an additional arming switch for the sustainer motor igniter. This switch will be closed as the last step on the pad.

The downside of my electronics setup is that I have 3 different switches needing 3 different tools! Hex key for the Fingertech in the booster, magnet for Raven, and Phillips screwdriver for the redundant sustainer igniter switch.

 

[kjhambrick]

Here are the brains of the operation. Raven4 and PowerPerch on one side of the sustainer av-bay sled. On the other side is a screw switch with cover as an additional arming switch for the sustainer motor igniter. This switch will be closed as the last step on the pad.

The downside of my electronics setup is that I have 3 different switches needing 3 different tools! Hex key for the Fingertech in the booster, magnet for Raven, and Phillips screwdriver for the redundant sustainer igniter switch.

View attachment 625095View attachment 625094

What a Nice, Roomy Sustainer AV-Bay, @Buckeye !

Do you also have some sort of hold-down to keep your Power Perch LiPo Battery from sliding laterally at the free-end ?

Or is the stack of Plywood squares tight enough that the battery can't slip sideways ?

I've settled for tape but I an looking for something a little more elegant

I feel your pain on the tool set

I don't need a Hex Key ( yet ) but maybe I do ...

Sorry if I missed it above, what is the Fingertech ?

Thanks !

-- kjh

 

[Buckeye]

What a Nice, Roomy Sustainer AV-Bay, @Buckeye !

Do you also have some sort of hold-down to keep your Power Perch LiPo Battery from sliding laterally at the free-end ?

Or is the stack of Plywood squares tight enough that the battery can't slip sideways ?

I've settled for tape but I an looking for something a little more elegant

I feel your pain on the tool set

I don't need a Hex Key ( yet ) but maybe I do ...

Sorry if I missed it above, what is the Fingertech ?

Thanks !

-- kjh

Thanks.

The axial force of the battery connector on the Perch plus the normal force of the top cover is usually enough to prevent any battery movement.

Fingertech switch shown in post #49. I have not used these before, but the flat profile and arming screw on the side should work well for the pancake booster av-bay.

 

[kjhambrick]

Thanks.

The axial force of the battery connector on the Perch plus the normal force of the top cover is usually enough to prevent any battery movement.

Fingertech switch shown in post #49. I have not used these before, but the flat profile and arming screw on the side should work well for the pancake booster av-bay.

Thanks again, @Buckeye !

So that's what the upside-down 'Amazon-Smiley-Looking-Thingie' is -- a FingerTech Mini Power Switch

I'll have to check them out !

--kjh

 

[Buckeye]

Do you also have some sort of hold-down to keep your Power Perch LiPo Battery from sliding laterally at the free-end ?

On second thought, this is a good idea. The battery does wiggle side-to-side a bit. I will add a another "wall" to prevent lateral motion.

 

[David Schwantz]

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.

I like the vials myself. I have used as small as .4 grams. Instead of drilling hole in bottom I like to slot the vial right under the lid with a dremel tool. This way the wire has a tight fit so both the slot and lid hold it in place. As Banzai88 said put match into BP. I then use dog barf on top of BP in the void. I also tape of the top with 2 strips of yellow masking tape and one around the middle. Not only does this help contain BP charge but it also holds wire to vial.

 

[David Schwantz]

Your Av Bay does look very nice. But if I may ask about the plastic all thread, are you sure it is up to the task?

 

[Buckeye]

Your Av Bay does look very nice. But if I may ask about the plastic all thread, are you sure it is up to the task?

Good question. Nylon all-thread has been discussed and used before by others. l almost used it on a HPR Wildman Mach 2 fiberglass av-bay, but I chickened out in the end.

This is a MPR made of cardboard, so mass is much less. I plan on some vigorous ground testing of deployment charges to give a good yank of the recovery harness.

50-100G is the rule of thumb shock loads. I am using #10-24 nylon all-thread. Isn't there a thread somewhere that gives the tensile strength of various model rocketry materials?

 

[kjhambrick]

Your Av Bay does look very nice. But if I may ask about the plastic all thread, are you sure it is up to the task?

I can't say either way, @David Schwantz ...

Good question. Nylon all-thread has been discussed and used before by others. l almost used it on a HPR Wildman Mach 2 fiberglass av-bay, but I chickened out in the end.

This is a MPR made of cardboard, so mass is much less. I plan on some vigorous ground testing of deployment charges to give a good yank of the recovery harness.

50-100G is the rule of thumb shock loads. I am using #10-24 nylon all-thread. Isn't there a thread somewhere that gives the tensile strength of various model rocketry materials?

@Buckeye --

I didn't know about that 'strength of materials' thread but now I'll go look for it ...

OTOH, You made me look when you mentioned upstream that you were using Nylon threaded rods ...

McMaster does not list the tensile strength of their 10-24 Nylon threaded rod ...

Grainger only carries #10-32 Nylon threaded rods.

But they do list the tensile strength of their 10-32 Nylon threaded rod as 12,000 psi: Fully Threaded Rod: #10-32 Thread Size, Nylon, 6/6, Plain, 2 ft Overall Lg, #10 Thread Size Broad

So given that the minor diameter of a #10 screw is 0.1404 inch, the cross-sectional area would be 0.0155 in^2.

So the breaking force of a single #10 Nylon threaded rod would be OOO 186 lbf.

For comparison, a 316 stainless steel(*) #10 threaded rod is listed at 70,000 psi so a single #10 rod would break at around 1,084 lbf.

YMMV ...

One thing I wonder about threaded rods is whether the threads in a threaded rod could serve as stress concentrators ...

But I would feel OK connecting to two -or- three lbs of 'stuff' and a 50-G ejection charge shock load with two Nylon rods in one of my rockets ...

-- kjh

(*) unworked 316 stainless steel is austenitic and is therefore non magnetic.

In my recent tests with the Featherweight Mag Switches and AV-Bays, #2-56 316 SS rods are not attracted by a magnet and do not affect the operation of the mag switches any if at all.

 

[Buckeye]

Good investigation, @kjhambrick! I also went searching last night and found 12,000 psi for nylon 6/6 as well. Also, this webpage:

https://www.plasticnutsandbolts.com/mechtech.html
shows #10-24 machine screws with 139 lb yield/149 lb break. Let's say 278 lbs will be the limit of 2 threaded rods holding the bay.

My sustainer should be no more than 1 kg (2.2 lbs). 220 lbs at 100G. So, I think I will be OK, as you indicated.

I am not worried with affecting the FW magnet switch. I am looking at the nylon rods for mass savings and just curiosity.

 

[bad_idea]

The problem I had with nylon allthread when I tried it was it stretching and loosening fasteners as a result. I was only using M3 though. I've wondered if it wasn't worth another try with thicker, stouter nylon.

 

[Buckeye]

Securing the sustainer av-bay to the payload.

Two (2) #6 screws used to hold the av-bay. When using T-nuts, I usually grid off the excess length. Instead, this time I made little wood spacers, since I have plenty of room in the av-bay. The spacers are contoured to the ID of the coupler. The T-nut is super-glued to the spacer.

 

[cerving]

Good investigation, @kjhambrick! I also went searching last night and found 12,000 psi for nylon 6/6 as well. Also, this webpage:

https://www.plasticnutsandbolts.com/mechtech.html
shows #10-24 machine screws with 139 lb yield/149 lb break. Let's say 278 lbs will be the limit of 2 threaded rods holding the bay.

My sustainer should be no more than 1 kg (2.2 lbs). 220 lbs at 100G. So, I think I will be OK, as you indicated.

I am not worried with affecting the FW magnet switch. I am looking at the nylon rods for mass savings and just curiosity.

You'd need a 3/8" Nylon bolt to get the same strength (around 1000#). All in all, you probably won't end up saving much weight, if any... stick with the 10-24 steel allthread. You don't have any radios in the AV bay so there's no reason not to.

 

[David Schwantz]

Buckeye, I also make little square spacers for my blind nuts. I use the ones with the little Anti rotation tabs. I make my ply oversize and use 5 min goobered on top to hold them in place.

 

[Buckeye]

I am still here, finishing up the electronics bay.

I just watched @JimJarvis50 presentation about staging techniques and safety at NARCON 2024. Excellent talk for a newbie like me with lots of good advice for any electronic-staged rocket. I will be using some of his methods.

 

[dasein668]

I am still here, finishing up the electronics bay.

I just watched @JimJarvis50 presentation about staging techniques and safety at NARCON 2024. Excellent talk for a newbie like me with lots of good advice for any electronic-staged rocket. I will be using some of his methods.

Is this presentation available online?

 

[Buckeye]

Is this presentation available online?

If you paid for vNARCON 2024, you can still watch the virtual event. Else, it will show up on YouTube in a few months.