38 mm Minimum Diameter Questions

[James Keller]

Hey all,
I'm in the process of making a minimum diameter 38mm and had a few questions, any help would be greatly appreciated. My first question is how to do a Nose Cone Av bay. I have an Eggtimer Quasar that handles both GPS and altimeter work. I am also going to be making a carbon fiber airframe so I can't put the Quasar in the Coupler like I've done in the past. So my question is can I do dual deployment with the electronics in the nose cone. Or is dual deployment necessary with that light of a rocket? Open Rocket suggests that it will be around 1.13lbs without the motor. Another question I had would be how few wraps can I get away with? I recently did 4 on a 3in rocket could I go 3 on a 38mm? And my last question since there won't be any electronics in the coupler I plan on putting a camera in there, is there a "proper" way of doing this? Should I use some sort of glass for the camera hole? The camera I plan on using is a Runcam Thumb. Any pictures or explanations would be a huge help.
Thanks,
James

 

[Seatechnerd83]

Hey all,
I'm in the process of making a minimum diameter 38mm and had a few questions, any help would be greatly appreciated. My first question is how to do a Nose Cone Av bay. I have an Eggtimer Quasar that handles both GPS and altimeter work. I am also going to be making a carbon fiber airframe so I can't put the Quasar in the Coupler like I've done in the past. So my question is can I do dual deployment with the electronics in the nose cone. Or is dual deployment necessary with that light of a rocket? Open Rocket suggests that it will be around 1.13lbs without the motor. Another question I had would be how few wraps can I get away with? I recently did 4 on a 3in rocket could I go 3 on a 38mm? And my last question since there won't be any electronics in the coupler I plan on putting a camera in there, is there a "proper" way of doing this? Should I use some sort of glass for the camera hole? The camera I plan on using is a Runcam Thumb. Any pictures or explanations would be a huge help.
Thanks,
James

FYI the runcam Thumb runs on 5v, and the buck converters for my 2S batteries had reverse polarity connectors so i had to switch the connector housing around on my runcam thumb, just make sure to look how the wires are going into the camera before actually powering it on. Also, you shouldn't need any sort of "glass" on the window unless youre worried about the vent hole causing extra drag and/or youre worried about the camera's wellbeing on landing.

 

[rocketace]

Just for a reference point. I have a 38mm min diameter was 3 layers of 3k CF twill airframe. Electronics in the nose cone, I’m doing dual deploy using a chute release, no drogue.

 

[James Keller]

FYI the runcam Thumb runs on 5v, and the buck converters for my 2S batteries had reverse polarity connectors so i had to switch the connector housing around on my runcam thumb, just make sure to look how the wires are going into the camera before actually powering it on. Also, you shouldn't need any sort of "glass" on the window unless youre worried about the vent hole causing extra drag and/or youre worried about the camera's wellbeing on landing.

Thanks, I definitely would have been very upset when I hooked my 2s directly to the camera and fried it.

Just for a reference point. I have a 38mm min diameter was 3 layers of 3k CF twill airframe. Electronics in the nose cone, I’m doing dual deploy using a chute release, no drogue.

Thanks for the response, what size chute is it?

 

[kramer714]

if you put the electronics in the coupler you can use the nosecone for head end dual deploy.

 

[James Keller]

if you put the electronics in the coupler you can use the nosecone for head end dual deploy.

The issue is my airframe is carbon fiber and the altimeter doubles as GPS telemetry so If I put it in the coupler I won't have any telemetry until the chute pops

 

[Sparkyflyer14]

Just for a reference point. I have a 38mm min diameter was 3 layers of 3k CF twill airframe. Electronics in the nose cone, I’m doing dual deploy using a chute release, no drogue.

How are you doing your chute release? Are you using a jlcr? I didn't think they fit in that small of tube.

 

[rocketman4h]

https://www.labratrocketry.com/shop
I use these products for my carbon Mongoose. the Eggfinder has to go in a fiberglass nosecone

 

[Highpowerrocketyahoo]

HED, Camera in the coupler. The NC FG?

 

[James Keller]

Ahhhh I see, I misunderstood what HED was and after some research that makes perfect sense. My next question however is the Nosecone that I have (Wildman VK Fiberglass) comes with a coupler preinstall coupler. How do you guys recommend dealing with this?

 

[rocketace]

Thanks for the response, what size chute is it?

18" or 24" depending on which rocket.

How are you doing your chute release? Are you using a jlcr? I didn't think they fit in that small of tube.

Very carefully. It is extremely difficult to get everything to fit just right. I have test assembled everything countless number of times. My only recommendation here is to pack it burrito style, very tight, and use baby powder. You can see some pictures here. JLCR in a 38mm tube

 

[mikec]

Ahhhh I see, I misunderstood what HED was and after some research that makes perfect sense. My next question however is the Nosecone that I have (Wildman VK Fiberglass) comes with a coupler preinstall coupler. How do you guys recommend dealing with this?

I have a Mach Mini with the same NC. I don't see any way you can do HED with that cone. I used a cable cutter with mine. https://ptrocketry.blogspot.com/p/store_28.html

Actually https://www.tinderrocketry.com/improved-piranha-line-cutter is probably a better source these days.

 

[robopup]

My standard number of layers on 38mm tube is 3 wraps of 6oz 3k plain weave carbon fiber (about 0.010 in per layer). I've gone as low as two, which I've hit pretty hard with a J570. The key when you go thin wall on tubes is to minimize the length of airframe tubing which is unsupported by the motor - mine has none, the nosecone sits directly on top of the motor which doubles as the coupler.

Electronics in the nosecone work great. Just make sure you understand your altimeter and how or whether it is using baro data. Here's a rocket I did last year which shows my standard rigging for dual deploy out of the nosecone. I've gone as small as 29mm and as large as 75mm. It has just a single ebay, no chute release or cable cutter.
https://www.rocketryforum.com/threads/75mm-composite-minimum-diameter-build.173626/

 

[James Keller]

Thanks for your responses

I have a Mach Mini with the same NC. I don't see any way you can do HED with that cone. I used a cable cutter with mine. https://ptrocketry.blogspot.com/p/store_28.html

Actually https://www.tinderrocketry.com/improved-piranha-line-cutter is probably a better source these days.

How reliable are cable cutters? It makes me slightly uneasy using one because I haven't ever done so.

My standard number of layers on 38mm tube is 3 wraps of 6oz 3k plain weave carbon fiber (about 0.010 in per layer). I've gone as low as two, which I've hit pretty hard with a J570. The key when you go thin wall on tubes is to minimize the length of airframe tubing which is unsupported by the motor - mine has none, the nosecone sits directly on top of the motor which doubles as the coupler.

Electronics in the nosecone work great. Just make sure you understand your altimeter and how or whether it is using baro data. Here's a rocket I did last year which shows my standard rigging for dual deploy out of the nosecone. I've gone as small as 29mm and as large as 75mm. It has just a single ebay, no chute release or cable cutter.
https://www.rocketryforum.com/threads/75mm-composite-minimum-diameter-build.173626/

I read through your thread and it was incredibly helpful, however I did have a little trouble conceptualizing how you kept the main from deploying when the dough does. Do you have a picture of it?

 

[robopup]

Here is the relevant image showing what the recovery harness looks like laid out. The key is that the kevlar that goes to the main parachute is longer than the kevlar that goes to the nosecone, and also that the main parachute packs tight. That was it should not rattle out until it's supposed to. I've tested this concept (very scientifically) by shaking vigorously with just the main packed as in an actual flight and could never get it to come out. I also have a few recoveries now from 20k-30k where it has all worked as expected.


And another picture from a new project with similar recovery setup with annotation of how things are packed (ignore the electronics on the right side of the picture):

 

[mikec]

How reliable are cable cutters? It makes me slightly uneasy using one because I haven't ever done so.

The cable cutter itself is quite reliable, but the recovery harness and wiring takes some care to avoid tangling. Using a "chute cannon" scheme similar to what robopup is using might be more reliable, but having tried it, it's hard to implement at this scale and has its own disadvantages. YMMV. Trying to jam all this stuff in a 38mm MD is just not easy.

In a chute cannon, the main is in a tube that's attached to the nose cone and generally has something that keeps it from being pulled out at apogee, like a small burstable/ejectable cover [edit: robopup just packs the main really tight, sounds like]. I'll let others who have made this work better than I speak to the details.

If you don't care about length, using conventional mid-bay dual deploy is unquestionably simpler.

 

[tfish]

Here's one way to setup reefed chutes..using a deployment sack and home made cutters.



Tony

 

[Grog6]

A competent technician should be able to add an external antenna for the gps function.

 

[Seatechnerd83]

It would probably be smart to 3d print a fin can that you glue onto a cardboard tube out of a plastic like ABS. then you're able to put an aerodynamic teardrop profile (speaking from experience from a G80 rocket that I built and flew) into thr fins, my G80 rocket was simming to 4500, if you thinned out the nosecone, glassed it with some low density fiberglass cloth, printed the fins out of ABS, made it with better processes, stuck an eggfinder mini/featherweight GPS and an eggtimer apogee in the nose, and made the fin profile more efficient than mine you might be able to get all the way up to 6k at most.

 

[Jeremy Sim]

Just for a reference point. I have a 38mm min diameter was 3 layers of 3k CF twill airframe. Electronics in the nose cone, I’m doing dual deploy using a chute release, no drogue.

Does a chute Release fit in a 38mm tube?

 

[mikec]

Even if a chute release fits, you're going to need something to deploy at apogee -- the longest available delays are too short for all but the smallest motors.

 

[James Keller]

Here is the relevant image showing what the recovery harness looks like laid out. The key is that the kevlar that goes to the main parachute is longer than the kevlar that goes to the nosecone, and also that the main parachute packs tight. That was it should not rattle out until it's supposed to. I've tested this concept (very scientifically) by shaking vigorously with just the main packed as in an actual flight and could never get it to come out. I also have a few recoveries now from 20k-30k where it has all worked as expected.
View attachment 583494

And another picture from a new project with similar recovery setup with annotation of how things are packed (ignore the electronics on the right side of the picture):
View attachment 583495

This was really helpful thank you. Now I just gotta figure out how to get it all to fit.

The cable cutter itself is quite reliable, but the recovery harness and wiring takes some care to avoid tangling. Using a "chute cannon" scheme similar to what robopup is using might be more reliable, but having tried it, it's hard to implement at this scale and has its own disadvantages. YMMV. Trying to jam all this stuff in a 38mm MD is just not easy.

In a chute cannon, the main is in a tube that's attached to the nose cone and generally has something that keeps it from being pulled out at apogee, like a small burstable/ejectable cover [edit: robopup just packs the main really tight, sounds like]. I'll let others who have made this work better than I speak to the details.

If you don't care about length, using conventional mid-bay dual deploy is unquestionably simpler.

I like that chute cannot idea, I have some ideas on how to do this without making it to heavy.

It would probably be smart to 3d print a fin can that you glue onto a cardboard tube out of a plastic like ABS. then you're able to put an aerodynamic teardrop profile (speaking from experience from a G80 rocket that I built and flew) into thr fins, my G80 rocket was simming to 4500, if you thinned out the nosecone, glassed it with some low density fiberglass cloth, printed the fins out of ABS, made it with better processes, stuck an eggfinder mini/featherweight GPS and an eggtimer apogee in the nose, and made the fin profile more efficient than mine you might be able to get all the way up to 6k at most.

I have a CNC router that I will be able to "airfoil" or more likely make a wedge shape with. I'm trying to push speed as much as possible so a wedge is the way to go I think.
Thanks for all of your guy's help, I will be sure to start a build thread once I get my parts and finalize designs.

 

[rocketace]

Does a chute Release fit in a 38mm tube?

Sure does, but its tricky. See my above post with the link.

 

[SolarYellow]

I have a CNC router that I will be able to "airfoil" or more likely make a wedge shape with. I'm trying to push speed as much as possible so a wedge is the way to go I think.
Thanks for all of your guy's help, I will be sure to start a build thread once I get my parts and finalize designs.

For a wedge shape, I like a conventional router with a router table. You can set it up so there are no multi-pass striations to sand off. The CNC router is still useful for cutting the fins out of whatever flat material you're going to start with.