Cluster vs Large Motor...

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lakeroadster

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I have been contemplating this question for quite a while, and after just seeing a post regarding a member's first flight of an Estes Patriot using 4 D-motors... well, I just have to ask... WHY?

Why would you build a rocket using clusters vs a single larger motor of equivalent (or better) total impulse power? Why risk one or more of the motors in a cluster not igniting before the remainder shove it off of the pad? Why deal with the complexity of a cluster vs reliability of a single larger motor? Why deal with the COST of a cluster vs a single larger motor?

Not trying to be critical of ANYONE who chooses to fly cluster models; I'm just trying to learn about an area of model rocketry that I have never ventured into. I've flown single-motor models most all of my life, including up to G76 AeroTech RMS motor systems, but never a cluster.

Thanks!
Clusters enable a designer to come up with some really innovative designs that have motors in multiple locations, sometimes even up near the top of the rocket for tractor motor designs.

One big motor... is always going to be... on the rocket c/l at the very bottom of the rocket.... yawn.
 

CoyoteNumber2

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well, I just have to ask... WHY?
The same reason people do boost gliders, oddrocs, minimum diameter, multistage, night launches, drag races, fat rockets, skinny rockets, tube fins, monocopters, upscales, downscales, kits, clones, scratch-built, and any other type of rocket I have neglected to mention.
 

DabCat

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Curious about your interchangeable motor mounts - how are they designed and held in place?
The centering rings aren't glued in. There is a ring glued in at the top of the centering ring which acts as a stopper. The motor mount is screwed into the body tube. I can send some pictures when I get home if that explanation was a bit confusing.
 

3stoogesrocketry

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Clusters allow you to reach a safe thrust to weight ratio and gives you extra rail speed if the one large motor does not have sufficient thrust.
 

BigMacDaddy

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The centering rings aren't glued in. There is a ring glued in at the top of the centering ring which acts as a stopper. The motor mount is screwed into the body tube. I can send some pictures when I get home if that explanation was a bit confusing.
FWIW -- if you did this with 3D printed parts you could make the mount twist to lock in (you could actually do this with traditional building methods also but a bit more complex).

This is more or less what I did with my R1 rocket... could swap out this 2-engine setup with a single engine or 3x engine cluster...

1634760179141.jpeg
 

DabCat

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FWIW -- if you did this with 3D printed parts you could make the mount twist to lock in (you could actually do this with traditional building methods also but a bit more complex).

This is more or less what I did with my R1 rocket... could swap out this 2-engine setup with a single engine or 4x engine cluster...

View attachment 486534
I didn't think of that. That's a really good idea. Thanks for sharing!
 

Lee

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The centering rings aren't glued in. There is a ring glued in at the top of the centering ring which acts as a stopper. The motor mount is screwed into the body tube. I can send some pictures when I get home if that explanation was a bit confusing.
Please do
 

kramer714

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Why...? Geek Masochism that's why

I did a cluster of 19E Estes for a total of 516ns - Middle sized I motor equivalent, sure, could have just bought an I motor, sure it would have been easier, sure it would have been cheaper, way easier to light (they all ignited - no cato), but what is the challenge in that.

Hardest cluster, 2 hybrid RATT, ultimate geek masochism, and the loudest thing I have ever heard at a rocket launch.
 

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6inchmonster

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FWIW -- if you did this with 3D printed parts you could make the mount twist to lock in (you could actually do this with traditional building methods also but a bit more complex).

This is more or less what I did with my R1 rocket... could swap out this 2-engine setup with a single engine or 3x engine cluster...

View attachment 486534
What are you printing with there? I have to imagine a cheapo printer with sugar plastic not holding up to much, but dunno
 

BigMacDaddy

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What are you printing with there? I have to imagine a cheapo printer with sugar plastic not holding up to much, but dunno
Printing with ABS plastic which has done quite well with my engine mounts, retainer caps, etc... (although I have not yet launched this cluster so it might eject itself from the rocket if the 3D printed parts to do hold up). Not as worried about the thrust since the internal body tube conveys much of the force directly through to the sustainer portion.
 

jqavins

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All the things about it's fun (because it's cool, a challenge, good looking, etc.) and for one practical reason that's only been touched on: it creates the opportunity to make novel thrust curves by adding up the smaller existing ones.

Let's say I've got a heavy LPR that flies well on a D12, but I want a really low flight. I can't just use a C6 instead, because I won't get enough speed off the rod. But I can use a pair of B6s; combined they have about the same average thrust as a D12, similar peak thrust (a little less) and only half the total impulse. It's like having a fast burn C, but there are no fast burn Cs that will do the job for me, so I make one out of two Bs.

There are plenty of other scenarios one could think of where piecing together a custom thrust curve from standard parts could be beneficial. 1×F15 + 2×C5 comes to mind as probably good for something.
 
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6inchmonster

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Printing with ABS plastic which has done quite well with my engine mounts, retainer caps, etc... (although I have not yet launched this cluster so it might eject itself from the rocket if the 3D printed parts to do hold up). Not as worried about the thrust since the internal body tube conveys much of the force directly through to the sustainer portion.
I love ABS. What kind of printer (enclosure?) are you using? How concerned are you about fumes?

I have a cloth/pyro tent over a cheesy metal frame and I print in semi-outdoor space. It does ok, not as easy as other filaments but the end result is that I do not worry about the printed parts while they are in use.
 

dman007

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Here is my contribution to this thread. Flying on a tri cluster of D12-7 motors. Made it safely up and down from 700'. The sim said 900'.
wingedTiger.jpg
 

Rocketjunkie

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At the time the Estes Patriot came out, the largest Estes motor was the D12. It needed 4 for a decent flight. (You could always put in a 29 mm mount and nose weight.)
 

BigMacDaddy

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I love ABS. What kind of printer (enclosure?) are you using? How concerned are you about fumes?

I have a cloth/pyro tent over a cheesy metal frame and I print in semi-outdoor space. It does ok, not as easy as other filaments but the end result is that I do not worry about the printed parts while they are in use.
I have a Prusa Mk3s in an Ikea Lack table enclosure w/ acrylic sides & doors + plywood bottom (not totally sealed around the doors but pretty well sealed off from the room). I have not worried about fumes (there is little to no smell when I am printing -- although I know that is not a great indicator) and no one is near the unit usually when it is printing. After a little bit of research I realized I should probably think more about this - I also need to move my power supply out of the enclosure so that it does not overheat.
 

Cape Byron

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Clusters of any size are great! Nothing to do with smaller motors. It's just fun. And isn't that what the whole hobby is about?

P1230222 (FILEminimizer).JPG


Two-Up proto on 2x A3-4T.
 

heada

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Staged clusters is where its at!

I have a 3x 24mm staged to a 3x24mm in a 3" rocket.

3x E12-0 to 3x E12-8

Why? Because its fun and this is a hobby.
 

Mike Haberer

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Why? It's a personal preference and decision. It's a challenge. Clusters make a lot of noise, flame and smoke. Successes are more rewarding. Failures are more educational (and spectacular).

And then they is the ultimate answer. Why not?
 

Rocketjunkie

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Clusters are just for fun. This is a hobby and the purpose is to have fun. I have LOC Ultimates scaled for 13, 24, 29, and 38 mm motors. Need to build one for 18 mm motors and 10.5 mm motors as I still have a bunch of them.
I've been flying my Motoreater design (54 & 8 29 mounts) for over 30 years and it has about 80 flights on it.
 

BigMacDaddy

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I posted this in the Half Baked Design thread but figured I should share here since this conversation motivated me to try a bigger cluster (likely not the OP's purpose to inspire more insanity). Leonora Christine from the book Tau Zero (artist rendition for cover of reprint). The cluster here would be a design element to match the prototype so thinking I could try to do this with 8x 13mm mini engines in that middle portion and one 18mm engine all the way in the back. Would cost just shy of $15 to launch it.

1634925937728.png
 
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Five

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Especially when one doesn't light and the rocket goes sideways.

same thing happened to me. Only one ignited and went sideways. I wasn’t able to retrieve the rocket, so not only did lose a rocket but I also lost two good motors.
 

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teepot

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I like clusters for the variety of designs options. I can get creative. And all the flame and smoke isn't bad either.
20211022_111316[1326].jpg
20211022_111347[1327].jpg
20211022_111435[1328].jpg
 

Joekeyo

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Staged clusters is where its at!
Is this compatible with the NAR safety code? There is some controversy.

I like clusters because I like to see how close I can get to making a paperclip into a round ring, then twisting the tiny ignitor wires around it.
 

heada

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Is this compatible with the NAR safety code? There is some controversy.

I like clusters because I like to see how close I can get to making a paperclip into a round ring, then twisting the tiny ignitor wires around it.
What part would run afoul of any safety code? Clustering or staging or staging clusters? All have been done 100% within the NAR safety code.
 

smstachwick

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Is this compatible with the NAR safety code? There is some controversy.
An E12 has 36g of propellant. 6x36g=216g. Maxmimum for a model rocket per the NAR Model Rocket Safety Code is 125 grams.

That’s not to say it’s dangerous or illegal though. Assuming competent design, it’d be just as safe as any other cluster/multistage and it’d be perfectly legal to fly with a L1 HPR certification and an FAA waiver for the expected altitude, along with being in compliance with any other relevant regulations.
 

heada

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An E12 has 36g of propellant. 6x36g=216g. Maxmimum for a model rocket per the NAR Model Rocket Safety Code is 125 grams.

That’s not to say it’s dangerous or illegal though. Assuming competent design, it’d be just as safe as any other cluster/multistage and it’d be perfectly legal to fly with a L1 HPR certification and an FAA waiver for the expected altitude, along with being in compliance with any other relevant regulations.
I'm L2 certified and fly that config at launches with a waiver. It's no different than when I launch my LOC Ultimate with 6x F42 and 1x H180. Combined they're in the J range so you have to be L2 certified but nothing about either is outside of safety rules.
 
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