Motor design questions, where do they go?

I'm part of a team at school designing a solid motor. I'm part of the team that is designing the casing. Its going to be a snapring casing. But where can I ask questions or find sources that will help me designing a motor with an operating pressure of ~500 psi.
Things i would like to learn: wall thickness required, snap rings to use, designing o-ring groove, nozzle retention, and (forward?) closure retention.

I hope this isn't a question for the restricted forumn

I don't want to get into specifics, but why not use a commercial off the shelf motor case? Unless you're sitting around with a lathe and nothing to do, it would probably be cheaper?

Where are you located, and what size (H, J, etc) motor are looking to fly?

At the very least you could document why you're not just buying a Loki or other commercial case ( e.g. our budget is X but we have a bunch of free machine time and student hours ).

2059097 said:

I'm part of a team at school designing a solid motor. I'm part of the team that is designing the casing. Its going to be a snapring casing. But where can I ask questions or find sources that will help me designing a motor with an operating pressure of ~500 psi.
Things i would like to learn: wall thickness required, snap rings to use, designing o-ring groove, nozzle retention, and (forward?) closure retention.

I hope this isn't a question for the restricted forumn

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Do you have a Tripoli Rocketry Association mentor with experience designing and building rocket motors? You should not have to ask these questions anonymously here if you have a good mentor.

Without knowing more about you, your school, and your project, people will be reluctant to give you help.

jsdemar said:

Do you have a Tripoli Rocketry Association mentor with experience designing and building rocket motors? You should not have to ask these questions anonymously here if you have a good mentor.

Without knowing more about you, your school, and your project, people will be reluctant to give you help.

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This is good advice.

Find a local NAR or TRA club, visit, and find experienced, knowledgeable, mentors who can answer your questions and walk you past potential pitfalls in your thinking, mathematics, etc.

But as far as your original question goes, your best bet on this forum for questions in this particular area would likely be in the "Propulsion" forum. Bear in mind however, that once you start asking questions about formulae for your fuel, then your questions will be moved to the "Research" forum and you won't be able to go there unless you hold an "L1" high power certification from either NAR or TRA and are a United States citizen.

Hope that helps.

djs said:

I don't want to get into specifics, but why not use a commercial off the shelf motor case? Unless you're sitting around with a lathe and nothing to do, it would probably be cheaper?

Where are you located, and what size (H, J, etc) motor are looking to fly?

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Well we have a rocketry club of atleast 120 members and about 4 different competition teams within this club. sometimes it is kind of hard to give important work to people, So I'm forming a team to learn about designing casings. We have a couple of members who have manufacturing experience who would manufacture the hardware .
So, we want to learn to calculate stress for the sake of learning to do so.

We typically use COTS motors and casings but recently we have started EX motors . Our goal for the year is to test and fly an I/J AP and an L/K sugar . We fly at FAR in California.

Well we have a mentor(sugar shot) . but often I feel like we rely on him too much and think we should only ask him things after not finding the answers elsewhere.

2059097 said:

Well we have a mentor(sugar shot) . but often I feel like we rely on him too much and think we should only ask him things after not finding the answers elsewhere.

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If your mentor is Rick M- he's on this forum (HighDesertRocketry) and is generally a really good guy.

Some of the info you're asking can be had from the mechanical engineering bible "Machinery's handbook". it'll list specs for snap rings, O rings, backing sizes for O-rings, etc..

2059097 said:

Well we have a rocketry club of atleast 120 members and about 4 different competition teams within this club. sometimes it is kind of hard to give important work to people, So I'm forming a team to learn about designing casings. We have a couple of members who have manufacturing experience who would manufacture the hardware .
So, we want to learn to calculate stress for the sake of learning to do so.

We typically use COTS motors and casings but recently we have started EX motors . Our goal for the year is to test and fly an I/J AP and an L/K sugar . We fly at FAR in California.

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Not enough information. Which school? What is your real name? What is your certification level?

If you are a college student in Engineering, you should already have access to older students or professors who can help you calculate the required case thickness for the hoop strength needed. If you have to, use Google... there are many resources for such calculations. A model rocketry forum should be your last resource.

But ... but ... I read it on the Internet!

Bat-mite said:

But ... but ... I read it on the Internet!

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if I wanted childish replies i would have posted on YouTube

2059097 said:

if I wanted childish replies i would have posted on YouTube

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The folk here are looking to help you but also to steer you away from potential trouble (for you as well as for our hobby). Please understand that, for the most part, comments like this are intended to make a point and are given in a spirit of helpfulness. Please accept them in that spirit. But even if they aren't please don't antagonize your critics. Doing so will draw worse criticism and chase away the very people whose help you need.

My name is............I'm with ............high school/college. We've been competing in the following Rocketry events..club launch, ESRA, SLI etc. Up to this point we've been working with the guys out at FAR. Maybe some of you know Rick? We're interested in getting into Research Rocketry. We want to start out small with a 38mm motor. At this point we are looking for help in deciding on what materials to use for this size of snap ring motor case for up to 500 psi (at this point, those that can answer your questions, know your not ready to make a motor case, unless you forgot the 1 as in 1500psi).

#389287

Things can and do go wrong.

https://www.rocketryforum.com/showthread.php?140120-University-of-Idaho-Rocket-Accident

Peartree said:

The folk here are looking to help you but also to steer you away from potential trouble (for you as well as for our hobby). Please understand that, for the most part, comments like this are intended to make a point and are given in a spirit of helpfulness. Please accept them in that spirit. But even if they aren't please don't antagonize your critics. Doing so will draw worse criticism and chase away the very people whose help you need.

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As John wrote, I am not trying to be sophomoric. I am trying to point out that maybe the Internet isn't the place to go for this kind of information. Someone may get on and tell you, very confidently, exactly what you need. but who is that person? Do you know him? How do you know he isn't some faker posting from a mental ward?

Yes, very bad things do happen when people experiment with rocket fuel. That is not meant as a discouragement. Rather it is to impress upon you the need to learn from an expert that you know and trust.

I believe that your mentor would much rather work with you personally than find out you are getting information online from people you don't know.

At the very least anything you find yourself from a non verifiable source, run by your mentor. "I found these equations and here are my results. Does this look correct?"

Sent from my HTC6535LVW using Rocketry Forum mobile app

2059097 said:

if I wanted childish replies i would have posted on YouTube

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Now you know why I said this should be the last place you come for these questions.

The Internet has very useful resources if you qualify what you find. For example:
https://www.engineersedge.com/calculators.htm

The guys at FAR would be more than willing to help you, that would be a great point of contact, not only are they a licensed motor manufacturer but regularly run classes in motor making and to get certified as a pyrotechnician. In California you need to either have a California Pyrotechnic License Class 2 or work under the supervision of someone who possesses one to make your own motors.

tfish said:

My name is............I'm with ............high school/college. We've been competing in the following Rocketry events..club launch, ESRA, SLI etc. Up to this point we've been working with the guys out at FAR. Maybe some of you know Rick? We're interested in getting into Research Rocketry. We want to start out small with a 38mm motor. At this point we are looking for help in deciding on what materials to use for this size of snap ring motor case for up to 500 psi (at this point, those that can answer your questions, know your not ready to make a motor case, unless you forgot the 1 as in 1500psi).

#389287

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I said operating pressure. There would be a factor of safety applied

dr wogz said:

Some of the info you're asking can be had from the mechanical engineering bible "Machinery's handbook". it'll list specs for snap rings, O rings, backing sizes for O-rings, etc..

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Thanks! I'll definitely be using this