vcp
Well-Known Member
A centering ring can be a really straightforward example to introduce you to how you can use CAD in your rocketry hobby. Many of you probably already have a favorite CAD program that you use, but if not, OpenSCAD is a program that is free, works on all platforms, and has a pretty gentile learning curve. You'll find it's not your usual type of interactive drawing system, but rather sort of a scripting system. Some people like this (I do), some don't; YMMV.
This example assumes you want to make a pair of centering rings, for a cluster model that incorporates 'focused thrust' as explained in the recent Apogee 'Peak of Flight' newsletter:
https://www.apogeerockets.com/education/downloads/Newsletter363.pdf
That article well explains the reasons for using angled motors, plus an in depth instruction on laying out the dimensions of centering rings for this purpose. While I'd certainly agree that it is useful to know how to lay them out this way (for post-apocalyptic modeling, got my slide rule and dial calipers ready), I think you'll find that the small effort in reading and understanding the following OpenSCAD file will be well worth it.
The attached file "FocusThrustCRs.scad" is just a text file; you can open it with any editor and take a look. It's extensively commented, and you can probably get the idea by just taking a look at it.
To open it as a CAD file, requires the installation of OpenSCAD, which is available here: https://www.openscad.org/index.html It's available for Win/Mac/Lin, and installs very easily. Documentation and tutorials are also available at that site.
Here are some snapshots of what you can get from that file. All of the parameters are easily adjustable to get whatever result you want. All you're doing is placing two flat disks, then placing and subtracting the motor tubes from those disks.
You'll find that OpenSCAD includes a rudimentary text editor that does the job (or you can use your favorite external editor if you want). After changing anything in the file, pressing F5, will recompile the image (Menu Design/Compile). When you have something you want, pressing F6 does a compile and render (Menu Design/Compile and Render (CGAL)); and from there you can do a Menu File/Export/Export as STL... An .STL file is a common format used by all 3D printers, and should be usable by CNC routers as well.
Once you're bending things with CAD, you'll find that centering rings don't have to be a flat bit of cardboard or ply anymore. This example adds a shoulder around the center tube to keep the ring perpendicular, pockets out most of the ring for weight savings, adds ribs for additional strength, fillets everything to avoid stress points, and serrates the outer and inner edges to aid gluing.
Have fun.
View attachment FocusThrustCRs.txt
Ah, I notice that RO doesn't allow files with obscure extensions. After downloading the file, change the extension to .scad so that OpenSCAD can find and read it.
Gary
This example assumes you want to make a pair of centering rings, for a cluster model that incorporates 'focused thrust' as explained in the recent Apogee 'Peak of Flight' newsletter:
https://www.apogeerockets.com/education/downloads/Newsletter363.pdf
That article well explains the reasons for using angled motors, plus an in depth instruction on laying out the dimensions of centering rings for this purpose. While I'd certainly agree that it is useful to know how to lay them out this way (for post-apocalyptic modeling, got my slide rule and dial calipers ready), I think you'll find that the small effort in reading and understanding the following OpenSCAD file will be well worth it.
The attached file "FocusThrustCRs.scad" is just a text file; you can open it with any editor and take a look. It's extensively commented, and you can probably get the idea by just taking a look at it.
To open it as a CAD file, requires the installation of OpenSCAD, which is available here: https://www.openscad.org/index.html It's available for Win/Mac/Lin, and installs very easily. Documentation and tutorials are also available at that site.
Here are some snapshots of what you can get from that file. All of the parameters are easily adjustable to get whatever result you want. All you're doing is placing two flat disks, then placing and subtracting the motor tubes from those disks.
You'll find that OpenSCAD includes a rudimentary text editor that does the job (or you can use your favorite external editor if you want). After changing anything in the file, pressing F5, will recompile the image (Menu Design/Compile). When you have something you want, pressing F6 does a compile and render (Menu Design/Compile and Render (CGAL)); and from there you can do a Menu File/Export/Export as STL... An .STL file is a common format used by all 3D printers, and should be usable by CNC routers as well.
Once you're bending things with CAD, you'll find that centering rings don't have to be a flat bit of cardboard or ply anymore. This example adds a shoulder around the center tube to keep the ring perpendicular, pockets out most of the ring for weight savings, adds ribs for additional strength, fillets everything to avoid stress points, and serrates the outer and inner edges to aid gluing.
Have fun.
View attachment FocusThrustCRs.txt
Ah, I notice that RO doesn't allow files with obscure extensions. After downloading the file, change the extension to .scad so that OpenSCAD can find and read it.
Gary
Last edited: