Original Design / Scratch Built
Contributed by Eldred Pickett
You can either purchase 4" rings and sand them down (much work) or find a place to get custom rings made. But once you get the rings, build your MMT normally, install an eye bolt for recovery, and install them in the crayon. 38mm motors work well with this project, although you can fit up to a 75mm motor in the tube.** You will also need to make a custom bulkhead to install in the nose cone.
If you use just one crayon, you'll have to add some nose weight to keep is stable. You can take measurements and run them through your favorite rocket design program to see exactly what you need. One thing to remember when doing the simulations is that the nose cone isn't exactly aerodynamic. It's flat on the top(like a crayon). So it won't go as high as it would with a smoother NC. But these creations are usually for show and not for performance.
You can also decide to use two crayons to build a longer or dual-deploy rocket. If you choose this, you'll need to make your own coupler. Recall that the crayon tube is smaller than a standard 4" tube. The Apogee Components website has an excellent tutorial on building custom couplers.
When you bring your new crayon to the launch field, be prepared for a lot of curious looks from spectators and other fliers. Enjoy!
** - I haven't flown a 75mm motor on a crayon rocket yet, so I can't guarantee that it won't shred. But I have flown 38mm and 54mm rockets with no problem. These tubes aren't as robust as a LOC or PML tube would be, but since you can build a fun high power rocket for less than $25 (including CRs), it's still worthwhile.
What You Can Do