Rubicon Motor Retention and Nose Weight

For motor retention, a simple and lightweight option was to epoxy some 2-56 threaded rods into 3 places at the back of the rocket. It only takes a nut and washer on each of these to keep all 7 motors from sliding out backwards.

Some aluminum carrier tubes and the threaded rods.

Epoxied in place on the central motor tube.

Ready to epoxy to the rest of the airframe.

Showing my Pro 24 motor case installed and held in with the washers.

Since I am going to be using 7 motors, I have to be able to balance that weight out to make the rocket stable. Unfortunately, this means adding a lot of weight because it is a short rocket. It looks like I will have to use around 16 ounces of nose weight with 7 motors installed. 

I constructed a 24mm tube with a 5/16" threaded rod down the core and epoxied it in place into the nose cone. This way I can add 5/16" washers until the proper balance is achieved and simply thread on a nut to hold the washers in place. It's basically a simpler version of the nose weight system in Positive Ascent.

Pouring the epoxy into the nose cone to hold the assembly.

Estes Rubicon

I bought a discontinued Estes rocket called the Rubicon. It is designed for use with a single D12-3 for altitudes of about 400 feet. Since there are 7 24mm tubes making the majority of the rocket, it was a simple decision for me to make all 7 of these tubes into motor mounts. The project itself is no where near as simple, but rather a fun and challenging project.

Instead of simply clustering all 7 motors and lighting them on the ground, I am going to light some on the ground and airstart others with my Perfectflite Mini Timer. I also decided to make the rocket carry my Perfectflite altimeter for dual deployment, and since I will be able to get altitudes in excess of 4000 feet, I also made it a goal to carry my tracking transmitter so I don't lose it as easily.

The main components set together

The plastic fin can. 

I had to do some Dremel work to clear out the aft bulkplate that was molded into this piece.

The plastic forward bulk head.

The red tube carries the wires from the timer to the back of the rocket for the igniters for the airstarts. The hole into one of the booster tubes is for clearance for the altimeter.

I made 2 new 1/16" ply centering rings to make the whole structure stronger. All the electronics must fit between the plastic bulkhead and the wood centering ring seen here.

The 2 wood centering rings. There are 4 2-56 blind nuts to be used in joining the main tube to the rest of the rocket in an easily removable way.

Here's the side with the timer and the on/off switches. The upper centering ring will be glued inside the main body tube and the 4 2-56 screws will hold the assembly to the lower centering ring.