When designing this rocket, the question of motor mount selection came up. Did we want to go with a 29mm motor mount or a 3 x 24mm cluster setup? My son had the perfect answer : "Both". This gave birth to the idea of using a interchangable motor mount configuration. This would allow for 29mm, various cluster combination, and even single 24mm motor flights. The optional payload bay (not shown in the picture) makes the Maxtermind quite tall which makes it more suitable than the short version for certain motors or motor delay choices.

Rocksim Files : maxtermind.rkt - maxtermind_short.rkt

The first Rocksim file shows the rocket with the optional payload bay. The second has the shorter configuration, as shown in the picture above.

Both files have the rocket in 3x24mm cluster configuration. While you obviously wouldn't want to do this with the real rocket, you can simply insert one motor (or more) for simulation purposes.

Be sure to adjust the "Mass Override" values to reflect your rocket's actual weight and center of gravity.

Parts list

In addition to the parts listed here, you'll need some basic rocketry hobby supplies. You'll need tools to cut the fins and adhesive. Wood glue can be used, epoxy can be used to form fin fillets. A ruler and pencil will come in handy too.

- 2 BT-80 body tubes (each 18" long)
- BT-80 nose cone
- BT-80 baffle kit
- Kevlar and elastic shock cord
- snap swivel (#1 size)
- 1/8" plywood fin stock
- BT-70 body tube (4 1/2")
- 2 BT-80 to BT-70 centering rings
- BT-70 coupler (1 3/4" long)
- 2 launch lugs (1" each)
- 2 balsa standoffs (1" long, 1/4" x 1/8")

If you wish to build the optional payload bay, you'll need these model rocket parts too :

- BT-80 body tube (18" long)
- BT-80 coupler
- coupler bulkhead
- small eye-bolt

The Maxtermind model rocket is probably about a skill level 3 project. You should be able to cut fins from plywood. You can use anything from a hobby knife (horribly slow) to a Dremel tool with diamond tipped cutting wheel (quick and easy).

Mark one of the BT-80 body tubes as "upper" and the other as "lower".

Swapable Motor Mount

Take the BT-70 tube and cut it down to size, if needed. It should be 4 1/2" long. Mark the tube at 1/2" from both ends. Glue the two BT-80 to BT-70 centering rings on these marks. This assembly is your motor mount. Glue it into the lower BT-80 body tube, the aft centering ring should be flush with the body tube.

Cutting and attaching fins

Start by printing the fin template. Cut it out and attach it to the fin stock with some masking tape.

Draw the fin template onto the fin stock with a pencil. After removing the masking tape, you'll have some gaps in your lines (where the masking tape was). Complete the lines with a ruler.

Cut out the fin and repeat this for each set of fins, for a total of eight (8) fins. Sand the fins to remove any imperfections from cutting, resulting in two sets of four matching fins.

Next, mark the lower body tube for fin and launch lug placement. Use the body marking guide for fin and launch lug locations. Draw circles around the body tube at 1" and 5 1/2" from the aft end of the lower body tube.

Attach the four aft fins to the rocket's airframe (lower body tube). Your model should look slightly different as the BT-70 motor mount should stick out the back. I simply hadn't inserted it yet.

Next, glue the forward fins on to the model rocket. Make sure they line up with the aft fins.

Shock cord and baffle

Tie a snap swivel to the exposed end of the Kevlar shock cord. Place a drop of white glue on the knot, to keep it secure. Next, tie a loop into the shock cord, about 12 inches from the end with the snap swivel. You can put a drop of white glue on the knot for the loop also. Tie the other end of the Kevlar shock cord to the elastic shock cord. Next, tie the other piece of Kevlar to the remaining end of the elastic shock cord. This end of the Kevlar is attached to the baffle kit.

The snap swivel is attached the the eye on the nose cone. I have seen cases where a snap swivel got bent out of shape. If you wish, you can make a loop in the Kevlar were you would attach the snap swivel. Then use a small quicklink to connect that loop to the nose cone.

The baffle kit is used as a coupler. Build the baffle according the instructions that come with it and attach the shock cord as indicated earlier. The baffle shown here is a Sunward BT-80 baffle kit. Put glue inside the forward end of the lower body tube. Insert the coupler half way. Let the glue dry. Next, put glue inside the aft end of the upper body tube. Slide the exposed end of the coupler into the upper body tube. This joins the two body tubes. Set aside to dry.

Launch Lugs

Cut two pieces of 1/4" launch lug, each 1" long. Also cut two pieces of balsa strip (1/4" x 1/8", each piece 1" long). These will be used as standoffs.

Glue the launch lugs onto the standoffs. This will help protect the paint job when flying this model rocket.

Optional super-sized payload bay

As you can see in the photo, an eye-bolt was epoxied to a BT-80 coupler bulkhead. This ends up being on the heavy side, lighter materials may be more suitable.

Glue the bulkhead into the coupler and let dry. Measure the lenght of the coupler. Put it half-way into a body tube and draw a line around the coupler.

Place glue inside the bottom end of the payload body tube and insert the coupler until the line is flush with the body tube. Let the glue dry.

Measurements

The Maxtermind is BT-80 based and has a 2.6" airframe diameter with a 8.6" fin span. Without the payload bay, the rocket is 46" long and 63" with optional payload bay.

Finishing

Obviously, you can paint this flying model rocket any way you wish. To match the paint job in the picture shown at the top of this page, continue reading... First, the entire rocket (including nose cone) was painted yellow. After 24 hours, everything but the forward fins was masked off. The forward fins were painted red. Another 24 hours later, the whole rocket expect the aft fins was masked off. The aft fin set was painted orange. For some detailing, the entire rocket was masked off, expect for the top 1/4". This top section was painted red. The optional payload bay was also painted yellow. The top 1/4" was also painted red.

Flight Data

The weight of the rocket will depend on construction. As such, each rocket will behave differently on different motors. I suggest using Rocksim (with "mass override") to determine which motors have suitable delays and to ensure the model is stabel.

To fly it on a cluster of 3E's, a heavier (1.5oz) beeper was attached to the nose cone, just to make sure it was nice and stable (and to help find it). Never fly a rocket unless you are sure it is stable and safe to fly.

Video : Cluster of 3 x E9-6 Single G64 Another 3 x E9 Flight G33 Drag Race F24 RMS reload