|
After having success with my BT-60 Interchangeable Motor Mount System, I decided to do one for BT-70 tubes (2.175" inside diameter).
Building my second Thridget, this time a 2.6"
diameter (BT-80) upscale, I didn't want the 3x24mm motor mount to be
permanent; I wanted to be able to fly other motors in the rocket.
So it was a good fit for using an interchangeable motor mount system.
Left: This it the aft end of the 2.6" Midget with the 3x24mm mount
installed. The nut at top retains the mount in the rocket.
The one in the center is part of the mount and retains the motors (in
single stage applications; they must be friction fit in staged flights). |
In staged configuration, there is little indication that the motor mount is removable.
|
|
|
As with the BT-60 system,
a piece of all-thread runs from just aft of the opening forward to a
bulkhead which acts as a thrust ring for the motor mount as well as
being an anchor for the all-thread, and also for the shock cord leader
(on the forward side of the bulkhead).
|
So
far, I have built three rockets incorporating the system. In
addition to the Midget, two 2.34" diameter rockets incorporate
it. Since that size tube slip fits over BT-70, it was an easy
setup.
On the left is a rocket tentatively called the Raider which uses the Firefox 2.34" tube (RBT225). The Midget is in the center.
At right is the Hawks Hobby Cherokee 3D which uses Semroc's 2.34" tube (Series 225).
While the two tubes are or very different construction, they are dimensionally equal.
The six motor mounts shown in the pic can all be installed in any of the three rockets.
|
|
The motor mount units handle the following combinations of motors:
Left to right, top to bottom:
- 3x18mm + 4x13mm
- 2x24mm + 2x18mm
- 1x24mm
- 1x38mm
- 1x29mm
- 3x24mm
|
Frankly, I wonder if some of these will ever see actual use  But sometimes I get a get a little carried away 
So far, I've flown the 3x24mm once, in the Midget. And the 38mm unit
once, in the Cherokee 3D. I'm sure the 29mm adapter will see some
service, and maybe the 1x24, but the other two are iffy, especially the
one on top. It's more of a "something I can make" than a "something useful I should make" 
|
|
