The 'hi-motor' Beaver variant can take a standard motor fitting, but there is very little room under the prop shaft for the lo-motor. Design space is about 1 inch total - so we need no wasted space with a mount lifting the motor up. I used a simple made-up mount as below:
So long as the motor is small, without a high starting torque, the spring steel will hold it quite firmly.
Install a thin balsa mount parallel to the prop-shaft, and drill a couple of holes in the mount base to help the glue hold strongly...
Use an epoxy to hold the base to the balsa plate, checking that the assembly remains parallel to the prop-shaft...
...and confirm that the pulley is going to sit square with the prop-shaft pulley, and with adequate clearance.
Here is a bit of thin sheet steel - an old floppy drive cover, actually. Anything fairy springy will do.
Cut
two strips, bend one around the motor body and solder it onto the other strip. Pretty simple! And it only adds 0.05" to the height...
There it is, tucked away, yet easy to slide out for replacement...
