Perry Mick wrote:

OK, I think I got it. Let me know if you see any problems. I will
replace the upper 1/8 x 1 x 1 aluminum extrusions with square steel
tubing with an endplate welded on and a hole drilled in the center for a
bolt.

Perry

Yep. That looks like it. Have your son make a 1/4 scale  balsa model to verify.

Paul Lamar

Ops just saw a problem. Can of worms. The model would show this quick.

Here is a simpler fix. Rubber rod ends. Still the one! :)

Paul Lamar

OK, I fixed it. Certainly looks bulletproof.
Perry

Ops again.

By fix it I hope you don't mean this.
This is still not fixed. If you build a model and twist it
you will see what flexes. This becomes a larger and larger
can of worm. A real bird cage Mass of Rattles (Masarati) limiting
access to parts.

BTW 3/16" square balsa wood has ideal characteristic for modeling motor
mounts as it has low modules of elasticity in bending while still maintaining
high compressive and tensile strength.

The strut with rubber rod ends solves a myriad of problems.
Also allows you to adjust the down thrust angle for max efficiency.

I hope you mean strut with rubber rod ends and not this one.

Paul Lamar

If you still want to use the third Barry rubber bushing as a front mount
this might work.

Decouple the front mount beam from the rest of the structure using rod ends
or rubber bushings. As Vance is fond of quoting some English engineer: "an
ounce of rubber is worth a pound of engineering." :) Sometimes you can add
too many tubes to a space frame and wind up with undesirable side effects
such as local bending moments in joints that lead to cracks.

Again 1/4 scale balsa stick models made from 3/16th square do wonders when
it comes to understanding a particular space frame design and I highly recommend
doing one.

Paul Lamar

I don't think I received your original email on this, and you didn't
include my corrected drawing in my original email. Here is my corrected
drawing again, see if there are any errors. I added the three tubes you
had redlined in.

Perry

Needs yet more tubes.

Paul Lamar
 
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