Best crack repair without shell exchange?

[Bad Andy]

Thus the Superglue + Baking Soda fix.

Sorry to seem obnoxious but it's gonna take more than relative strength of wood finishing lacquer to convince me that baking soda tangibly benefits the shear strength of CA. Though if the surfaces aren't well-matched I'm sure it does help.

Anyway, nobody knows the type of plastic used for these shells??

 

[Brojon]

Sorry to seem obnoxious but it's gonna take more than relative strength of wood finishing lacquer to convince me that baking soda tangibly benefits the shear strength of CA. Though if the surfaces aren't well-matched I'm sure it does help.

Anyway, nobody knows the type of plastic used for these shells??

You did notice the link to a scholarly research paper - right?
Or you just that eager to poo-poo something you don't know?

 

[Bad Andy]

You did notice the link to a scholarly research paper - right?
Or you just that eager to poo-poo something you don't know?

Honestly, after seeing "the strength of the material normal to the layer plane is significantly lower than that parallel to the layer plane", I decided to skip reading the paper.

It is notable that voids in the bond (which baking soda would at least partially address) were correlated with early failures.

The rest of the paper at least in a brief scan does not seem to contradict me, and does confirm anisotropy.

Oh, it should be noted for the benefit of readers here that CA adhesives rely greatly on good compression between surfaces. Shell disassembly before use is probably wise as a result.

I still think folks would be better off using products made specifically for the type of plastic in use. And I can't believe that with the breadth of in-depth knowledge in this community, I can't seem to find anyone who has been able to say anything more definitive than "plastic".

 

[Brojon]

Most adhesives do have less strength in lateral shear. Heck most materials in fact are more prone to fail with shear forces - nothing new there.
Easier to break a stick by bending than pulling it apart. Perfectly normal for the most part.
I don't think any plastic repair product results in a stronger join than the original - not even ultrasonic welding can make that claim.
It's not even obvious that the shell cracks result from any kind of shear.
The advantage of CA and baking soda over a glue is that it will address voids, bridge gaps and is rigid when it cures - unlike plastic glues which depend on some degree of solvent action to create the bond.
So I'm not sure why the critique when shear strength may not even be applicable and a repair is certainly preferable to a fractured part.

 

[Bad Andy]

Most adhesives do have less strength in lateral shear. Heck most materials in fact are more prone to fail with shear forces - nothing new there.
Easier to break a stick by bending than pulling it apart. Perfectly normal for the most part.
I don't think any plastic repair product results in a stronger join than the original - not even ultrasonic welding can make that claim.
It's not even obvious that the shell cracks result from any kind of shear.
The advantage of CA and baking soda over a glue is that it will address voids, bridge gaps and is rigid when it cures - unlike plastic glues which depend on some degree of solvent action to create the bond.
So I'm not sure why the critique when shear strength may not even be applicable and a repair is certainly preferable to a fractured part.

I've had impressive results from solvent products.

YMMV! ;-)

The cracks are from what forces? Torque? I can't imagine tensile.

 

[Brojon]

That's an excellent question that also has no apparent answers.
Most folks assert they haven't crashed the bird. The motors are isolated from the shell near as I can tell from disassembly videos.
Why on the top half?
I honestly don't know what forces are acting on the shell to cause the cracks, but I doubt it's torque. Most cracks I've seen photos of track the curvature of the "well" that cups the motor and go back down the arm. This would incline me to believe these are internal stress points from the molding process. I wonder if the shells are stamped using sheets of plastic and heated dies.

 

[Bad Andy]

The upper half of the shell would be seeing compression forces, no?

EDIT: Wait, small amounts of torque also, since the motors are cambered?

 

[RémyHeli]

Crack might not necessary happen while flying but knock on the arm etc., similar to Helihover (#18).

 

[RémyHeli]

This would incline me to believe these are internal stress points from the molding process.

And possibly weak points such as tighten motor screws and their hole as crack starting point.