Duplo cannon

[Peter Blomberg]

The Duplo cannons are composed of multiple physical pieces screwed together. Looking specifically on the cannon with locking ring and red button 17178c01 or 94886c01.

What is the minimum that need to be modeled?

Some motors, projectile launchers, and springs have been modeled down to each screw and separable part even if that has meant the creation of (sub)parts with u numbers. Obtaining subpart numbers and internal structure requires opening the assembly, possibly destroying its play-ability in the process.

Rubber insets are sometimes modeled only by their visible parts.

Can the firing button be modeled as a red surface or does it need to be a separate subpart?

How accurately does the internal structure (metal spring and projectile guides) need to be modeled?

Do the screws need to be modeled as separate parts?

[Magnus Forsberg]

You are free to create and assume an inside structure, but each part has to be a closed 3D mesh. Use u-numbers.
The red button has to have some sort of structure, even if it is completely assumed. Simplify as mush as possible.
This "part" has to be a Shortcut, made of Parts. No Subpart is allowed to be in a Shortcut.

Since we know the correct assy number it might be possible to find the sub-part numbers without destroying the assy.
Do you want us to look for the numbers?

I don't have the part, but I assume one could look into the slot for the projectile?
Create something behind the slot to make it impossible to peek inside.

Have a look in the library for screws. Maybe there is a suitable screwhead on one of them. 
Ignore the length of the screw.