[JVN]

It is exciting to see someone post something that looks like it could actually be built.
Excellent job Arefin, you've come a loooong way!
It is apparent you've put some serious time in on this design.

Of course... now you know my advice for the next step.
Keep tweaking/tuning!

The shifter may need a little bit more work. As others have said, you may be able to get some more weight out of it; but making up a quick lightening pattern for a gear is something that can be done later.

Props, for making both gearbox plates identical (and also for accomplishing the entire design with only 3 different gear sizes!). Two plates, 2 shafts... simple and elegant. It shows you've put some thought into the design. (As opposed to some transmissions, which contain 20 different plates, some of which cannot be made outside of the magical world of "inventor").

If you tell me you've got a print-package made up, I may just wet myself.

Kudos,
Can't wait to see the next revision. (No, you're not done yet. You still have 4 months.)
-John