When performed first test run of AR2, suddenly J2 motor did not move and It appeared as the gear is disconnect with "crack crack" sound.
Below is the video link to show the problem where gear is not turn when motor is on.
https://drive.google.com/open?id=1j9uHmCQJbXa_a6Hua-s0aS3uwqeXK1NA
Spending couple of days via email with OMC technician to trouble shoot and root cause finding. The technician concluded that the M6x20 cap screw is causing gearbox deformation which might be irreversible. Below is the photo what OMC technician email me:-
https://drive.google.com/open?id=1JEy1Y1HE6WUywVh0ybPT5_8eqZEKMQWr
I decided to change the way J2 Nema23 motor screw on J2 Motor Support. Below is the photo example:-
https://drive.google.com/open?id=1wz636eNQobWJW6JIxhmENsC_CdGa6iAU
By using 4 M4 cap screw and washer between J2 Motor Support and J1 Platform.
AR2 has been running 6 hours (yesterday) and 4 hours (today, now still running) without J2 motor gearbox problem, I will update if problem keep come back which J2 motor gearbox deformation already irreversible and have to replace with new one.
M6X20 cap screw and locking might not needed in aluminium structure which original is for 3D printed.
After running AR2 for another 4 hours. The J2 motor gearbox problem does not not come back (touch wood). I did not use M6X20 cap screw at all. I will continue perform other test and hopefully this will not has any impact on AR2 when it is on production operation.
Thank you for the detailed feedback. I will add information to the manual to only tighten M6 screw enough to secure gear box radially but not overclamp or deforms planetary gear housing.