I checked briefly and previously the balance of both motors concerning their revolutions in the manners as seen in the pics below at a piece of 1.3V Nimh battery. The test was done to know how many rotation may be the starting point, by which I could know the smoothness or silence of the motors mainly. In other words, the rotations will be so-called "idling status" for these motors.
Moreover, I could confirm how smooth and well the connections among the motors, couplings and screw shafts were at a higher
voltages.
The result was...so silent, so smooth and so slow enough to be able to see the coupling as its original still shape while
rotating in around 1900 RPM.
![Thumbs up :-))](http://www.modelboatmayhem.co.uk/forum/Smileys/Tug/thumbup.gif)
I regarded these setups as serviceable for a RC boat to operate on our lake,
where noisy RC boats have been strictly prohibited to sail for many years.
Needless to say, both stern tubes were filled with grease completely and the 1900-2000RPM idling was achieved at 1.3V.
This MTB has run well later on subsequently as seen in my previous video.
![OK O0](http://www.modelboatmayhem.co.uk/forum/Smileys/Tug/smiley.gif)
1900 and 2000RPM were acceptable to me in balance test and subsequent performance of maneuverabilities on the water.
1;stern tubes were filled with grease and tachometer was set. Let's go the test....expecting a stable rotation...
2;Left motor ..1900RPM rotating stably enabling the coupling in nearly in its still mode at 1.3 V battery.
3;Right 2000RPM
The motors were getting a bit warmer in several minutes test like high and low speed and then finished.