Thought I would pass along some info to those building or considering any of the Roban 700-800 series helis with elevated tail rotors. This applies to the assembly of the main torque tube, angled gearbox, short torque tube & short torque shaft, and 90degree tail rotor gear assembly. Hopefully, this info will eliminate bevel gear shearing in the angled gearbox.
Roban engineers their tail drive components for easy & accurate assembly by providing pre-drilled holes & corresponding molded locator tabs in critical areas. Assuming the builder is diligent in sliding both the long & short torque tubes into the correct locator tab position in the angled gearbox, it all assembles very straightforward. If your tail rotor rotates silky smooth, with no rough spots or “grabbing” at all, read no further. My AH-1W Cobra was perfect. My B412 Canadian Rescue tail rotor blade would rotate one gear tooth at a time, then stop. If I tried to spin it by hand, the tube vibration was obvious.
It took awhile to figure out the problem was a misalignment of the short torque shaft between the 90 degree bevel gears & the angled gearbox. I had mounted the 90 degree tail rotor gearbox to the short torque tube previously as that is required to mount the mechanics in the fuselage. So, as a last resort before cutting brass shim stock, I removed the side “fixing screw” on the 90 degree gearbox’s short torque tube locator hole & all the rotational binding disappeared. I snugged everything back up & it’s still good. I verified this screw is not touching the short torque shaft, so I assume installing the 90 degree gearbox without the short torque shaft present allowed the assembly to cant off center slightly.
Moral to my story is make sure to install the 90 degree gearbox on the short torque shaft & tube last, then when the 3 screws are tightened it will stay aligned when you remove the short tube assembly later for fuselage assembly.
Roban engineers their tail drive components for easy & accurate assembly by providing pre-drilled holes & corresponding molded locator tabs in critical areas. Assuming the builder is diligent in sliding both the long & short torque tubes into the correct locator tab position in the angled gearbox, it all assembles very straightforward. If your tail rotor rotates silky smooth, with no rough spots or “grabbing” at all, read no further. My AH-1W Cobra was perfect. My B412 Canadian Rescue tail rotor blade would rotate one gear tooth at a time, then stop. If I tried to spin it by hand, the tube vibration was obvious.
It took awhile to figure out the problem was a misalignment of the short torque shaft between the 90 degree bevel gears & the angled gearbox. I had mounted the 90 degree tail rotor gearbox to the short torque tube previously as that is required to mount the mechanics in the fuselage. So, as a last resort before cutting brass shim stock, I removed the side “fixing screw” on the 90 degree gearbox’s short torque tube locator hole & all the rotational binding disappeared. I snugged everything back up & it’s still good. I verified this screw is not touching the short torque shaft, so I assume installing the 90 degree gearbox without the short torque shaft present allowed the assembly to cant off center slightly.
Moral to my story is make sure to install the 90 degree gearbox on the short torque shaft & tube last, then when the 3 screws are tightened it will stay aligned when you remove the short tube assembly later for fuselage assembly.
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