Design and construction update. Over the last year I've taken a NoseCam above Mach on three different occasions. In all cases the brushless gimbal motor that rotates the nose shell would stall at or just above Mach, and then recover once the rocket slowed enough. I had already doubled the torque of the motor by increasing the motor voltage rail to 32V, but that didn't solve the problem, although it did move the stalling to higher velocities.
I've never been thrilled with relying on the internal bearings of the gimbal motor to act as the load bearing axis of rotation for the entire upper nose. These motors were never intended for this type and magnitude of loading. I'm happy that the gimbal motor bearings work as well as they do as long as you stay below Mach. I don't think that overloading the motor bearing was the primary cause of the motor stalling (more on that later), but I felt it was time to give the motor bearing a little help carrying the aerodynamic and inertial loads.
I modified one of the stationary lower shell pieces so I could install six miniature ball bearings with 2mm stainless dowel pin axels. The outer perimeter of the rotating nose shell support now presses against these bearings, taking some of the thrust and bending loads off of the gimbal motor bearings.
As to the primary reason for motor stalling, I have a pet theory. All versions of NoseCams (up until now) have had a thin sleeve of plastic at the bottom of the rotating nose that overlapped the stationary motor housing. This was done primarily for looks, since it hid a bunch of hardware gaps. I'm guessing that at high velocities a venturi effect of airflow over the nose would pull a vacuum on the inside of the nose. The air pressure differential across the thin cylindrical sleeve of plastic would cause it to get pushed inward and drag on the stationary components, almost like a drum brake. It's my belief that this was the primary cause for the motor stalling. The modified nose design no longer has this thin sleeve of plastic. It doesn't look quite so nice anymore, but I hope all these fixes solve the motor stalling problem.
I've never been thrilled with relying on the internal bearings of the gimbal motor to act as the load bearing axis of rotation for the entire upper nose. These motors were never intended for this type and magnitude of loading. I'm happy that the gimbal motor bearings work as well as they do as long as you stay below Mach. I don't think that overloading the motor bearing was the primary cause of the motor stalling (more on that later), but I felt it was time to give the motor bearing a little help carrying the aerodynamic and inertial loads.
I modified one of the stationary lower shell pieces so I could install six miniature ball bearings with 2mm stainless dowel pin axels. The outer perimeter of the rotating nose shell support now presses against these bearings, taking some of the thrust and bending loads off of the gimbal motor bearings.
As to the primary reason for motor stalling, I have a pet theory. All versions of NoseCams (up until now) have had a thin sleeve of plastic at the bottom of the rotating nose that overlapped the stationary motor housing. This was done primarily for looks, since it hid a bunch of hardware gaps. I'm guessing that at high velocities a venturi effect of airflow over the nose would pull a vacuum on the inside of the nose. The air pressure differential across the thin cylindrical sleeve of plastic would cause it to get pushed inward and drag on the stationary components, almost like a drum brake. It's my belief that this was the primary cause for the motor stalling. The modified nose design no longer has this thin sleeve of plastic. It doesn't look quite so nice anymore, but I hope all these fixes solve the motor stalling problem.