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Nov 21, 2012, 04:39 AM
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The battle of the camera mount

So after all its calibration, the IMU on the camera mount was not accurate enough to improve camera pointing. Magnetic heading was always slightly off & required very precise calibration. It may have been magnetism from the servos. That led back to hacking into the servo pots.

The only way inside the winch servos was to desolder the motors. That revealed the pot was indeed exposed on the outside, but undetected due to a probing error. Those $50 winch servos have some beefy MOSFETs & a big motor. $50 buys a lot more than $10.

While staring at this $50 servo's crumbling lead free soldering with no conformal coating, it should be noted that it's no good for a mission critical aerospace application. The soldering is going to have tin whiskers.

The servos only use 1V of the full range of the pots. They leave a 1V buffer on each end. This seems to be because of the strange behavior of the pots. They don't have upper & lower stop points.

With no PWM, they can be manually spun beyond the maximum revolutions, using some kind of slip ring, then wherever they reverse direction becomes the new boundary. The servos have the 1V buffer to avoid changing their center points.

Of course, this means the center point changes depending on how the camera mount is rotated when it's off. The easiest solution is to put mechanical stoppers in the mount to stop it from rotating beyond the boundaries.
Last edited by Jack Crossfire; Nov 21, 2012 at 04:55 AM.
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