Thank you for your feedback, we received some reports from users that the CAA device exhibits a certain amount of backlash, meaning there is slight movement at the output end of the CAA when a torque is applied to the rear load of the CAA. Your feedback is very important to us, and we’d like to address some questions we’ve received and clarify what might cause this and what steps we’re taking to ensure product consistency and quality.
The backlash phenomenon only has an actual impact on the performance of the CAA when eccentric torque changes. That is to say, under normal operating conditions, as long as the center of gravity position of the optical devices (such as filter wheels, cameras, etc.) connected to the rear does not change, thus not causing a change in eccentric torque, even if there is backlash present, it will not substantially affect the operation of the rotator. Only when the position or mass distribution of the equipment attached to the rotator changes (such as before and after meridian flip), leading to an eccentric torque exceeding the threshold that can be compensated by the internal mechanism of the CAA, might the backlash become apparent and possibly affect the accuracy and response speed of the CAA. Therefore, if users are still concerned about the backlash of the CAA, they can consider adding a balancing module to the rear load of the CAA. Keeping the balance and stability of the center of gravity of the optical equipment is crucial, which can minimize the impact of backlash on the results of astrophotography.
Theoretically, to ensure that the target displacement of the farthest pixel position on the sensor of a full-frame camera (taking ASI6200 as an example) does not exceed 1 pixel, the backlash at the motor output end should be controlled within no more than 0.01°; if the maximum allowable deviation is 10 pixels, then the backlash limit can be relaxed to 0.1°.
After testing and full inspection by ZWO, the backlash of all CAA units upon factory release is controlled within 0.3°. For deep-sky photography composition and mosaic requirements, this level of backlash generally does not significantly affect user experience because, in most cases, the precision required for the use of camera angles is 0.1°, and the angular resolution accuracy of the image is approximately <0.5°. Considering all three factors simultaneously, the overlap rate of different images stacked due to minor rotation of the camera image still exceeds 97.8%, sufficient to meet regular needs.
In summary, although there is a certain amount of backlash in the CAA hardware, as long as the backlash is controlled within a certain range, it will not cause obvious negative effects on the final imaging quality. For applications requiring higher precision control, the influence of backlash can be minimized by adding a balancing module to the load.
