astrotrac polar scope collimation

 Without any change to the polar scope, the error can be reduced to 8' to 10' ( 1/4 to 1/5 of 40 min polaris-NCP angular distance) . Some can achieve even smaller errors, YMMV. I am using TV aerial method

set the polar scope, so that one of grub screw is at 12 o'clock. only adjust the other 2 grub screw in each cycle
horizontal ( 3 o'clock , 6 o'clock) and then vertical direction( 12 o'clock and 6 o'clock).
turn the scope 120 degrees, so that the other grub screw is at 12 o'clock

repeat above steps as many as you can

Now change the grub screw with M3 x 10mm thumb screw, the error is reduced  4' to 5 '( 1/8 to 1/10 of 40  min polar-NCP angular distance

but still, when  you rotate the scope, the field is rotated together with the rotation.

So far the main drawbacks of existing design are:

Need to rotate the polar scope, which is held in place by 3 magnets.

The polar scope arm flexure. There is no way to keep the polar scope in tight parallel to the RA axis.

So hopefully, for the next version of astrotrac:

the polar scope arm is changed to fixed position type using some sort of screw lock, so that the arm cannot swing in or out. The polar scope is parallel to RA Axis by design

Discard use of the plastic tube for front objective. Change use of metal tube, and the threads are machine milled to keep tight tolerance.

Stop the need to rotate the polar scope, and same time the reticle is change to ioptron's polaris circle style.

use a higher magnification. Anyways, in city area, only the Polaris is visible, which the other 2 stars are too dim to be of any use

use thumb screw instead of grub screw to adjust the reticle

use a more durable illuminator. The  volume switch is easily damaged