Even with long-exposure modified webcams where many medium length exposures (~1 minute) are used, we cannot tolerate drift, since the field of view is very narrow. Any drift will reduce the common field of view between captured frames, effectively prohibiting image stacking.
Accurate tracking is also important for very long focal length webcam imaging of the planets, as the field of view is extremely narrow. With drift, a planet will quickly disappear from the field of view.
Accurate_worm_period = sidereal_day_length / #of teeth = 86164 sec/144 = 598.3611 sec
The correct motor speed can be calculated from the transmission ratio between motor axis and worm axis. For the Vixen MT-1 motor, this is 1:1 but for the Sanyo Denki motors used in the Astromeccanica AM-V belt & pulleys configuration, the ratio is 4:1. A picture of the different motor setups can be seen below
|Vixen Super Polaris mount|
|Motor controller|| Vixen
|Stepper Motor||Vixen MT-1||Sanyo Denki
|# of motors controlled||1||2||2|
|PC remote control option||no||yes||yes|
|Power transfer by||spur gear||belt & pulley||belt & pulley|
|Correct Motor period||598.3611 s||149.5903 s||149.5903 s|
see also this page
|Time measured||3 hours||3 hours||1 hour|
|Measured (averaged) |
|598.3006 s||149.6018 s||149.9033 s|
|Measurement raw data||Image||MS Excel file||Image|
|0.010 %||0.007 %||0.209 %|
|Comment||Simple, good quality||Initial impression is very good.|| Tracking error >25 times larger than for MTS-3SDI .
The price is about the same as for MTS-3SDI.
Consequence of poor tracking for Astromeccanica controller: If a webcam imaging session started with a star at the center of the field of view, the star will have drifted off the webcam chip after 1hour 37min. In this situation, there will be insufficient overlap between webcam frames much earlier than that, so the estimated longest usable imaging session would be no more than 30minutes. I.e. this means you cannot leave the scope alone for more than maximum 30 minutes while imaging if no guiding is used. For SD-1 this value is ~10 hours, and for the MTS-3SDI it is even longer (i.e. long enough for the Sun to come up!).