I am considering designing an equatorial mount for astrophotography. I have been researching on the best way to do that and I am thinking on using a stepper motor with a gearbox. The thing is that it needs to turn at a really low speed, 1 rev/day. If I pick any Nema X motor I can get it to step 200/400 steps without a gearbox. The most reductions I have found are 1:100 (this is an example: http://www.ebay.com/itm/Nema17-23-34-Planetary-Gear-Ratio-5-1-10-1-15-1-20-1-30-1-40-1-50-1-100-1-Reduce-/201844830182?var=&hash=item2efee3afe6:m:mPuljSiQP2wMMZ69Cmf4BYA)
That means that I can get 20.000 steps/rev (400 step/rev motor) which would mean running the motor at 20.000/60*24 = 14 steps/min --> 4.34 sec/ step. I don't think the operation is smooth enough so it will might show in the pictures.
I have been researching on other similar projects and I have seen that they picked 1rpm as acceptable for that smoothness (0.15sec/ step for a 400 step motor). That means that I need a gearbox capable of around 1500:1. My questions is as follows: - Does it make sense to add 2-3 gearboxes in series to get that value? Like those ones and adaptors for the output shafts since they are different in size to the input shafts: http://www.ebay.com/itm/NEMA34-NEMA23-Stepper-Motor-Planetary-Gearbox-36-1-30-1-24-1-16-1-10-1-6-1-4-1/122395466919?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D44757%26meid%3D57a6af176f9b48e0b9f2042efc480bc1%26pid%3D100005%26rk%3D3%26rkt%3D6%26sd%3D122395466919&var=422871734736. An example could be adding first 30:1, second 30:1, 2:1 (1800:1 all together).
- Would it be better to design a planetary/spur gearbox to satisfy those requirements?
Thank you. I hope this is the right forum. I haven't find one suitable for mechanics