Any backyard astronomers here, who could shed some light? - Page 1
Forum section: electronics / projects

author: miceuz
author_rank: Frequent Contributor
timestamp: December 13, 2013, 04:03:51 pm
content: I got a telescope with the whole mount and an equatorial tracking stepper motor. Looks like it's EQ-2 motor. I'm going to give the telescope as a Christmas present to a kid from poor family and I want to build a driver for this motor, so the set is complete.The problem is I know zip about astronomical gear. While building a stepper driver is no big deal for me, I still don't know how fast the motor has to rotate - i.e. what frequency and width of the pulses have to be so that the telescope compensates for the Earth rotation correctly.I thought, maybe someone here has an EQ-2 set and can measure some waveforms for me? Or provide any kind of information for that matter?

author: bitelf
author_rank: Newbie
timestamp: December 13, 2013, 04:31:55 pm
content: If you have a small, battery driven EQ-2 box attached to your mount it is an equatorial clock drive and not a stepper drive. It allows the scope to follow an object at a single constant speed as the Earth's sidereal motion is fairly constant.http://en.wikipedia.org/wiki/Equatorial_mountHere is a good read on a DIY drive system and software:http://www.bbastrodesigns.com/BBAstroDesigns.html#Computer_Operated_TelescopesAfter reading this you may conclude that the ~$79 cost of a commercial drive system isn't too bad.

author: hgg
author_rank: Frequent Contributor
timestamp: December 14, 2013, 08:36:01 am
content: Hi,You have to know your gear ratios and drive the motor in order to achieve a Sidereal tracking rate whichis the rate at which the stars appear to move in the sky. Basically your motor should makethe right ascension RA axis of your mount turn a full 360deg rotation in 23.93447 hours.I assume that the motor is attached to the mount and it only needs a driver.You have to disassemble the RA drive and count the teeth of the worm gear.In the case of the EQ-2 I think is 144 teeth. You need this for your calculations.Maybe you'd be better off with the following:http://www.ebay.com/itm/RA-Telescope-Motor-Drive-Hand-Controller-M4-for-Seben-EQ3-EQ2-mount-/380420218709?pt=AU_Cameras_Telescopes_Binoculars&hash=item5892cfdf55orhttp://www.optcorp.com/open-box-orion-eq-2m-electronic-telescope-drive-7827-7050.htmlbut if your finally decide to do it, please post the final motor driver because I also have an oldmount that I would like to revive...

author: miceuz
author_rank: Frequent Contributor
timestamp: December 15, 2013, 08:06:18 pm
content: I agree, that the task is more complicated than it might seem, but I have a limitation that prohibits me from purchasing a ready made drive - I have to have the thing till Christmass.The motor I have looks exactly like this:Well, I just went and built a simple stepper driver out of parts from my junk bin:Essentially it's just a replica of a chinese knock-off of I don't know whatThe only addition I've made is a potentiometer that allows to fine tune the rotation speed.I'm planning to run it on 4 D-cells tapping 4.5V after 3 cells for MCU.I've had some help from this guy - he had some ideas about the speed of the stepper needed:http://astrobling.weebly.com/drive-motor-speed-adjuster.htmlIf anyone is interested, schematics and source code is here:https://github.com/Miceuz/astromotor

author: westfw
author_rank: Super Contributor
timestamp: December 15, 2013, 11:54:41 pm
content: QuoteIt counteracts the earth's rotation, so it needs to rotate one rotation per day."Exactly" will let you do things like do long-exposure photographs and separate the stars from the other stuff (assuming you've oriented the scope exactly correctly.) But "close" will keep the relevant objects from drifting out of view while you call you siblings/etc over to come look. (Otherwise, things remain in view for about 1 minute on a typical telescope?)If it's actually a stepper motor,, then aside from gear ratio, the big question is probably whether it "needs" microstepping (also dependent on gear ratio, I guess.)

author: Lightages
author_rank: Unknown
timestamp: December 16, 2013, 12:28:24 am
content: A telescope needs to rotate once every 23 hours, 56 minutes, 4.1 seconds, more or less. This is equal to 15.04° per hour. This is known as the sidereal day which is the time it takes the earth to rotate once relative to the stars. To follow the moon exactly you need another speed which is called the lunar rate, or about 0.5° per hour less. This is not an exact number as the moon gets closer and farther away from the earth its orbit it speeds up and slows down.

author: ahnuts72
author_rank: Regular Contributor
timestamp: December 16, 2013, 09:09:27 am
content: Need to remember all this becomes a moot point if the polar alignment is not close to right.The further off your alignment the faster an object will leave the field of view.

author: Kremmen
author_rank: Super Contributor
timestamp: December 16, 2013, 12:43:37 pm
content: Quote from: ahnuts72 on December 16, 2013, 09:09:27 amA good point and many "serious" mounts include a hollow tube for the RA or hour axis, enabling installation of a small pole finder telescope that has the location of Polaris and other direction finding info engraved permanently in the field of view. Alternatively such scope can be mounted somewhere else in the fixed structure of the mount.