Equatorial Newtonians, 20" and 14" "The purpose of life is to be defeated by ever greater things." - Rielke
Quote:Anyone on here done it? I keep thinking how nice it would be to have Tracking on my GEM mount.
Quote: I haven't used steppers but I know they can be noisy and vibrate a lot.
16"F4.5 meade Starfinder Rebuilt into Truss Dob, with refigured primary. Equatorial Platform 8"F6 Homebuilt dob Orion 4.5" Starblast Meade ETX-60 www.mnastro.org
George You know you're getting on when the equipment you farmed with is showing up as suburban lawn ornaments.
Quote:Certainly, a drive based on your basic synchronous clock motor is the most straight forward approach. Not a lot of torque, but they are generally are at the end of a very high gear reduction ratio. For reasons never explained to me, my dad couldn't seem to pass up a bargain on clock motors. So I inherited quite a collection in various output ratios. So there are lots of gearing options. Celestron used a lot of 1 revolution per hour outputs to drive the original C8 spur gears. IIRC the output gear is 12 teeth (tooth?). So for a solar day of 1440 minutes and 12 teeth/hour we need 12 * 24 = 288 teeth on the main gear. Oddly, the RA/AZ gears used on the Nexstar goto mount also had 288 teeth. Meade used worm gears in most of their mount early mounts. A 180 tooth worm wheel was the most common. With a simple clock motor rotating the worm at 0.125 RPM or once per every 8 minutes (8 * 1800 = 1440) you get your solar day. The rarer 360 tooth wheel used a 4 rotation/minute worm. Celestron sold about 20,000 mounts with Byers worm gears including a few with clock motors. The Byers wheel had 359 teeth, which when driven by a 0.0625 (1/16th) RPM motor gets you a sidereal day (1436 minutes). I gave these worm gear sets available for sale.
Quote: The speed of synchronous motors can be controlled to a limited extent by changing the frequency of the AC line signal. Autoguiding is possible with the proper circuitry. See: code.google.com/p/ultima8drivecorrector/Stepper motors seem to come in and out of favor. It is no longer true that a stepper setup need be noisy of create vibration. The latest Synta EQ-6 uses steppers. Steppers came into favor for precise motion control earlier than servo motors as the electronics needed to control them were somewhat simpler. As processors got more powerful servo motors in closed loop control systems became the norm. Now with even more powerful processors steppers are getting a second look. Running microprocessors at higher frequencies permits finer micro-stepping that greatly smooths out a stepper. The PICgoto Yahoo group (Picgotogroup@yahoogroups.com) has several PIC microprocessor based stepper driver designs developed by members. The drivers are controlled by a WinPC with freeware from the group. The freeware has been ported to other platforms. The Roboscope Yahoo groups specializes in adapting the Meade Autostar goto system to other mounts. Autostar is a closed loop servo-motor system controlled by two or more networked microprocessors. It's great advantage is that it's fairly cheap and easy to adapt to other mounts.As may be gathered from the above some precision and control system is the norm for mount drives. Running a low voltage DC motor with a simple resistance control is not going to get you any precise speed. Speeds will vary a lot with changing loads, temperature, etc. Even simple voltage control systems like Meade's LX-10 and ETX90-RA aren't suitable for any extensive tracking. The Celestron Logic drive mentioned has a better system that may serve you needs. I've diagramed the circuit and built a working clone that I'm still experimenting with. To work with this you'll need a 6-24vDC motor with a reducing gear head. This one from Marlin P. Jones & Assoc. Inc. should work; http://www.mpja.com/03-05-13-B.asp?r=340400&s=39Here's a couple of drawing I made of the logic drive circuit. Upper is the original PCB the lower is my layout on Veroboard. I omitted the reversing and on-off switches. My layout measures about 1.5 by 1.25" when finished.
Scopes: Meade SN6, 10" Dob, Meade LS6, 5" reflector, 8" reflector, 102GT
Mounts: LXD75 and LXD55
Camera: SBIG 8300M, Baader 7nm Ha, OIII, SII, LRGB
Quote:A little further down on the linked Marlin page is a very nice 200step/rev stepper including gearhead. Seems ideal for the application...
Quote:IMHO just buy an EQ-1 motor drive. They are quite cheap.Now they are built for a 100-tooth worm reduction, so depending on the tooth count of your worm, you will need to change the speed. It's easy, just replace the crystal.http://orlygoingthirty.blogspot.sg/2010/06/telescope-mount-hacking.htmlThis has the advantage of being a working system, probably more reliable than anything you can build yourself, and it's cheap. Under $100 for the EQ-1M drive and a couple bucks for the crystal.
Quote:IMHO just buy an EQ-1 motor drive. They are quite cheap.... It's easy, just replace the crystal.