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Single axis motor drive for EQ3-2 and EQ4 mount – FAULTY – incorrect gearing Cheshire Collimator for Newtonian Telescopes – Long Version
Single axis motor drive for EQ3-2 and EQ4 mount – FAULTY – incorrect gearingClick images to enlargeDescription
Ah, right. These are not quite what we were expecting. They do work but unfortunately somebody got their maths wrong with the gearing and they run twice as fast as they should so only look on these as a project or for spare parts.
Maybe the handset is useful to you or perhaps you could make your own electric focuser although you will have to remember to switch off the power as it will carry on as if it was a RA motor.
The instructions tell you that it must only be used on a 6 volt supply but they include a battery pack that takes 6 batteries. We checked that with the supplier and these motors are quite safe to use on 9 volts.
Please note that the brass driving gear has intentional flexibility built into is so that, although it appears to wobble on its axis (a definite touch of axial precession), it allows for a slightly off centre drive connection. The motors are usually held against the drive cog by with fairly stiff spring hence the wobble doesn’t matter. You will have to take that into account if you are going to use it in a project.
Here’s a report from Tony who examined one closely:
“
The instruction sheet, you enclosed i think belongs to a slightly different but similar unit.It says that the supply voltage should not exceed 6.4 volts. The battery holder holds 6 x 1.5 v batteries which would be 9vI tried it using a 6 volt DC power supply and it worked without the low voltage light illuminating. I did also notice that the DIN plug (theres a thing I haven’t seen for a while!) had some breakage on the strain relief. I ran the motor for a couple of hours to monitor the speed and it runs at 0.4957 rpm. Although under no load, I believe these are stepping motors, so speed should not be affected by load ( until the load becomes excessive). The motor output gear is a 24 tooth 0.75 module and the larger gear with clutch is 60t giving a 2.5:1 ratio giving a speed of 0.19828 rpm. These must be for a different mount as the clutch did not fit and the gear alone did not properly either (loose fit). Also there was no spring or hook to keep the motor in mesh with the gear on the RA shaft. some modification would be required to get every thing to line up and run true The sidereal speed of the RA axis is 1/1436minutes = 0.00069638 rpm, so the mount that this drive would be suitable for would need 0.19828/0.00069638 = 284.7 so lets say 285 turns of the RA shaft per sidereal day. This seems a high number compared to any RA ratios I’ve seen from searching on the internet. My Skywatcher EQ2 mount needs 138 turns per sidereal day which is approximately half of the 285 so the mount would move more than twice as fast as required. The mount has a very fine toothed gear mounted on a tapered end to the RA drive shaft The gear from my measurement is 140t x 0.35 module (49 mm pcd) so the nearest matching gear would be a 27 t x 0.35 module which would be about 10 mm OD. (9.45 pcd). I haven’t found such a size easily available and I suspect it would be unreliable because the cantelevered output shaft of the motor is very loose and wobbly and would easily loose mesh with the tiny teeth. it would need a spring to maintain mesh. Another avenue to reduce the speed would be to change the drive crystal /oscillator or the drive electronics but that would need the box opening up. I hope this provides you with some help in identifying which mounts it would fit.”
So, there you have it. Only bid if you know what you are getting as we don’t want it back.
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Category: Cameras and Photography:Telescopes and Binoculars:Telescope Parts and Accessories:Other Telescope Parts
Location: Welwyn Garden City