RA axis torque measurement - Engineer required :)

[samtheeagle]

I'm on the verge of ordering the parts I need to try and make my http://stargazerslounge.com/diy-astronomer/104457-diy-tracking-drive.html, but before I do that I'd like to find out what sort of power I'm going to need from the stepper motor. Does anyone know off the top of their head, or could someone measure for me, the torque required to turn the RA axis on a laden EQ3-2 mount (African or European )? I can't do it myself as I've already lent the mount to my brother in law, and I don't have a torque wrench...

The motor I'm looking at currently has a holding torque of 2.3kg*cm.

Thanks in anticipation.

[Merlin66]

Don't have numbers for you, but if the mount is well balanced a 40W motor will do the job. 2.5Kg torque is a LOT of grunt!! It would certainly move mountains and your EQ mount!!

Ken

[samtheeagle]

I'll take your word for it Ken I have no idea, so 0.23 newton meters is pretty strong then?

[FraserClarke]

Back of the envelope (or rather 'back of the quick reply box');

Your motors have a torque of 2.6kg/cm

You're gearing down 1:130 (linked thread), so effective torque of RA axis is 338kg/cm.

Guess that your CoG is ~25cm from the axis, and you can balance the telescope to 1kg (should be possible to do better I suspect). So your mis-balance torque is 25kg/cm. That leaves you ~300kg/cm to cover accelerations, wind loading, etc -- which seems quite generous.

Steppers can have significantly lower torques in certain frequency ranges, but I doubt it would be by a factor of 10. Reckon your motors should be OK

I'm quite tired though -- so you'll want to check the above for silly mistakes

[samtheeagle]

<samtheeagle> bows down to superior engineering skills Once again I'll take your word for it, but it certainly seems that the motor will do the job Thanks both.