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[tyson]

As I mentioned before, I intend to try to retrofit the an old Meade Starfinder equatorial mount with 2 steppers and an AstroEQ. 


For the declination axis, I can mount a 60T timing gear to a 15T pinion on the stepper.  Using gears and belt from Servocity and the NEMA 14 stepper and bracket from Pololu.  The bearing collar, servo arm clamp are custom machined to adopt onto features already machined into the Meade mount. 

NEMA 14
https://www.pololu.com/product/1209
General specifications
Shaft type:    5 mm "D"
Steps per revolution:    200
Current rating:    1000 mA2
Voltage rating:    2.7 V
Holding torque:    20 oz·in
Resistance:    2.7 Ohm2
Inductance per phase:    4.3 mH
Number of leads:    4
Lead length:    30 cm




On the RA axis, there is already a ~4" gear and worm gear pair.  I am replacing the 120VAC vintage clock drive motor with a NEMA 11 motor.  It seems theres only space for a NEMA 11 if i want to fit in the same enclosure and I will have to have the shaft custom machined due to the worm gear end.  I'm sort of wondering if its even worth the bother to fit a small motor, made expensive because of the custom shaft.  But I dont mind if someone (Tom?) can confirm the torque and specs are compatible and sufficient.  If not, then I should be able to create custom machined brackets and coupler to fit a larger stepper in there since I'm not space constrained, but definitely more complicated.



NEMA 11 28x32
https://www.pololu.com/product/1205
General specifications
Shaft type:    5 mm "D"
Steps per revolution:    200
Current rating:    670 mA2
Voltage rating:    3.8 V
Holding torque:    8.3 oz·in
Resistance:    5.6 Ohm2
Inductance per phase:    4.2 mH
Number of leads:    4
Lead length:    30 cm

Any thoughts before I go and buy the parts?

I intend to mount a AT6RC Astrotech 6" richey.  Not sure what kind of guiding yet. 

[TCWORLD]

If there is room for a slightly longer NEMA11 motor, these are the ones I use on my mount: https://www.pololu.com/product/1206
They are still NEMA11, but 45mm long, and have about 50% more torque than the other one.

My mount is an EQ5 with 2.666667:1 belt drive and 144:1 worm ratio. With the motors in the link I posted, I can get ~400x speeds reliably with a 120mm Refractor and DSLR (with both axes balanced). So if you use 60:15 that will give you a higher gear ratio which will give you a bit more torque than I get. Not sure what scope you have.

How easy is it to turn the worm by hand when the scope is attached? If even with the scope the worm is easy to turn by hand, then you'll probably be fine with the NEMA11. It's hard really to say for sure.

[tyson]

Thanks for your thoughts.  I'd like to try to keep the motor within the enclosure if i can.  I'll try the smaller 11.

Because of the custom shafting for the RA gear, I may buy the motor from another supplier. 
http://www.linengineering.com/stepper-motors/211.aspx

Which model 11 would work best in regards to the difference in resistance/phase or amp/phase?  What is the voltage of the power supply?  [nvm i read 12V]

[TCWORLD]

Generally, the lower the voltage rating of the motors the better - as long as the rated current is <1.5A. This is because motors with a lower rated voltage generally have lower inductance which means they don't lose torque as much at high speeds. The stepper motor drivers on AstroEQ will automatically regulate the voltage to ensure the current stays below its rated level (set by the current limiter).

[tyson]

Thanks. I'll ask for the -02 with the lower voltage and inductance spec.

[tyson]

btw i ended up just ordering the servos from pololu.  linengineering was going to charge me $150 for a modified servo and another servo distributor said they couldnt do it. 

im just going to have my machinist grind the ends as needed.  for 1/10th the cost its worth trying.