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Author Topic: Need help with Declination axis Stepper Motor.  (Read 1184 times)

RAF_Blackace

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Need help with Declination axis Stepper Motor.
« on: August 27, 2018, 20:55:10 »

Hi.

I am changing my DC motors on my equatorial platform to steppers but am having trouble finding one for the declination axis that conforms to the requirements.

This motor raises and lowers around 50kg through a lead screw and has an effective worm gear ratio of 1:3600

It requires around 2N/m torque to drive it reliably (1.4 N/m normally). I can use anything from 1:5 to about 1:20 gearbox for this stepper motor to get the required torque.

But the only motors that fit this are Nema 17 motors at 1.68 amps per winding.

I was wondering, since this motor seldom runs, and it should need no holding power since the platform would not move if the motor was switched off. Is there anyway I could use the DRV8825 to drive it? I know the driver would get hot, but it can supply more then the 1.2 amps if it only needs to do so infrequently.

I have no intention of slewing the drive, it's an equatorial platform after all so it's not possible to do that. All the declination motor would be required to do is to adjust the Dec axis during auto guiding. So it would probably run no longer than 10 seconds every few minutes or so.

What do you think?

Or does anyone know of a NEMA geared stepper with a gearbox anything between 1:5 and 1:20 that gives 2N/m at the gearbox output and draws around 1.2 amps a winding?

thanks for the help.

« Last Edit: August 27, 2018, 21:13:04 by RAF_Blackace »
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RAF_Blackace

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Re: Need help with Declination axis Stepper Motor.
« Reply #1 on: August 27, 2018, 21:10:25 »

This is a picture of the current arrangement with a DC drive. This drive needs changing to a stepper motor.
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RAF_Blackace

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Re: Need help with Declination axis Stepper Motor.
« Reply #2 on: August 28, 2018, 00:53:59 »

I think I may have found one that may do for what I want.

I would still like to know if it is possible to use the 1.68 A NEMA 17 motor though if it is only used infrequently?

https://www.ebay.co.uk/itm/Nema-14-Stepper-Geared-Motor-19-1-Planetary-Gearbox-0-8A-CNC-Robot-3D-Printer/122599591491?epid=1544836688&hash=item1c8b814e43:g:DRAAAOSw~ElZaXn1
« Last Edit: August 28, 2018, 15:16:17 by RAF_Blackace »
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RAF_Blackace

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Re: Need help with Declination axis Stepper Motor.
« Reply #3 on: September 16, 2018, 01:41:28 »

good news, the 0.8 amp motor is fitted and works fine.

Everything is finished with the platform, all I need now are some clear nights. :)
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