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Author Topic: Synchronous Motor Replacement  (Read 6822 times)

rzep

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Synchronous Motor Replacement
« on: November 03, 2014, 22:14:14 »

I'm hoping the AstroEQ does what I need. Situation:

My current mount uses Hurst 115V synchronous motors at 1/2 rpm. The mount cannot be modified for goto and I'd like to update to steppers as the synchronous motors are being obsoleted. Don't care about goto or slewing rates, all I really desire is good stepper motor control. I've found direct replacements for my existing motors from the same manufacturer. The motors, however, are 6 wire 4 phase bifilar. I've attached spec sheets with a wiring diagram. The motors I'm looking at are the LSG35012  gearmotor series from Hust. One has 12,000 steps/rev and the other has 14000 steps/rev. With about a 100 - 120  pulse/sec rate, I should get the correct sidereal rate and it should be very smooth.

If you could review and let me know if they would work, it would be greatly appreciated. If the AstroEQ would work, consider me on the buy list!

Thanx!
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TCWORLD

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Re: Synchronous Motor Replacement
« Reply #1 on: November 04, 2014, 01:54:38 »

It should be possible to wire those up as Bipolar (there are two ways of doing it). The disadvantage is a reduction in Torque, but with such a high gear ratio (250:1) that probably won't be noticeable.

If you go for one of the ones that has a nominal voltage of 12V (as opposed to the one rated at 24V), they should be usable. I would go for the 12000 step/rev version as it has a lower gear ratio (250:1 instead of 300:1).

*However* they will likely be very very slow for go-to movements, possibly as little as 10x speeds due to the very high gear ratio.
« Last Edit: November 09, 2014, 05:00:24 by TCWORLD »
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Tom Carpenter (AstroEQ)

rzep

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Re: Synchronous Motor Replacement
« Reply #2 on: November 04, 2014, 13:53:24 »

Thanx Tom, that is the news I was hoping for! Looks like I be asking for one of the available 7 under my Christmas tree, so put me on the list!

2 last questions though

1. Will the AstroEQ work independently of EQmod? Say I just want to use a manual handset in the ST-4 port and not lug out the computer, will it still track at sidereal (or last set) rate?

2. The 812 mount used a 30 sector gear to drive the RA. After 2 hours of travel, the gear would trip a micro switch to kill power to the motor to prevent the RA gear assembly from jamming against the mount housing. By using a sector gear, the drive incorporated the accuracy of a 12" 359 tooth gear into a housing the would only usually fit a 6" gear. I need to incorporate this power kill safety into the drive system. Is it possible to kill stepper motor power directly through the micro switch, or would I have to kill power to the AstroEQ?
« Last Edit: November 05, 2014, 23:38:17 by rzep »
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TCWORLD

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Re: Synchronous Motor Replacement
« Reply #3 on: November 09, 2014, 04:59:09 »

It should be possible to use ST-4 without EQMOD being connected. I think at the moment EQMOD has to be connected initially to start the controller running before ST4 will work standalone, but that is something I plan to address in the firmware (if the controller is not initialised and receives ST4 input, then autoinitialise it without EQMOD).

There isn't a simple way to make the microswitch shut down the controller. I could add into the firmware code which issues an emergency stop when one of the spare I/O pins goes low for example. That way EQMOD would know that the mount has stopped moving.
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Tom Carpenter (AstroEQ)

rzep

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Re: Synchronous Motor Replacement
« Reply #4 on: November 09, 2014, 16:18:24 »

Thanks Tom! I like the firmware shutdown version much better. The other option was to have the safety switch kill power to the AstroEQ. I really didn't like this option as I don't like electronics rebooting and reinitializing the time. I would be more then willing to pay for the additional costs of adding those lines of code. So, it actually looks like I'll be able to get this project off the ground. Do you actually want me to put an order in, or what should I do at this point?

For your information, as a source of parts in the US, I would look at Newark Electronics which appears to be a US extension of Farnell. Another good source is Mouser Electronics.
« Last Edit: November 09, 2014, 16:23:42 by rzep »
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TCWORLD

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Re: Synchronous Motor Replacement
« Reply #5 on: December 13, 2014, 01:48:12 »

Hi,
I'm going to look into whether or not I can add the emergency shutdown stuff to the code while I am back in the UK over Christmas, will let you know how it goes. The next batch of controllers will be available the first week in January also.
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Tom Carpenter (AstroEQ)

RussellsTeapot

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Re: Synchronous Motor Replacement
« Reply #6 on: January 01, 2015, 20:01:13 »

I have some Sanyo Denki steppers that I'd like to use. 

The problem is that I can't find these exact motors listed anywhere, and as a result, I don't know the voltage for them.

I am going to make the assumption that there are people here who may know where I can find this information and point me towards it.

So, I have a few Sanyo-Denki steppers labelled as:
DC 2A, 1.8 DEG, Type 103H7123-0447 .  There is a "Lot number" as well, but I suspect it's not significant, as it varies from motor to motor.

Thanks for any help anyone can render.

Roger
Canada
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TCWORLD

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Re: Synchronous Motor Replacement
« Reply #7 on: January 01, 2015, 21:07:31 »

It seems like they are similar to these:
http://www.newark.com/sanyo-denki-sanmotion/103h7123-0440/stepper-motor-2-phase/dp/25M0229

In which case they are unipolar, 3.2V/phase and 2A/phase. Being unipolar isn't the end of the world, there are ways of wiring them so that they behave as bipolar motors. However the current rating far exceeds the 1.5A absolute maximum for AstroEQ. They can be run at a lower current, but with a loss of Torque/Max speed. This may not be an issue as small telescope mounts don't tend to require a lot of torque to drive them due to the high gear ratio worm.
« Last Edit: January 01, 2015, 21:11:46 by TCWORLD »
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Tom Carpenter (AstroEQ)

RussellsTeapot

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Re: Synchronous Motor Replacement
« Reply #8 on: January 01, 2015, 22:06:09 »

Hmmm...so, not ideal, then.

What would the ideal motor look like?  Perhaps it may be possible to either sell the ones I have to, or swap them with, some robotics geek.

Thanks, Tom.
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