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Old 12th Oct 2018, 4:15 pm   #1
Bazz4CQJ
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Default Poor Man's Rotator Using a Stepper Motor?

I dismantled a piece of laboratory equipment a while ago, ending up with a small box full of stepper motors. What I know about stepper motors will go on the back of a postage stamp.

However, I did wonder about the possibility of making an antenna rotator and there are certainly a few hits on Google discussing this approach, while other focus on drivable camera mounts.

Such a rotator will obviously not cope with a 20m 3-element beam but could cope with maybe a mag-loop or a small 2m yagi? I gather that the heart of the system would be either a Raspberry or an Arduino?

Wonder if anyone has been down this path?

B
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Old 12th Oct 2018, 4:43 pm   #2
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Default Re: Poor Man's Rotator Using a Stepper Motor?

You'd need to gear it down quite a lot in order to get enough torque. Steppers - because they move abruptly and in pulses - don't really deal with 'loads' that have much inertia.

A stepper is a good way though of driving a loop-tuning capacitor: the old AEA "Isoloop" used a stepper-motor which drove the tuning capacitor through a toothed belt and pulleys, which provided a good reduction-ratio as well as isolating the stepper from the RF-hot capacitor-shaft (so it didn't upset the electrical balance of the loop).

See here for a breakdown of an Isoloop including the stepper drive: https://frrl.wordpress.com/2009/03/2...-loop-antenna/
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Old 12th Oct 2018, 4:49 pm   #3
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Default Re: Poor Man's Rotator Using a Stepper Motor?

I use a radio control sail winch servo for my loop rotator.
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Old 12th Oct 2018, 6:13 pm   #4
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Default Re: Poor Man's Rotator Using a Stepper Motor?

Thanks for that. Most of these ones have a built-in 50:1 reduction gear box. I'm just working towards getting them turning so that I can grab one and assess just how much/little torque it has.

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Old 12th Oct 2018, 6:16 pm   #5
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Default Re: Poor Man's Rotator Using a Stepper Motor?

If these steppers were in a piece of equipment there would have been drive systems for them - do you have those?

If there are type numbers on the motors you can look up the data and find out what they can do.
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Old 12th Oct 2018, 7:08 pm   #6
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Default Re: Poor Man's Rotator Using a Stepper Motor?

RS Stock No. 443-0102 is a handy module to control a stepper motor.
An external clock would be needed if you want to count the steps.

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Old 12th Oct 2018, 7:41 pm   #7
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Default Re: Poor Man's Rotator Using a Stepper Motor?

Plenty of Chinese ones on ebay, dont know if theyr'e any good though?
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Old 12th Oct 2018, 7:55 pm   #8
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Default Re: Poor Man's Rotator Using a Stepper Motor?

The equipment dated back to the 1970s and was made in Japan and we had no service info for it. It had numerous pcb cards in slot mounts and I guess the drivers were on one or more of the cards, which we didnt keep.

The geared motors dont have makers name on them but I found out that they were made by Sanryusha Co. Ltd, and are types P43G; 12V, Steps: 24, Coil Ohm: 70, G ratio: 1/50. The torque is quoted as just 0.3Nm. Their website is in Japanese only and Google fails to translate the bits Id like. Im still looking on Google for the other motors which have terms Astrosyn, Miniangle and Shinkoh on them.

Thanks for the info on the RS driver.

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Old 12th Oct 2018, 8:39 pm   #9
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Default Re: Poor Man's Rotator Using a Stepper Motor?

Operating a load with a stepper isn't just about getting the pulses to go and stop. You also need to generate an acceleration and deceleration profile otherwise the motor will likely just buzz and vibrate if you apply the required frequency to the driver stage. Very few off the shelf drivers will have this as it's expected to be controlled by a micro controller etc.
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Old 12th Oct 2018, 8:55 pm   #10
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Default Re: Poor Man's Rotator Using a Stepper Motor?

You may also need some form of position monitoring? Counting steps is easy, as is storing the 'last position' for subsequent power ups.
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Old 13th Oct 2018, 7:10 am   #11
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Default Re: Poor Man's Rotator Using a Stepper Motor?

I would think a window/wiper motor may be for your application, easier to drive too.

Andy.
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Old 13th Oct 2018, 7:20 am   #12
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Default Re: Poor Man's Rotator Using a Stepper Motor?

This may be of interest (not stepper motor):-

http://www.sarcnet.org/projects.html...a_Rotator_Mk_1
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Old 13th Oct 2018, 4:48 pm   #13
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Default Re: Poor Man's Rotator Using a Stepper Motor?

Thanks all. Yes, I think my "windfall" of stepper motors may have sent me down the wrong route here. I've been triggered by the thread about 2m to get back on the band after a few years (35?) absence. Today I've put up a 1/4 wave ground plane and I am hearing things on my old FT290 , now I just need to wipe an oily rag over the 10W PA which I have and then I may get out (from a QTH which is in quite a dip).

Re window wiper motors, I actually have a couple of motors from car door windows. The ones I have (I think made by Bosch for Rover) are just incredibly powerful in terms of torque.

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Old 13th Oct 2018, 5:31 pm   #14
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Default Re: Poor Man's Rotator Using a Stepper Motor?

As an alternative to a traditional direction indicator using some sort of positional feedback to indicate the pointing direction of a remote beam, consider mounting a cheap CCTV, or Web, or wireless camera in a weatherproof enclosure on top of the boom looking along it in the direction of fire. That way you can 'see' which way the beam is pointing.

This would not have been a viable option until recently but basic CCD cameras with various types of connectivity are now very cheap.

Of course if this is to be internally mounted then all it will see is the inside of your loft. The camera / associated electronics may also radiate unwanted interference within the band of interest.
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Old 13th Oct 2018, 6:09 pm   #15
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Default Re: Poor Man's Rotator Using a Stepper Motor?

A telescope was often used to read aerial current meters up in the wires.
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Old 13th Oct 2018, 6:09 pm   #16
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Default Re: Poor Man's Rotator Using a Stepper Motor?

Wherever the mast is mounted, the camera could be arranged to see a compass rose mounted in a static location (see 'The Martian'...).
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Old 13th Oct 2018, 6:19 pm   #17
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Default Re: Poor Man's Rotator Using a Stepper Motor?

Quote:
Originally Posted by merlinmaxwell View Post
A telescope was often used to read aerial current meters up in the wires.
I used to use the telescope-thing to a signal-strength-meter located 1/4 mile away from my antennas.

It was always hit-and-miss [the Field-strength-meter was strapped to a 100-foot-high ash-tree and if there was any wind the telescope only saw it for a desperately-small period]

These days I have a field-strength-meter half a mile away, with an old iPhone closely aimed at it. I can call it and switch to video-call mode when I want a strength-reading.

Isn't technology wonderful !
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Old 13th Oct 2018, 8:32 pm   #18
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Default Re: Poor Man's Rotator Using a Stepper Motor?

Quote:
Originally Posted by dseymo1 View Post
Wherever the mast is mounted, the camera could be arranged to see a compass rose mounted in a static location (see 'The Martian'...).
I considered that, but also realised the inside of a loft would usually be rather dark, so you'd need to strap an adapted LED torch to the boom as well, after which further modification the simplicity of a simple feedback pot would start to look increasingly attractive... (Unless you used a camera with a built in IR LED illuminator ring).

For an outside mounted beam with a good view over the rooftops I would assume the operator would have some idea of which visible features lay to the north, east, south and west of their location. This would probably apply even at night as long as there was some streetlighting / other lighting in the general area.

At least one past ICOM mobile amateur radio with a large display screen had the ability to act as a video monitor, possibly with a view to using it as a monitor for ATV, or as a reversing camera monitor.
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