Dish pan/tilt head using stepper motors

[VK4GHZ]

Hi all

While I can get my head around microprocessors and digital guff, I often struggle with mechanical things!

I want to construct a pan and tilt head for a microwave dish (65cm offset), but based upon stepper motors for azimuth and elevation.
Initially, control will be rudimentary via switches (up/down, CW/CCW).

Next phase will employ a black box that steers the thing to any desired bearing.
(That is another future topic, once the head is working)

Can anyone please suggest on how to use stepper motors, specifically;
Would models would I consider using - that are actually available to us in this part of the world, without costing an arm & leg?
How would I form them into a working pan/tilt arrangement, maybe with gearing etc?

If you imagine something like a hobby servo based pan/tilt head on MEGA steroids!
Probably a bit like one of these fancy telescope mounts, but with a much greater load capacity, (given a dish reflector can make a nice sail in the wind!)

It's always appreciated if you can provide actual links to things you refer to.

Thanks in advance.

[VK2OMD]

Hi all

While I can get my head around microprocessors and digital guff, I often struggle with mechanical things!

I want to construct a pan and tilt head for a microwave dish (65cm offset), but based upon stepper motors for azimuth and elevation.
Initially, control will be rudimentary via switches (up/down, CW/CCW).

Next phase will employ a black box that steers the thing to any desired bearing.
(That is another future topic, once the head is working)

Can anyone please suggest on how to use stepper motors, specifically;
Would models would I consider using - that are actually available to us in this part of the world, without costing an arm & leg?
How would I form them into a working pan/tilt arrangement, maybe with gearing etc?

If you imagine something like a hobby servo based pan/tilt head on MEGA steroids!
Probably a bit like one of these fancy telescope mounts, but with a much greater load capacity, (given a dish reflector can make a nice sail in the wind!)

It's always appreciated if you can provide actual links to things you refer to.

Thanks in advance.

There is a large range of stuff on eBay, motors, drivers and accessories. It is mostly intended for CNC application, but is adaptable.

There are stepper libraries for Arduino (a microcontroller sytem for kids who apply it to robotics etc... yes, using stepper motors amongst other things).

I mentioned in a recent post, inexpensive flight controller boards that have gyros, accelerometers, and mags on board which may provide a ready framework for a controller. These things are setup for driving brushless DC motors via an ESC, but would have enough pins to drive a pair of stepper motors via a driver board for increased current drive and management of coil current (eg using the Toshiba chip).

Owen

[VK2GOM]

Hi Adam,

Do they specifically have to be steppers? For what reason? Unless you are running absolute encoders with them, it can't be for remembering their position... You would also need some fancy gear train for them.

Just a suggestion - what about an antenna rotator? Ready made mechanicals, good gearing, solid, easy to mount. And if you really wanted to, I'm sure you could probably modify the motor inside for a stepper.

I'm just wondering why seemingly re-inventing the wheel is the perceived way to go?

A lot of scope mounts these days use DC servomotors with encoders to keep track on their position. Steppers in that application are a bit 1990's.

I have one of these; it will carry anything!

73 - Rob VK2GOM / GW0MOH

[VK2OMD]

Backing up a level, what sort of backlash can you tolerate, what sort of gear train can do that? Do you want a lashless drive with counter rotating motors? Brushed DC motors should not be dismissed out of hand... there is not much using have fine step resolution with a stepper if the drive train has much larger backlash.

Owen

[VK4GHZ]

Thanks for the responses so far.

I'm familiar with eBay!
It's searching for the right things, using the correct terminology, and with a working knowledge of how these mechanical things can be used together.

I don't want to steer off topic (no pun intended!), but eventually the controller will most likely be a Raspberry Pi, along with a GPS and digital compass module.
It will know where I am, which direction the mount is facing, and will be able to compute a desired azimuth, based on keyboard entry of a target grid square.
Whether I really need elevation control is questionable, but while we're at it, why not!
Maybe tracking a moving plane or a storm cloud might be on the crazy list in the future?

So let's just assume we will have a black box generating whatever signals are required to drive whatever motors.

Now, back to the mechanical part...

The idea of stepper motors was the first thing to pop into my tiny brain!
I don't care what type of motor is doing the job, just provided I can steer it... which of course requires a feedback path to the controller.

The mechanics need to be affordable.
Not looking at spending thousands of dollars on a telescope mount (?), but would like replicate something like that on the cheaper side.

Backlash?
Say < 1 degrees, preferably < 0.5 degrees.
I'd like this to be usable for 24 GHz, with an inherently sharp pattern.
In my mind, this immediately rules out ham quality rotators... probably satisfactory to several degrees, but.

I have seen a VK7's dish rotation system based on lathe vernier do-hicky, and whilst super-fine manual control is dead easy, but I want to be able to automate this mount.

I will Google "lashless" (my opening sentence should have indicated 101 level of terminology required!)

I should have mentioned, it needs to run off 12V DC for portable operation.

Ideas?

[VK2OMD]

Search eBay for "Toshiba stepper" for drives based on their chips.

You could control one or two axes from a Raspberry Pi GPIO pins. I guess it is not mission critical, so Raspberry Pi is probably ok.

But, I think you have the cart before the horse. You haven't specified, but you probably know, the type of mount, the range in each axis, the resolution and accuracy, and tolerable backlash (due to motor operations or wind).

Obviously, elevation or something like it is needed if you want to do moon bounce or satellite, but some level of elevation control may be useful for terrestrial shots as trophospheric reflection may be at elevation > 0.

One form of 'lashless drive' is counterrotating drives, so they hold the platform in a position between the two drives. In a simple implementation, it uses more power, and you will need some sort of sensor on board to sense the platform pointing to position the platform between the two drives.

If you only need a small range of rotation, the screw actuators used on satellite TV systems are pretty cheap. If you want it for an application where you can rapidly and accurately face any direction, full 360° rotation with <1° accuracy will be a challenging but fun project.

Anyway, read up on the Toshiba chips and what they do for you. You can buy some real cheap stepper motors with gearbox and drivers... I think I paid <$2 each for some for a friend... but last time I looks they might be double that (http://www.ebay.com.au/itm/1pcs-Stepper ... 5d45489f91 - get the ones with the LEDs on the driver board). Again Arduino is a simple instroduction to the things... a nano at about $10 has a USB interface and enough pins and power to mess with a stepper of this type. This motor is not going to turn your antenna, it is probably intended for an air condition stirrer... but you can learn lots for <$20. A friend is using a couple of these for an ATU, one driving a variable cap and the other a roller inductor (though at 12V, you cannot leave full voltage applied to the coils when not stepping... but that is usual).

Owen

[VK2FAK]

Hi all...

Interesting project....what is the estimate of the ( no wind ) weight ..This is going to be your starting point to determine what sort of motors you are going to need..

Simple motors with gearing and quite a few Kg torque can be obtained from Jaycar....


John

[VK4REX]

Hi Adam

Will talk to you tomorrow at Redcliffe. I have just ordered (from Fleabay) some 1RPM 6 volt motor/gearbox combo's. I intend these to to rum under PWM control and H bridge drive to control my AZ/EL mount for the transverters. At $18 dollars each these cheap babies will drive a truck around.

rex

[VK4GHZ]

Will talk to you tomorrow at Redcliffe. I have just ordered (from Fleabay) some 1RPM 6 volt motor/gearbox combo's. I intend these to to rum under PWM control and H bridge drive to control my AZ/EL mount for the transverters. At $18 dollars each these cheap babies will drive a truck around.

rex

Hi Rex
eBay link please?

It would be preferable if you can post more details here.
Others are interested as well.
W.O.R.M.

[VK4REX]

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... OU:AU:3160

[VK4GHZ]

Having considered the potential dicking around with various motors and gearboxes, I'm actually now looking at commonly available sat dish positioners.
Der!
Appropriately geared to handle the wind loading of ~120cm dishes, so no issues there.
Not super expensive.
Power and data up the one cable.

It will be easy to get a micro to generate the 22 kHz pulse train and send commands to the motor.
From my brief look at the DiSEqC protocol document, it may be one way comms, ie; open loop, with the motor being told to go to position x without the feedback to the controller.
I could wrong, pending a closer look into this.
(And there's various versions of DiSEqC)

Who cares anyway, my sat dish positioner has reliably swung my 90cm Ku dish from D2 around to, and hit, PAS8 every time for years now... so if there is no feedback involved in this, it shouldn't be a real problem (as against a perceived problem!) for activity day terrestrial work either.

Depending on model, rotation appears to be limited to 140 - 160°.
I can live with that.
Except for building up a controller/interface/software (the easy bits), the mechanical bit is virtually bolt on and play.

Cheap enough to experiment with at least... and if it does the job, great.

[VK2OMD]

Having considered the potential dicking around with various motors and gearboxes, I'm actually now looking at commonly available sat dish positioners.
...

You may need to alter or make your own bracket for 90° lat (though I think some manufacturers have a high latitude range on their brackets).

So, that adapts the H-H positioner for about 180° of azimuth in an AZ/EL config.

A simple way of getting some elevation adjustment would be a positioner jack in the rear tripod leg (though it is obviously not purely an elevation control).

Owen

[VK4ABD]

May or may not be helpful, this posted to hackaday today http://hackaday.com/2013/11/04/open-sou ... e-control/

[VK3XDK]

Hi everyone,
there is so many "new" devices/transducers available (ie electronic compasses)
I wonder if some could be applied to this use? Be nice to just "plonk" a tripod down and allow the software to do the rest!

[VK2GOM]

On the telescope theme, why not just look for an old Meade LX200 fork mount? Plenty take the telescope out to put on another mount when they realise the limitations of an Alt-Az mount for astronomy, but this is when they'd become useful to you. I sold a fork mount years ago, but can't remember how much I asked for it.

They'd probably appear now and again on the Ice In Space forum, and Astro Buy Sell page.

73 - Rob VK2GOM / GW0MOH

[VK3XYX]

I see that no one has posted anything on this topic for quite a few months, so I guess that we have all seen the article in January QST --- WRAPS: A portable Satellite Antenna Rotator System.
Seems like this would do what Adam wants, but maybe a bit light on for a dish.

Garry VK3XYX