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Author Topic: Cheap rotator or DIY?  (Read 12004 times)
G7DMQ
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Posts: 40




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« Reply #30 on: March 14, 2013, 12:05:17 PM »

Thanks for the info, can you please provide the model servo? I looked and there are so many.

That's kind of the point - there are enough that you can size the servo to the job.

My tuner servo is a Futaba 3003
http://www.ebay.co.uk/sch/i.html?_nkw=servo+futaba+3003&_sacat=0&_odkw=RC+servo+futaba+3003&_osacat=0&_from=R40

The rotator is unbranded but is very similar to this:
http://www.ebay.co.uk/itm/Sail-Winch-Servo-55g-metal-gears-10-63kg-torque-6-Turns-travel-/360585176942?pt=UK_ToysGames_RadioControlled_JN&hash=item53f48d276e

Which is rated at 1Nm torque and runs 6 turns - so could achieve 6Nm torque if geared down.  eBay also has two turn winch servos which you could almost connect direct.

The servo tester I bought was something like this:
http://www.ebay.co.uk/itm/Etronix-3-Mode-Servo-Tester-RC-Car-Heli-Boat-Plane-/281077503365?pt=UK_ToysGames_RadioControlled_JN&hash=item4171865585

You don't need any positional feedback as the direction is directly proportional to the position of the knob on the tester.  The servo will keep trying until it achieves the desired position.  So long as the servo is sized for the torque required, it will get there!

If you wanted feedback, you could use another servo and tester with the tester connected to a pot on the antenna - and another servo moving a needle on a compass in your shack - but I don't think it's necessary!  You'll soon trust it to point where you turn the knob!

Si
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CHRISDX
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Posts: 244




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« Reply #31 on: March 14, 2013, 12:11:51 PM »

Hey Si, thanks.

Now I get the idea.

I'm surprised that small of servo would turn the mast. I was thinking a 1/4 scale servo or whatever large size would be needed.

The servo tester knob gives position.  Now if the servo turns six times how does that translate to one turn of the mast and does that mean one turn of the knob to one turn of the mast?

IIRC you have a belt from the servo wheel to the mast, is there a 6:1 diameter ratio between those two to keep the tester knob in sync with the mast direction?

Any pics you could share would be great!
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G7DMQ
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Posts: 40




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« Reply #32 on: March 14, 2013, 01:02:53 PM »

The knob on the tester is connected to an ordinary variable resistor with 270 degree rotational travel.  This coresponds to the full rotational travel of the servo connected.

If its an ordinary servo, that's 180 deg.  If its a winch servo, 6 turns (in this case).

So, you turn the knob 270 deg and the servo turns 6 turns proportionally.

Si
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CHRISDX
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Posts: 244




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« Reply #33 on: March 14, 2013, 01:05:51 PM »

how does six servo turns equate to 1 mast turn though?
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G7DMQ
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Posts: 40




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« Reply #34 on: March 16, 2013, 05:00:26 PM »

That's what the pulleys / toothed belt is for!

Mount the antenna on a bearing and attach the big pulley to the antenna.  Mount the servo to one side connected to the little pulley.  It doesn't need to be geared 6:1 necessarily but if it were, 6turns of the motor would give one turn of the antenna.

Si
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CHRISDX
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Posts: 244




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« Reply #35 on: March 26, 2013, 01:57:42 PM »

ok any chance we can have a pic of how this was implemented?  and a source for the gears and the belt?  thanks!
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G7DMQ
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« Reply #36 on: March 28, 2013, 09:38:34 AM »

OK, I'll see if I can get into the attic at the weekend and take a photo.

The pulleys & belt came from eBay - something like this:
http://www.ebay.co.uk/itm/HTD-5mm-Pitch-Timing-pulley-for-15mm-belt-20-tooth-CNC-ROBOTICS-/221012709019?pt=UK_BOI_Industrial_Automation_Control_ET&hash=item3375624e9b

I bored a hole in the bigger pulley which the bottom of the antenna would fit through tightly - then glued it in place.

The servo came with an circular 'horn' (plastic bit which screws on to top of servo shaft).  I glued the smaller pulley to this and secured it with a couple of small self tapping screws in to pilot holes.

Bracket for servo was just made out of folded Aluminium sheet held to mast with a U bolt.  Nothing fancy!

I'm going to make another one for a new loop - so maybe I'll just take photos of that as I make it!

Si
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CHRISDX
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Posts: 244




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« Reply #37 on: March 28, 2013, 10:00:01 AM »

Very cool info and the pics will be great thank you so much this is a super idea to add to the Rotor choices.    Grin
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G7DMQ
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Posts: 40




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« Reply #38 on: March 29, 2013, 06:04:31 AM »

OK, just for Chris.....
http://www.youtube.com/watch?v=D1DMO98Xuy0
I've uploaded a quick video of construction and operation.

The actual winch servo I have is a Hi-Tec HS-785HB.

The whole rotator weighs just over 1/4Lb and produces plenty of torque and will rotate the antenna 360 deg in 6 seconds - so not too bad.  It will also give better than 1 degree positional accuracy.

Si
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K0JEG
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Posts: 672




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« Reply #39 on: March 29, 2013, 06:11:13 AM »

Thanks for posting the video. I noticed some movement on the servo bracket when first starting up, maybe put a rubber shim in the U bolt? I use old bicycle innertubes. Just anything that can get some grip instead of metal on metal.
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G7DMQ
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Posts: 40




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« Reply #40 on: March 29, 2013, 06:22:16 AM »

It was just a test with the bracket zip-tied to a bit of metal.

If you use a couple of U bolts - it will not move at all.

The hole in the centre of the big pulley is 30mm which fits over the support for the antenna.  This sits over the top of the mast which is 1" diameter, sleeving over the top 3' or so.  Bracket will bolt to mast below that with the pulley on the very bottom.

The weather is too horrible today to install it - but you get the idea.

Si
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CHRISDX
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Posts: 244




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« Reply #41 on: March 29, 2013, 09:43:19 AM »

Hi Si,

thanks a million. picture worth 1000 words as they say.

so this system has not been installed in weather (rain wind) yet?
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G7DMQ
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Posts: 40




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« Reply #42 on: March 31, 2013, 10:19:47 AM »

This one, for the time being is going in the attic above my workshop.

Here's todays project:
http://www.youtube.com/watch?v=jVnCmJu49jw

I had a micro-controller from a company called ByVac which has a 4" touch screen - which I thought would be useful.

I now have it controlling both the direction and tuning of the loop by touching the screen.

Seems to work pretty well and is silent RF wise on HF up to 21Mhz, then you can hear the rotator moving - but it's quiet.  Maybe the servo needs a choke or something.

At the bottom of the screen there is a compass display with a red dot showing the direction the antenna is pointing.  you just touch the display to move the dot to where your finger is - or drag it to move slowly.

The buttons at the top are to fast & slow tune the VC.

There are another two buttons on the left which calibrate the rotator - you point the antenna north, click N then south & click S and it works out the calibration for the dial.  This bit doesn't actually work yet - but there's always tomorrow!  I didn't bother as it seemed to be spot on with my initial values, by chance.

Longer term the plan is to put it on the mast with a 2m Yagi - but I've not built the Yagi yet.

Si
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K0JEG
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Posts: 672




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« Reply #43 on: March 31, 2013, 04:13:43 PM »

Wow that is very good. Thanks for posting.
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G7DMQ
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Posts: 40




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« Reply #44 on: May 06, 2013, 07:25:23 AM »

Another quick video which shows how fast it will move an antenna weighing about 10 Lbs and 5' diameter supported on a push-up fibreglass mast about 30' in the air.

http://www.youtube.com/watch?v=FrVEHKQdra0

Today I've been playing with a HexBeam type thing which weighs about the same - but obviously the mass is further from the centre so has more rotational inertia.  However it seems to move with similar speed & acceleration.

I'll post up a video of that once it's finished & transmitting.

Si
« Last Edit: May 06, 2013, 07:29:16 AM by G7DMQ » Logged
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