[Moon-Net] SPID BIGRAS/HR modification with Incremental encoders

ON4AOI_PDA on4aoi_pda at skynet.be
Wed Apr 7 10:02:44 CEST 2021


Hi Bob,

For me it was early morning when I read your reply …. ..

What I forgot to wrote in previous email is that I use very high shielded cables for the sensors..

The reason why I like changing to Raztrack from Gary N8CQ is that the elevation part is already controlled

By his hardware because my 16ft dish is mounted on a lift that needs some mechanical tolerance. 

>From MR to MS I measured -1 to +2 deg difference.

My lift needs to be parked at 147deg or it can come down and that gives the difference because of the counterpoise.

To correct this difference I made a pendulum with mab25 in a full closed box that indicates the correct Elevation now.

Since Gary has/is been working on adding incremental encoders to his MABMPU boards it

Sure would be an improvement, so instead of following 2 tracking systems I would end up with one 😊.       

 

Concerning the RAS/HR I can accept what SPID writes on their webpage (if it’s true)

because there is a relation between pulses and gearbox ratio.

 

“32 pulses per revolution, and that works out to 8 pulses per degree” this makes sense since

The gearbox ratio for the RAS/HR I owned was 0.125 (*8 = 1deg) . 

 

But the BIGRAS/HR with gearbox ratio setting = 0.093799 remains a mistery to me

 

With the info you gave here below maybe I find the answer now

 

“On the other hand, if the specs were wrong and the sensor on the BIG RAS HR gave 40 pulses per revolution,

you'd end up with a primary reduction ratio of 90:1 (same as RAS HR) and a secondary reduction on 68:1”

 

I can have incremental encoders with 100-200-360-1000-1024-2000-2500ppr and would like to order direct the

Correct one  to have 4096 pulses per revolution to get 0.1 degree resolution.

(This is without counting the reduction ratio’s of the gears)

 

Guy ON4AOI

    

 

 

 

From: Bob Atkins <ka1gt at hotmail.com> 
Sent: Wednesday, April 7, 2021 7:30 AM
To: moon-net at mailman.pe1itr.com; ON4AOI_PDA <on4aoi_pda at skynet.be>
Subject: Re: [Moon-Net] SPID BIGRAS/HR modification with Incremental encoders

 

Hi Guy

 

The HR rotors don't use reel switches. They use hall effect sensors to generate quadrature encoded pulses, 10 per degree with the BIG RAS HR. It's already an incremental quadrature hall effect encoder, so I wonder why you are thinking of replacing it with another incremental encoder? Perhaps you have an early model that's different to the current model? As far as I know only the standard (non HR) SPID rotors use the magnet and reed switch pulse generation method (and 0.5 degree resolution for the BIG RAS, 1 degree for the RAS).

 

I have an analysis fof the RAS HR encoding here :  <https://bobatkins.com/radio/spid_ras_hr.html> https://bobatkins.com/radio/spid_ras_hr.html

 

My understanding is that on the RAS HR (not BIG RAS HR), the hall effect sensor system generates 32 pulses per revolution, and that works out to 8 pulses per degree rotation of the antenna.  You'd then maybe think that on the BIG RAS there would be 40 pulses per revolution and 10 pulses per degree.  The SPID site says 32 pulses per revolution for both of them, but I don't if you can 100% trust that. There are other errors in their spec sheet that I've pointed out to them, but which have not been corrected. It's possible that are both 32 pulses/ revolution and the Big RAS has a different primary/secondary gearing system so between the two gearboxes, 32 pulses/rev of the shaft may correspond to 10 pulses/degree of antenna rotation.

 

I'm not sure what you can get out of the given numbers.

 

The overall gearing ratio (through both gearboxes) is currently given as 4960:1 for the RAS and 6120:1 for the Big RAS

 

So to rotate the antenna once (360 degrees) you would need 4960 revolutions of the RAS HR motor and you would get (360*8) = 2880 pulses. If you get 32 pulses per rotation of the motor, that means  90 revolutions of the sensor shaft and then 55.111111:1 reduction from the sensor shaft to the antenna

 

Similarly to rotate the antenna once (360 degrees) you would need 6120  revolutions of the BIG RAS HR motor and you would get (360*10) = 3600 pulses.   If you get 32 pulses per rotation of the motor, that means  112.5 revolutions of the sensor shaft and then 54.4 reduction from the sensor shaft to the antenna.

 

On the other hand, if the specs were wrong and the sensor on the BIG RAS HR gave 40 pulses per revolution, you'd end up with a primary reduction ratio of 90:1 (same as RAS HR) and a secondary reduction on 68:1

 

I'm not sure any of this helps (or if my math makes any sense when I do it at 1:30am!).

 

I wish SPID provided more extensive documentation on their rotor system products (like a circuit diagram of the controller).

 

73

Bob, KA1GT

 

 

 

 

 

  _____  

From: Moon-net <moon-net-bounces at mailman.pe1itr.com <mailto:moon-net-bounces at mailman.pe1itr.com> > on behalf of ON4AOI_PDA via Moon-net <moon-net at mailman.pe1itr.com <mailto:moon-net at mailman.pe1itr.com> >
Sent: Tuesday, April 6, 2021 2:38 PM
To: moon-net at mailman.pe1itr.com <mailto:moon-net at mailman.pe1itr.com>  <moon-net at mailman.pe1itr.com <mailto:moon-net at mailman.pe1itr.com> >
Subject: [Moon-Net] SPID BIGRAS/HR modification with Incremental encoders 

 

Hi all,

 

Trying to figure out how much revolutions the gearbox makes for 1 deg (AZ or EL) movement

Before I order incremental encoder and determine the correct PPR

Since they (SPID) have used different gearboxes even for the same model it all depend on the gearbox ratio

you have to set in there controller MD01 or MD02 via software. 

Depending on there specifications the BIGRAS/HR has a resolution of 0.1 deg if this true then I expect

10 pulses for 1 deg but without complete demolition of the sensor part I can’t find out how many reed

Contacts there are inside or if its reversed how many magnets?

 

My gearbox ratio setting = 0.093799  

if I would use this for a calculation then you get nowhere  

360 deg / 0.093799 =  3838  

 

Guy ON4AOI     

 

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