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

Bob Atkins ka1gt at hotmail.com
Wed Apr 7 07:29:37 CEST 2021


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

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





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From: Moon-net <moon-net-bounces at mailman.pe1itr.com> on behalf of ON4AOI_PDA via Moon-net <moon-net at mailman.pe1itr.com>
Sent: Tuesday, April 6, 2021 2:38 PM
To: moon-net at mailman.pe1itr.com <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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