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Re: How does RA tracking / guiding work?

 
Edited

Here are my notes on Gemini-1 divisor values from the early 2000's:
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The RA divisor indicates how often Gemini advances the RA motor one step forward. The actual number used for this will depend on the mount, gear ratio, number of gear teeth, etc. From the mounts supported by Gemini Level 3, here are the default rate divisors for Sidereal tracking rate:

GM-8 ? 56096*
G-11 56096
HGM-200 56096
MI-250 56096
CI-700 56096*
Titan50 37398
Titan 37398**

*Note: since Gemini stores divisor rate as a 16 bit number, GM8 and CI700 actual divisor of 112192 is too large to store, so Gemini, instead, uses and reports the divisor value divided by 2, i.e., 56096.

**The same applies to the Titan divisor value: Titan (not Titan50) has the divisor value of? 74794. Again, due to the 16 bit limitation of Gemini, this value has to be entered as divided by 2, or 37398.

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Regards,

? ? ? ?-Paul


On Mon, Jun 21, 2021 at 05:20 AM, Brendan Smith wrote:
oh I forgot to mention the Gemini 1 was 16 bit, so the max 16 bit value was 2^16 = 65,536.?? The titan divisor has a "pre-scaler" computation of "2" to bring the divisor value below the 16 bit limit.??

This is the same for Gm8 and CI-700. ? Its a maths trick to fit the divisors.

The Gemini 2 is a 32 bit controller so it doesn't suffer this yet probably for ease many of the function are probably converted to 16 bit for ease.?? Like the divisors.? The Ra/DEC controllers are 16 bit DsPICs.

Rene' would be best to comment.??? I'd have to use a a logic analyser like sigrok to see.

cheers


--
Brendan
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