Project:
INDI drivers

Contents:

1. Introduction and setup
2. EQMOD Custom Track Rate
3. EQMOD Custom Gear Ratio
4. To be continued

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!

2: EQMOD Custom Track Rate

These days we have the comet C/2022 E3 ZTF up on the sky. When it closing in it moves much faster relative to the stars and the tracking of the mount doesn't follow it correct, it follow the stars. But there are custom track rate to setup in the EQMOD driver that I wanted to use for this purpose, but it didnt't work. There is something wrong in the EQMOD driver or maybe made for something else, satellites. This will be my first INDI driver project, it doesn't look too difficult for me to correct.

Setup a Custom Track rate:

The Custom Track button set the mount's RA and DEC speed to your choose.

dRA and dDEC speed:

From CdC I get the comet's speed for the day I want to observe it. On my homepage there is a calculator to format the data to fit EQMOD, now with dRA*(DeC) included: Angle conversions.

Set the dRA and dDEC:

When I write in the speeds I get an Error message that it's out of range.

Here I testing with different figures and what's accepted. Clearly there is something wrong, maybe this Custom Track speeds is for satellites that move much faster. But I want to follow the comet and now I'm going to rewrite the C++ code to do this.

Test hardware setup:

When developing the code it's much easier if I can test it directly. I placed my equipment on the floor with the EQ6 mount connected to the Raspberry.

Rewriting the C++ code:

This code is placed in the skywatcher.cpp file which is a part of the EQMOD driver. I found it after looking through the code. There are two places, one for SetRARate and one for SetDECRate. I can see what's wrong, they use the same limits as to SlewTo command, the last is a fast moving and for Custom Track we need a very slow speed.

Looking through the problem and how I can correct this I found the simplest was just to remove the lower limit, the figures are absolute and can never be negative so it's okay.

This line is replaced:
999: if ((absrate < get_min_rate()) || (absrate > get_max_rate()))

With this one
1000: if ((absrate > get_max_rate()))

Now it only check that the upper limit is within range. The lower limit is not needed, it's an absolute value and can never be negative.

I do the same for the DEC Track rate. When I testing the equipment on the floor it looks to work now, I can set small dRA and dDEC speeds without any error alarm. I will change the Error alarm info later when I have tested it outside on a real comet.

This was really good, because I have a much more complicated work to do with Custom Gear Ratio setup.