Re: Mach2 Guide rate and question about gear meshing.

Roland Christen

The guide rate for all our mounts is recommended to be 1x. This allows the guiding loop to move the guide star in the most efficient manner back to the zero point without delay. This works perfectly with all of our mounts. Guiding at slower rates is not recommended.

The movement of the RA axis suggests that the backstop adjustment is a bit loose, but it has zero effect during actual operation. When the motors are active they will counter this and stiffen up the axis. On any spring loaded mount there is a small amount of pressure that pushes the worm into mesh with the worm wheel teeth. That pressure cannot be really heavy because it will wear the worm teeth at a high rate during slewing. For longevity we set the spring pressure high enough to ensure good contact, but not so high to cause excessive wear. As a result, the worm teeth can be made to back up slightly until the mechanism hits the backstop - that's the click click that you hear when you push the axis back and forth. You can see the action of the mechanism and the backstop if you remove the rear cover of the motor box and look inside.

Now it is possible that something else is loose, a very distant possibility would be the end play adjustment of the worm , but by the sounds of it, the backstop is set a bit too high. Offhand I cannot find your name on the list of mounts we shipped, so always include a serial number whenever you report any issues, if you can. If it is the backstop, that is easily remedied with a simple adjustment. It won't change how the mount operates in practice. I can send you some instructions that shows how the backstop is adjusted. But first, open the motor box cover and look inside.

None of this will affect your tracking, pointing or guiding in any way. Once the power is turned on, the encoders take over and keep the axes rigidly pointing to sub-arc sec levels to the place in the sky that you point your scope to. Regardless of weight or even imbalance. Of course the first reaction to any anomaly is to question tracking, guiding, pointing, etc., but i can assure you that it's a red herring.

Roland Christen
Astro-Physics Inc.

-----Original Message-----
From: Micheal Fields Jr via <mpfjr@...>
Sent: Fri, Feb 12, 2021 1:09 pm
Subject: [ap-gto] Mach2 Guide rate and question about gear meshing.

What is the recommended guide rate setting?  My experience with premium mounts is that you reduce the guide rate.  The other mount I am using recommends .20 or .25 and I've been pretty happy with that.  

I think I saw somewhere the recommended with the Mach2 is 1.0x?  

But maybe your experience is different and you have a different value. I am using the latest nightly PHD2 with multi star guiding.

Next question is about gear meshing.  Specifically the RA.   I had rain predicted for today so I brought my gear inside and set it up in my kitchen so I could work on my camera spacing with a new precise parts adapter that came in the mail yesterday.  While I was carrying the mount into the house the saddle plate was up against my tummy and I could feel something that felt loose.  When I set it back on the tripod and bolted everything down tight, I  could wiggle the saddle and feel something click/clack .  I then followed the movement by eye and could see the entire RA had some movement.  The alignment marks for RA showed a bit of movement.   I didn't notice this before.  Now if I hold on to the OTA and wiggle it, I can hear it click/clack as it moves.  The weight is far under capacity with a C11 and a one shot color camera.  No filter wheels or rotators etc.    Here is a short video showing what I am experiencing.   What is interesting is that when making a model I was noticing some results that I thought were very strange depending on what side of the meridian it was  on but I assumed it was the fact I focus with my primary mirror so it moves.  However guiding was less than amazing too but again I had an excuse which was clouds moving in and that messes with the  guide stars.   So please take a look and tell me if this is normal.  Thanks!   Note: if you turn your volume up or use headphones you can hear it too.

Roland Christen

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