Re: Recent encoder discussion on CN

W Hilmo

I have posted a fair amount of stuff to that thread regarding encoder operation on Astro-Physics mounts, including the AP1100/AP1600 and the Mach2.  I hope that it’s been accurate – and I am always happy to make corrections if I am wrong.


I am pretty sure that most of what Ross has said below is something that I addressed earlier.  The issue is that so much has been said in the thread already, that I don’t know that another long response is going to help…


From: <> On Behalf Of Roland Christen via
Sent: Thursday, February 25, 2021 12:18 PM
Subject: [ap-gto] Recent encoder discussion on CN


This post has a bit of misinformation about encoders on our 1100/1600 mounts, and I need to clarify how the encoders actually work:



Sounds way too complicated to me. When I even suspect that one of my Paramounts is lost, I just home the mount and I'm done with it. Doesn't matter how many times I've moved the axes or lost power or anything else. I just home the mount. After homing the PEC is still perfect. 


I use a 50 year old system that we upgraded to absolute encoders. That beast has all sorts of old age problems but when it stalls or I get the dreaded "lost contact" message. I just reconnect and go on from there. If one of my partners parks the mount by hand, same thing. The mount figures out exactly where it is. 


The fact is that AP had to put the encoders on the 1100's where they would fit and it's the wrong location. You would not have to do any of this with a Mach 2 which was designed from the beginning to be an encoder mount. Same thing with a 10 micron or a Paramount MEII.



First, the 1100 mount encoders are not in the wrong place. They are attached to the axis shaft where they monitor and control the axis position and rotation. The upper part of the mount is a "Lazy Susan" mechanism which can be rotated independently from the axis shaft and then can be locked into place via tightening the clutch knobs. The axis shaft and the worm wheel are one piece machined out of a single billet of high grade aluminum (it is the most rigid and accurate way to form a worm and axis for a telescope mount). The clutch is simply a way to lock or unlock the upper "Lazy Susan" mechanism to the actual axis. You can permanently lock the scope to the axes by tightening the clutch knobs fully, and you basically have the same configuration as a Paramount MEII. That is, you have a clutchless mount which you can unlock via the motor box locking/unlocking mechanism, and you can do your fine balance, or just move the mount to another position in the sky WITHOUT losing your position.


That's right, the encoder mount always knows where it is if you set it up this way. If you lose the mount thru an errant recal or sync, a simple "Home" will re-establish the correct co-ordinates. This is the way we have set up our remote mounts in Chile, and they have NEVER gotten lost due to operator error, computer malfunction, internet crashes, power outages and other small disasters. They have operated remotely for over 6 years without a single issue. The reason is that we locked the clutches when we set them up so that they are basically the same as any clutchless mount. So, it doesn't matter how many times you unlock the lever and move the axes, or lose power or anything else, the mount always knows where it's pointed because it has absolute encoders. You don't even have to home it after moving the axes this way, the encoders track the movement - no homing needed, although it's always available.


For our non-encoder mounts, if you move the axes, you will not lose the PE correction. Our mounts will not lose position if the power is lost. Just turn power back on and resume from present position, or set the keypad to Autoconnect. If you leave the clutches locked in a permanent setup, you can also always send the mount "Home" via APCC if you make a mistaken recal or sync. So, again the poster's information is incorrect - our mounts do not lose PEC when the axes are moved. You will lose pointing in our non-encoder mounts if you unlock the clutches and move the axes manually, but that has always been the case, and you can quickly re-establish pointing by simply resuming from a known park position (you have 5 to choose from).


In our design of the 1100 mount we could have left off the upper portion clutch assembly and made a simpler clutchless mount. However, then you would have lost the ability to use the mount manually with the clutches set to slip. You would not be able to move a scope around in a sweep of the sky or Milky Way and have the mount track when you let go. You would also lose the ability to place the scope into a normal position in the cradle plate or at 90 degrees in a side-by-side multi-scope configuration without re-orienting the cradle plate.


The 1100 mount is NOT like other mounts, it has both clutches and worm gear unlocking. Unlike 10-micron, it has hollow axes into which you can stuff power, USB, Ethernet cables, etc. to your heart's content. You can order it with and without Absolute Encoders for true remote imaging applications, or just for the best way to do high resolution imaging. It comes apart for easy setup-tear down. You can hot plug any of the cables without fear of destroying the electronics. It has robust protection against severe static discharge and won't be damaged short of a direct lightning strike.


Roland Christen

Astro-Physics Inc.



Roland Christen

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