Converting a 12″ Dobsonian to OnStep

I have been bitten by the astronomy bug and quickly learned to love two things: aperture and GoTo telescopes. My first experience with a computerized GoTo scope came from a Celestron NexStar 6SE, which is a very nice scope and will open up a TON of viewing for many people. The GoTo feature is wonderful for those of us that have less than ideal viewing conditions such as light pollution.

I also had a chance to look through a friend’s 12″ Dobsonian telescope, a Zhumell Z12, and was amazed by how much brighter the views were. I quickly found myself wanting one of these wonderful scopes as well, but couldn’t find myself paying for a full goto 12″ or 14″ scope like the Skywatcher 300. As of February 2022 when I started this journey, a scope like this would cost around $2500 with full computer control. If you choose to go the Cassegrain approach, a new Celestron CPC1100 will cost ~$4000 at today’s pricing.

I ended up purchasing a 12″ Zhumell Z12 of my own, and decided to convert it to a computer controlled GoTo Scope myself. Given that a new Zhumell Z12 goes for ~$1300, that leaves about $1200 to break-even on a control system. I’m estimating I can get similar features in a $400 budget, which should be a nice savings. Especially considering that I’ll probably copy that system over to my friend’s Z12 as well.

I decided to use the OnStep software to control it because it looks like there is a robust user community supporting this, and it will give me the long-term ability to upgrade/repair any electronic failures without being held hostage by a shortage of parts from Orion or Celestron.

I’m going to have this as a primary post to document the process of the build, and hopefully link to the steps along the way. I’ll start with a list of my questions, and answer each one in a post to give more documentation.

How to select the motors/drivers to use for this?

Learning to Program the Controller

How to mechanically adapt to the telescope? Many files will be uploaded to:

AZ Motor Mount Bracket

AZ motor Mount and Wheel

100 Tooth Gear for Alt Axis

How much will this cost?

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