After the initial excitement of researching mounts and optical tubes and all things telescopes I decided that I should just buy something off the shelf.....

That lasted for about five minutes before I started researching specs and working out what it would take to build something. I spent a little time contemplating between and ALT/AZ or a EQ mount but given that I wanted to use the mount for ground based targets as well as astronomical I pretty quickly decided on ALT/AZ.

The speeds and accuracy of something like the Planewave I-350 seemed to be a good target and I started doing the maths to see what combination of gears, belts and motors would give me good tracking speeds whilst also allowing small enough step sizes that I could try my hand at some long exposure astronomical photography.

I decided to buy the biggest stepper motors I could reliably fit into a mount and then microstep them as far as possible to get the minimum step size down. My final drive train would look something like a Nema 34 motor @ 12nm with microstepping set @ 40,000 steps per rotation. I based my calculations on a 30t gear on the stepper and a 160t gear on the output for a minimum step size of 0.0016875° or 6.075 arcseconds.

The Planewave has a minimum step size of roughly 0.07 arcseconds, so I'm along way off that but I can still add in a reduction gearbox if needed. I double checked a few other numbers such as expected RPM and with control signals at 200 kHz I could expect 56 RPM on the final stage which was more than quick enough.

So in went the order for two closed loop Nema 34 kits to start basing the build on.