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Texas Two Step: Replacement dual-axis motor controller for Synta EQ3/EQ5 type GEMs

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#1 αLyraen



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Posted 13 January 2021 - 09:42 PM

A few years ago I had a thought that a joystick would be an interesting way to control a telescope mount, and put together a breadboard prototype of a GEM motor controller that accepted joystick input. It worked fine, and did what I wanted, but the breadboard wires were way too easy to knock out of place and eventually I got tired of fixing it every time a connection came loose. More recently, I had some custom PCBs made up so I could build a more robust prototype, and I’ve been pretty pleased with it so far.


I call the controller the “Texas Two Step”, with “Two Step” being a reference to the dual steeper motors, and “Texas” being a reference to the Texas Instruments motor driver chips and also to the fact that I designed and built it in Austin, Texas. The hardware design is open source and I have a GitHub project page for it here which describes some of the design goals that differentiate it from the stock OEM controller that comes with the Synta motor kit:




I’ve recorded a demo video of the most recent prototype which can be viewed here:




I have enough parts (I bought extra in case I broke anything) to make a couple more of these and can build them up if there is interest. My guess is that it wouldn’t be too compelling for most, since it’s not a complete solution, in that it doesn’t come with motors, transfer gears, and brackets, and you’ll need to already own the motor kit which comes with its own controller. It’s definitely an upgrade over the stock controller in many ways, but the Synta mounts are pretty inexpensive equipment and I don’t know how many people would want to invest a lot of money upgrading them.


If it looks like there’s more interest than a handful of people, I can look into setting up a production run to take advantage of better volume pricing for the components. Right now it costs me about $40 in materials for each unit, not including an enclosure. I think I will probably 3D-print an enclosure eventually, with a groove for mounting it on the counterweight shaft, with the possibility of getting it injection molded if there’s interest in a big enough production run.


Anyway, just wanted to share my little project and see if others might be interested. Let me know what you think.

#2 terrypaula


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Posted 13 January 2021 - 11:07 PM

Looks pretty cool. I bought something like it from AstroGadget to use on a CG4 and it works excellently.  But you have the satisfaction of building it yourself.

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