This is a follow-up to my earlier post about putting together a home-built Arduino-controlled stepper-based absolute focus controller. As our last episode closed, I had determined (with the help of Robert Brown, the developer of the
MyFocuser Pro system) that my original DRV8825 motor controller and LCD board were both bad, and was waiting for replacements to arrive on the slow boat from China. Both came shortly thereafter, so I unsoldered the bad DRV8825 and replaced it with a good one, and voila! The stepper motor began moving the way it was supposed to. Wiring on the new LCD produced a similar result: the new one works great.
Next I had to put together a bracket to mount the stepper motor on my focuser via a flexible shaft coupler. I don’t really have the right tools for the job, so this was messy, but with a power drill and a file I slopped something together that works.
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| Stepper motor mounted on focuser via flexible shaft coupler |
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| Control box for the focuser. "In" and "out" buttons are on the front, and power and programming switches are on top. The USB connector is on the bottom, and the temperature sensor and power both plug in on the right. The connector for the stepper motor is the D-sub connector on the left of the image. |
I followed Robert Brown’s instructions to install the Windows control software and the ASCOM driver, and for calibrating the motor control. The focus motor performs quite well and positioning looks to be very reproducible. Unfortunately, the focusing algorithm in Sequence Generator Pro 2.5.0.23 wasn't up to the task for automatic focusing, but I learned this is a known issue (problems with scopes that have a central obstruction, like my Newtonian) that has been addressed in the 2.5.1 beta, so I downloaded that. The focus motor and the Sequence Generator Pro 2.5.1.10 focusing algorithm both worked very well, so I’m now able to perform temperature-compensated automatic focusing throughout a run. I also added a cheap gamepad controlled through EQMOD to move my mount around without having to carry my laptop out to my scope (complete instructions for doing this are on the EQMOD web site). That makes lining up on a sync star really easy.
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| Gamepad for mount control. |
Finally, I put my old Orion Accufocus DC focus motor controlled through a Shoestring FCUSB on my ST-80 guide scope, so now I can remotely focus both the ST-80 and the AT8IN. The total cost for everything for the new focus motor and controller was less than $100 even after my fumbling around and less-than-fully-efficient purchasing, a lot less expensive than the cheapest commercial system I could find (more than $400), so I’m really happy with how all this turned out. If I were to do it again, I probably would not have bothered with putting manual pushbutton controls on the focuser box nor with the LCD. I use the computer to control the focuser and never use either the manual buttons or the LCD display (but the display does look cool, and didn’t cost very much).
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| First use of MyFocuser Pro. |
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| An autofocused image using MyFocuser Pro to update focus during the run. |
