Re: STM32 - OnStep


Howard Dutton
 

I've been in this group for quite some time. I have successfully carried out the transformation of the dual axis motor kit (eq3,2,5) to Goto through nanoarduino and its autoguiding system with good results. I've been wanting to go a step further for a long time, replacing those engines with Nema17s and jumping to Onstep. For one thing or another I have been postponing this jump. Already decided, I have chosen, because in my country all its components are obtained, in the STM32 model. As I am the founder of an astronomy group in Argentina, there will be about 5 of us so far that we will transform our EQ3, 5, Dobson equipment, into Onstep using the detailed model (STM32). Of course, doubts arise in this regard and more than in our country, the components, parts or accessories of an astronomical and electronic equipment have very high costs. One of them is the use of the DVR8825 and LV8729 controllers. The cost difference is important. I have read that the LV8729 is very good, quiet and other data that is of relevance. The concise question is, what are the disadvantages in using the DVR8825, understanding that the equipment will be used for Astrophotography. I am sure there will be more concerns but I will bring them up in due course.
The issue with the DRV8825 is with the accuracy of microsteps, this is a known issue in the 3D printer community as well as here.  The DRV8825 can be ok (not great) with some stepper motors, it's hit 'n miss.

This article shows what you can expect from an DRV8825 when it's not working well (which is often:)
https://hackaday.com/2016/08/29/how-accurate-is-microstepping-really/

A nice write up of the issue, which covers two ways to "fix" it, is here:
http://cabristor.blogspot.com/2015/02/drv8825-missing-steps.html

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