Well, as I’ve mentioned, the tracker did not quite have enough torque for my heavy ball mount and camera with my 18-200mm lens. It worked fine with my micro 40mm lens.
So the designer’s suggestion was to try a finer pitch lead screw. That may have done the trick.
Originally I had used a 2mm pitch, 4 start, 8mm lead, lead screw — confusing parameters, but for sure that screw advances 8mm per revolution. Now I bought a 2mm pitch, 2 start, 4mm lead. and that does advance 4mm per revolution.
The idea is if it takes twice as many revolutions to advance the same distance that it should support a heavier weight for the ball mount/camera/lens combination.
And indoor tests with the camera with lens on, in the most challenging orientation say that it is advancing about .25 degrees a minute.
Now, since the threading is different, the nuts are different between the two screws, so you can’t just thread in the new rod. Since I had to buy a set of 5 stepper motors, I opted to not try to take apart the original motor mount, but to just print and assemble a new one. A couple things came up. First the mounting holes in the new nut are smaller, and so the nut did not fit on the gear with the peg. So I had to print the peg-less version. Also the hole in the drive screw head seemed a bit too small. Rather than print one with the hole enlarged, I just tightened it on as best I could.
Also a software change needed to be made. The screw has to advance faster so if you look at the formula:step_tgt = 1.56365E5 * sin(8.809E-2 + 3.646E-8 * millis()) - 13756.5;
Two terms need to be twice as much:
step_tgt = 1.56365E5*2 * sin(8.809E-2 + 3.646E-8 * millis()) - 13756.5*2;
The proof that it works will be to go out and track a star. Like see if I can get a one minute exposure. Oh, but this is the North East and stars don’t shine through clouds much.
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