Linear actuators

Hey all
I have just finished - or at least 80% finished my first 2dof rig with 2 nema 34 steppers and 20:1 gearbox. I’m experiencing some jogging / stepping movement and can see that this not an uncommon thing. Have tried a lot of stuff tweaking simtools and the arduino sketch, but can’t quite get rid of it.

A couple of questions:
- are there some “standard” arduino sketch you are using for motor control. I have made mine myself and are thinking that that might be the issue?
- I had tons of fun making it and seeking knowledge but are considering shifting from the rotational stepper actuators to linear actuators. How fast do the need to be and what torque / nm ? As far as I can tell this might fix the issue?
Best
Jacob

So far as far as I know there is no standard stepper motor sketch. There is not enough info in your post to understand what problem you are having.

The standard sketch is SMC3 which supports 3 servo gear motors at a 4khz update rate. Generally the servo motors are gear motors used with lever arms. For a rocker aka ujoint in the middle you need > 25Nm at the motor. That also depends on the length of levers arms etc. So that may involve a range of 50:1 to 30:1 and a top speed of 30-100 RPM.

As for a linear actuator there are lots of options. Look at https://opensfx.com/documentation/ for a good tried and true example of that kind of system. Most people here use AC servo motors for linear actuators. That can get expensive but not as expensive as it used to be maybe $150 per motor/amplifier.

you need scn5 or scn6 linear actuators really but theyre not cheap
let us know what problems youre have with the motors in more detail and should be easy to iron out

Instead of a fluid motion they sort of step a bit, making small movements that I can feel in the rig. Its not too bad, but I expected a smoother ride. If I test movement in Simtools its the same result, so I guess its either just the way the steppers behave or something in the code. The code is largely done with ai but without SMC3 - so I will look into that option.

I can send som pics of the rig when I get home if you guys promise not to trash it ;-)

Yeah send some please there are many janky builds here including my own
The issue is bound to be software related unless you have an unbalanced rig