Hi,

I missed this, but there is a misconception about micro stepping.

Microstepping will not improve accuracy as you have seen. You should do all your calculation on the distance a full step moves an axis. At a pinch you could use the 1/2 step distance.

The reason is that with microstepping, the driver is attempting to hold the rotor between the full step detent position, by adjusting the current in the two windings, using the sine and cosine of the required angle.

A number of things work against this method from being accurate.
  • The first is the the two windings in the stepper are not absolutely identical, therefore, even with the winding currents being correct, the resulting rotor will be off a bit and not linear across the range of micro steps.
  • The detent force of the motor is trying to pull the rotor towards it. This is stronger the closer the rotor is to the full step position.
  • The forces of the axis pushing against the motor pushes the rotor from it's theoretical position.


Some of what you have seen is explained by the above. There is no movement on the 1st microstep as the force is not enough to overcome the detent force and the axis resistance. As the microsteps increase the rotor springs into position.

Microstepping was introduced to provide a smoother movement motion at low speeds, rather than cogging from one fullstep position to another.

If you need greater accuracy go to a 0.9 degree stepper than than 1.8 degree stepper, or gear down the drive.

BTW, great video.

Cheers,

Peter


Quote Originally Posted by flippersplace View Post
Hi Roman, when planning this machine with a T5 5mm pitch belt, I decided on 16 tooth pulleys which with 1.8 deg stepper = 2.5 steps per mm, which if I then microstepped at 1/16 came to a nice round 40 steps per mm which equals the mil units I'm used to. (Actually I'd be happy with a reliable 20 steps per mm)

In my initial testing once the gantry was in motion, with microstepping at 1/16 (experimenting) I wasn't getting consistant movement when single stepping. It was like every 8th step or so was showing no movement then it would catch up on the next. So because I needed a bigger stepper for the X anyway I figured I'd go for the 0.9 degree ones. and see if a higher physical resolution hence less reliance on microstepping would help.

Not very scientific but I am curious to see what the 0.9 deg steppers go like. I had no idea what the belts would be like / will perform like set up this way so its all a bit of a fun experiment..