CNC machine

skylight

I've been contemplating getting one of those cheap ebay ones and changing the control board for a decent one like here:

http://www.planet-cnc.com/index.php?page=home

One thing that has occurred to me is the speed of change of direction along the axis or the spindle.

with rapid changes how come the motors don't blow the fuses or do the controllers disconnect the motors for a few milliseconds to slow down the motors and allow change of direction without huge current draw?

Or are steppers not prone to drawing heavy current when direction is changed rapidly?

JasonDorie

Typically the control software (like Mach3) is configured with acceleration curves, so the motors never change direction instantly. Larger CNC machines can have significant mass, and can move fairly quickly. My gantry probably weighs at least 40 lbs, and moves over a foot per second at top speed. Instantly reversing that would put some serious mechanical stress on the whole machine, not just the motors.

Stepper drivers are also generally set up to pull the same current all the time. Some drivers will reduce it when the motors are "at rest", but that's usually optional.

Erik Friesen

One disadvantage to this setup is that you are married to their software. Personally, I use linuxcnc with a mesa 7i25 parallel card, and probotix breakout. I looked at that software, but when I checked it lacks some features linuxcnc has, like rotating the work area. Its probably easier to use out of the box, perhaps.

Mickster

Not quite as it appears. In reality, each motor is moving according to an incremental command where the motors move and stop but at a rate where the motion appears to be continuous.

Mickster.