lelef wrote: ... but my x axis isn't very fast and powerfull with a stepper so I will change it with a better sized dc servo
Sounds to me like your stepper is either grossly undersized or grossly underpowered, or both. A properly sized stepper that is properly powered could easily make the moves shown in those videos. I have a nema 23 stepper system running 500 inches per minute without fear of stalling (on a cast iron dovetail slide), and 500 ipm is faster than anything in those videos, and it was not expensive--just chosen with care.
One of the bigger expenses to a great stepper system is the power supply, so instead of spending $200, people often spend a fraction of that, and get a cheapass $30 power supply and expect "almost as good" performance, because "afterall, the motor is only rated for 5v." Then they end up with a crummy system, and blame it on the steppers rather than a poorly chosen system. There is a huge difference in performance between a 40v and 70v power supply...it is the difference between mediocrity and possibly outperforming a cheap servo system. (Obviously, the definition of "outperform" depends on the system goals.)
You pinch pennies on your power supply, and you will be wondering why your so-called 300oz-in stepper stalls at 50 inches/minute, and you will be thinking you need a 1,000 oz-in servo to get the speed you want, but in reality all you needed was an adequate power supply. The big difference between steppers and servos is the mindset. Servo drives are not considered "cheap" systems, so shoppers don't have the penny pinching mindset and the resulting systems are less likely to be underpowered with a crummy power supply.
