I have read a lot about servos and steppers. I have a mill that I have retrofit with servos and it runs great. When I had trouble with the servo drives ( I screwed them up ) I called Mariss at Gecko, he asked why I had picked servos over steppers. I thought it would be an easy answer but it isn't. If you look at the torque curve on each of them you will see that a servos torque is an upward ramp, the lower the rpm the less the torque. This would mean that the slower you move your table the less torque you have, this means you must gear down the motor to screw or use a lot larger servos. I ended up gearing mine on my mill to a ratio of like 4 to 1. The stepper on the other hand has its torque holding up to a given rpm then it drops off. If you keep your motor inside this rpm range then torque is somewhat constant to the table.
Open loop only with steppers? Not really, if you search here on cnczone for closed+loop+stepper you will run across some really interesting reading about EMC2 operating closed loop with steppers. I believe that there was an increase in the amount of power you could utilize from the motor when it was used with an encoder because there was less need to "overkill" when picking a motor/drive combination.
Noise? depends on the machine... on a router I can't hear much with the router motor itself on. The only time it becomes an inconvenience is when jogging without the router running. Vacuums are loud as well, all of these will cover any sound that a stepper might be making.
Danny  |