I'm new to the world of 3D printing, so I'm trying to figure some of this stuff out. As I understand it, the range of speeds that the printer head moves is generally between 30 mm/s (for more accurate stuff) and 100 mm/s (for super rough stuff). However, when I look at the torque curve for the OpenBuilds Nema 17 stepper motor, it looks like the slowest speed is ~500 pps and highest speed is ~8000 pps. Putting a 14-tooth pulley on this and converting PPS to mm/s, I believe that works out to about 70 mm/s and 1120 mm/s respectively, if my math is right.[1] So, how does one move the head at 30 mm/s if the motor will go a minimum of 70 mm/s with a relatively small pulley? Does the speed of the motor actually go to zero and that is just missing from the torque curve? If so, it seems like the gearing the motor down (i.e., to make the max speed 100 mm/s) would be advantageous. Maybe I'm missing something though. [1] 500 pps * 1.8 deg/step / 360 deg/rev * 14 teeth/rev * 2 mm/tooth = 70 mm/s 8000 pps * 1.8 deg/step / 360 deg/rev * 14 teeth/rev * 2 mm/tooth = 1120 mm/s
Typically you wouldn't be using 1/2 step as in the graph - more like 1/16th or 1/32nd, so that changes the torque curve view itself quite a bit That graph merely indicates the expected tapering off of torque as a function of rpm, which is standard for all stepper motors - the measured torque, over the speed produced by sending certain pps (rpms) to it - it does not indicate upper or lower limits of achievable RPM The actual usable speed range is somewhere between 100mm/min and 10000mm/min for our typical configurations (note mm per Minute) depending on torque requirements of course (hotend weight etc) Highest and lowest used by the manufacturer during the torque measurement test - not a limit on what it can do, just what they used
