Le 09.07.2014 23:09, Przemek Klosowski a écrit : > On Wed, Jul 9, 2014 at 12:23 PM, Claude Froidevaux <men...@bluewin.ch> > wrote: > >> to get en estimate of needed voltage: >> >> get the speed you need in rad/s (1t/s --> 6.28 rad/s) >> multiply by the torque in Nm >> >> this will give you the output power of motor at max speed. >> >> then, as you know the current inside the motor, you can deduce minimal >> needed voltage to get the same power (plus additional waste) >> >> for example: >> >> stepper: >> 4Nm, 4.2A >> >> need 1000rpm (5 m/min with 5mm leadscrew) >> >> power @ max speed and max torque: 1000/60*2*pi * 4 = 104 W >> >> P = U *I --> 104 / 4.2 = 25 --> we need at least 25V, but this is >> without taking any loss in accout (resistance, drive, sinus factor, >> ...). Doubling this value will get you something that shall do the >> tricks! (so 50V needed at least) >> >> this is a really rough calculation, but it help a lot to know what is >> needed. >> > Sorry if I am making a simple mistake (I plead lack of sleep today) but > isn't 4 * 2 pi 1000/60 equal to 419? More importantly, as you indicate that > formula is flawed, because usually the max torque requirement is usually > at low speeds, when you accelerate the axis. Of course the stepper motors > lose torque at max speed, so the above formula is just a ballpark estimate; > true V estimate should take into account the motor's Back-EMF (kV) > characteristics, I believe. >
You are right, I missed my calculation (sorry). Be careful that acceleration is usually the same up to top speed (standard trapezoidal or jerked move), but often you can accept less torque at high speed than low speed (assuming not everything is used only for acceleration). Of course the right way is through back-EMF, but stepper motor almost never give this value (you can know it with a drill machine an some equipment, but this assume you already own the steppers). This tricks give the ability to coarse estimate what you can get, or what you do need. What is really important is that you still get some current at max speed (lets assume 1A only, if voltage is not enough, you will reach state that current go to zero, and motor stall. (you can also simply measure current on delivered by power supply, it shall still provide substantial current (let say at least 25% of rest current) when reaching maximum speed. ------------------------------------------------------------------------------ Open source business process management suite built on Java and Eclipse Turn processes into business applications with Bonita BPM Community Edition Quickly connect people, data, and systems into organized workflows Winner of BOSSIE, CODIE, OW2 and Gartner awards http://p.sf.net/sfu/Bonitasoft _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
