On 08/11/2011 08:28 AM, Mark Wendt wrote: > I knew about the properties of the torque fall-off of steppers, and > that servos generally kept their torque at higher rpms, obviously much > better than steppers. i was just wondering why motors were listed with > power ratings rather than torque, since torque is more along the lines > with how we determine what we need from a driven motor than power. Must > be like you said, HP, especially in motor vehicles seems to be a selling > point, kinda like "billet" aftermarket auto parts. To me, anyway, I > would much rather have the torque ratings up front, and in an industrial > environment, where somebody is going to use that product to drive a > machining operation, I would think the integrator would much rather look > at what really needs to be looked at, not the eyewash. I believe it's all necessary. The power level is to let you know how hard you can drive the motor without letting out the magic smoke. It doesn't translate well into torque or RPM mathematically because efficiency of the motor can make that swing wildly, and a 90 percent efficient motor designed for speed will have much lower torque at rated power than a 90 percent efficient motor designed for torque. You can't equate current with torque either, since two of the same motor core and magnets; one wound 10 turns of thick wire, and the other wound with 20 turns of a thinner wire will produce different torques at the same current.
The power rating is probably there to let you know that if you push it beyond that for any length of time, and let out the magic smoke, they won't just replace the motor for you every week. With a servo motor you usually have a max current rating, and a max voltage rating. The supply is usually chosen so that max power supply voltage times max motor current will be many times the motor max power because the spinning rotor develops back EMF (Electro Motive Force, or voltage). You need the higher voltage to push current in when the back EMF gets high due to high speed operation, such as going to and from the tool holder. That same voltage is enough to supply too much current when you are trying to push a 2" shell mill through stainless steel, or cut away a large chunk of aluminum. Our Shizuoka has about 90V available for the servo motors, and probably needs all of that to push a few amps at 3000RPM (due to back EMF canceling out much of the voltage), but in a stall, it needs much less voltage to push up against the 10 AMP current limit. ------------------------------------------------------------------------------ Get a FREE DOWNLOAD! and learn more about uberSVN rich system, user administration capabilities and model configuration. Take the hassle out of deploying and managing Subversion and the tools developers use with it. http://p.sf.net/sfu/wandisco-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
