Here is a paper that describes how to find the sensor configuration for a=20 motor: /Ruben > Hi Denny, >=20 > The manufacturer should provide a commutation table - sadly, they > often do not provide them, but it is definitely worth asking for one. > If they don't know the commutation table, ask them for a particular > drive that is compatible with this motor and then look at the > datasheet for that drive. >=20 > You can determine the table by the method that you describe, but the > result is not as simple as "apply phase combination X, record Hall > output Y, and then whenever you see hall combination Y, apply X to the > phases". This is because the goal of commutation is to achieve the > minimum torque ripple and the maximum torque amplitude. If you lock > the rotor by applying DC to a phase pair (winding), you have > positioned the rotor at one of the zero torque positions for that > particular phase pair. The hall to phase voltage mapping has to > provide max torque, not zero torque, so for each given hall sensor > output, you need to drive the phases in the combination which causes > max torque for that rotor position, not zero torque. >=20 > For most BLDC motors, the hall signals (call them A, B, and C) will > each be in phase with the voltage between one pair of motor leads. If > you can spin the motor externally while using a scope to look at both > hall signals and back-EMF waveform, then you should be able to > re-construct the commutation table. Your commutation should apply > voltage which is in-phase with the back-EMF voltage. >=20 > I know I am not being all that clear here on the exact procedure but > that's because it is difficult to explain without showing someone in a > hands-on way and I don't have time at the moment to write out a whole > procedure here for you :) >=20 > Some motors will have a phase offset between hall signals and the > phase pairs but those type of motors will usually be ones that are > designed to run in one direction only and at high speed, like hobby > brushless motors for airplanes. The motivation here is that the phase > shift in the winding current versus winding voltage due to inductance > becomes significant at higher speeds and so the optimum commutation > switch points change with speed. Servomotors like the one you are > using operate at a wide range of speed and direction and so therefore > cannot simply shift their hall sensors to optimize for one particular > speed but rather they optimize around zero speed which gives good > overall performance. Hobby motors optimize for the speed range where > they will be generating the most output power and operating most > frequently. >=20 > Sean =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D Ruben J=F6nsson AB Liros Electronic Box 9124, 200 39 Malm=F6, Sweden TEL INT +46 40142078 FAX INT +46 40947388 ruben@pp.sbbs.se =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .