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What's the best motor used for position control?

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powersys

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What is the best motor used for position control? Do you think this question make sense? Thanks.
 

mtkee2003

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yes
the best motor for position control is a stepper motor that has more poles.
because if a stepper motor has more poles can control less degrees.
 

samcheetah

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there are two types of position control; absolute positioning and relative positioning. the stepper motor uses relative positioning. you give the stepper a sequence of steps to move its rotor. at any time you know how many steps you are from some reference. the problem with such a system is establishing the reference and depending on the load the stepper might miss some steps so there might be a situation when you wont know where you actually are.

RC servos use absolute positioning. you always know where you are at any time. RC servos have lots of torque so there is no problem of missing steps as in steppers.

i hope that helps
 

powersys

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Do u think DC motor can be used for accurate position control?
 

samcheetah

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an RC servo is infact a DC motor fitted with a gearbox and some control electronics. the control electronics makes it a servo and constricts its movement to 180 degrees. if you take the control electronics out, all you are left is a DC motor and a gearbox in a cute little rectangular box. search on google for RC servos for more info

if you start with a DC motor you will have to make your own gearbox and some sort of feedback mechanism that will tell you the position of the rotor. if you dont know this stuff its going to be a messy job. i would recommend you an RC servo
 

powersys

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Do you think DC brushed motor or AC PM brushless motor, if configured as servo motor, will give better performance in positioning control? Thanks.
 

samcheetah

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the RC servo has a normal DC brushed motor. i cant say anything about and AC PM brushless motor configured as a servo motor.

an RC servo is a very easy to use motor and the best part is that its available off-the-shelf. you dont need to design the gearing mechanism, select the proper gear ratios, design some sort of feedback mechanism or build a control circuit. all you have to do is take the three wires coming out of the RC servo, connect one to 5V, one to ground and send pulses on the third. simple!!!!!!!

if you want to design your own servo mechanism then im sorry i dont know much about that.
 

xxargs

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samcheetah said:
there are two types of position control; absolute positioning and relative positioning. the stepper motor uses relative positioning. you give the stepper a sequence of steps to move its rotor. at any time you know how many steps you are from some reference. the problem with such a system is establishing the reference and depending on the load the stepper might miss some steps so there might be a situation when you wont know where you actually are.

RC servos use absolute positioning. you always know where you are at any time. RC servos have lots of torque so there is no problem of missing steps as in steppers.

i hope that helps


But if look inside ink jet printer, most (all) manufactures going from stepper motor to servo motor with feedback via zebra line/wheel. HP have always use servomotor from pen-plot time to now, but other manufactory (epson, lexmark) have often very loud and beeping stepper motor solution, but now for high resolution printning needs using servo depend of not can make fine step enough and soft moving in stepp motors compare to dot-distance without patterns in picture - and servo make printer bit more silence...

Is also long time ago harddrives going from stepper motors to voice-coil with servo loop, not only depend of wanted higher maximum speed...

In most case have motors with servo loop much higher resolution and faster response, but also more complicated to design (special for digital and programming people with no 'analog' experience) and needs analyze whole mechanical system to make best possible PID-paramters mm. depend of wanted respons.

(i make coarse calculate for long time ago on servo loop for focusing lens in optical pickup in 8x CD-burner, and find out needs bandwidth around 8 - 10 kHz to follow uneven surface still in focus in full speed, ie lens can vibrate as discant tweeter in loudspeaker, and this loop is pretty hard to make cheap in software, A/D and big crunching DSP, but cheap with OP-amp, couple of resistors and capacitances in analog way _if_ you find out right parameters on whole mechanical system...)
 

powersys

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Which motor, e.g. stepper motor, dc brushed motor, ac pm brushless motor, etc. is the best choice for high performance (especially positioning control) servo system?

Thanks.
 

samcheetah

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xxargs i agree with you. thats why i recommended powersys to use an RC servo instead of a stepper motor.
 

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