Servo motors


Here is a total newbie question. I am getting totally confused with the jargon surrounding motors. 1)The RC servo community seems to refer to servos as devices that can maintain a particular angle, but not capable of continuous rotation. But i believe servos such as, are capable of continuous rotation. So what is a servo?? 2)If i want to maintain very precise rpm control(make rpm change as i wish for example like a sine wave), would i use a servo or a DC motor? 3)If i want to maintain a precise angle and change the angle as i desire, would i use a servo? 4)What is the difference between a motor drive and a motor controller? 5)Can i convert a DC/AC motor to a servo using feedback control with pwm signals generated by the Arduino and a suitable motor controller and encoder. 3)Can i control the above Beckhoff servo using an Arduino? Do i need to buy the Drive from them?

Sorry for all the basic questions, but i can't seem to find an answer anywhere. The sales-reps just confuse me with more terminology.

Thanks Sam

Thanks, that clears up quite a few issues.

This is what i want to do 1)Build a disk whose rpm varies smoothly(like a sine-wave). It could be shifted by a DC value if the motor can't rotate in the reverse direction. 2)Place the Ardu-imu on this disk and log the rotation angle as measured by the encoder and as measured by the imu.

This way i will know how accurate the Ardu-imu is. I don't need high rpm's. 60 would probably be the peak rpm. To do this should i buy a "servo" motor like Beckhoff or a plain vanilla DC motor and try to control it's speed using pwm's from the Arduino and a motor controller?

Regds Sam

60 would probably be the peak rpm

If you could go as low as 45, an old-fashioned record deck could be a cheap alternative. (A really old one could do 33, 45 and 78!)


@KE7GKP Why do you say, that the test system has lower reliability than the Ardu-IMU? Shouldn't the accuracy of the test system be determined by the least count of the encoder? I want to also modify some of the code on the IMU and check the results, to see if it gives a more accurate result. Won't a stepper motor have backlash error?

@AWOL Unfortunately i threw away my record player about 3 yrs ago. So how do i achieve such low rpm's

Thanks Sam

Your description of the test method seems open-loop. There was no explanation of how to correlate the Ardu-IMU data with the turntable position / speed / orientation. For that matter, how do you even know the instantaneous information about the turntable? And how do you get the data from a spinning Ardu-IMU?

Sorry for not being clearer. I have an Xbee shield that will sit on the Ardu-imu on the rotating disk, that will act as the transmitter. Another Arduino will sit on the ground with an Xbee shield(reciever) and a Datalogger shield. This stationary Arduino will log the encoder signal and the Ardu-imu data with time-stamps. This way i will have correlation between rpm of the rotating disk and the imu data. Therefore as long as my encoder is accurate, i can treat it as a benchmark to evaluate the imu.

Thanks Sam

Just a minor correction: A motor drive is a electronic system that controls the speed and direction of a motor (as well as numerous other things)

I assume that a motor controller is the exact same thing, just a different term for it.