servo motor control.........

[mathus]

hii.......
i am trying to rotate a servo motor using 8051mc.
i can rotate it using pwm (high-delay-low)clockwise...but when i am trying (low -delay-high) my servo is also moving clockwise..can any body help me or to any other method to do anticlockwise......

 

[Jestin_cubetech]

------------------->| |<------ 1ms - 2 ms
_...........................__
|_______________| |___________
|<------ 20ms ----->|


1.5 ms = 0 deg
1.0 ms = -90 deg
2.0 ms = 90 deg

 

[mathus]

thanks jestin can u explain me a little bit more........

 

[ivlsi]

What is SERVO?

 

[js]

@jestin_ .... only "say" that servo isn't controled with pwm!
read this:
**broken link removed**

 

[jpanhalt]

@jestin_ .... only "say" that servo isn't controled with pwm!
read this:
**broken link removed**

Servos are controlled with pulse width, not duty cycle. Another way to restate post #2 is that 1.5 mS is center. Any pulse width less than 1.5 mS but more than 1 mS moves it CCW (anti-clockwise) and pulses greater than 1.5 mS and less than 2 mS move it CW (clockwise).

Those are just general guidelines. Servos can be reversed and some can even be bought that way. Older servos used a different value for the center position, and servos can often be driven outside that range, e.g, 120% of full throw.

The other factor to consider is the repeat rate for the signal pulse. It is standard to repeat it at 50 Hz (i.e., 20 mS between pulses), but servos are quite tolerant of faster and slower repeat rates. When driving with a microcontroller using the hardware PWM, the problem is usually too fast a repeat rate. Analog servos will work up to about 80 to 120 Hz (brands vary). Digital servos are said to work to about 300 Hz, but I have never tested that myself. The other problem with hardware PWM for driving a servo is poor resolution (it is relatively easy to calculate from the datasheets).

However, from your (mathus) description, it appears you are doing software. Clearly, delay > pulse and pulse > delay will give the same result, if the pulse width is the same.

John