is it possible to make the servo motor move precise angles besides 90,0 and 180 by using pwm signal width in between the waveforms of full right/left and the neutral position?

 

servo has 150-75 = 75 different positions to be. you dont have to send it 150 or 75 you can also send 127.

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A servo is an analogue device, it can be set to anywhere within it's operating range (and it usually goes a little way outside it's range as well).

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Hi,
A normal servo has a 1-2ms pulse interval repeated every 20ms(more or less.)

The midpoint is at 1.5 ms.

If you make use of a microcontroller and its timer to generate a clock pulse every 4 us, you could make a counter with 255 divisions / steps between 1 and 2 ms. This would give you complete control of the position of the servo. In fact it's more than complete because the servo does not recognise all steps due to the mechanical lag.

127 pulses is more than enough, so if you increase the input clock period to 8 us, you could use a value from 128 to 255 for the variable pulse. This is about 1 to 2 ms pulse width interval. This is then repeated every 20 ms.

Hope I made some sense

TOK

 

Trying to make it a little more clear, like they said, it's an analogue device. Theoreticly you can have inifinite number of steps between far laft turn and far right turn. The resolution is limited by the mechanical servo itself, and most hobby servos, there's no real point going beyond 127 step resolution.

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Mark Higgins

 

nigel, is your tutorial "Using the PWM hardware" meant to be a tutorial for controlling a servomotor?

 

hehe, its because I need to control the precise angle of the servo for tracking an object with 2 cameras and the application requires very precise angles to be able to compute the exact distance of the object

 

No, the PWM hardware isn't really suitable for that, the tutorial is for speed control of a simple two motor robot.

I would be inclined to test the resolution of your servos if you need precise control?, there are plenty of servo tester designs around using one or two 555's.

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Then the quality of the model servos will be a factor in how precise you can control them and how accurate you can assume the angle is that you've set. You can get some very good results from digital servos (same as regular hobby servos, they just have better control built in)

Hobby servos have their own control electronics. If you want the most accurate you can pull out the electronic guts of the hobby servo and create your own controller. This would give you better control, and actual feedback regarding current positioning by reading the pot directly.

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Mark Higgins

 

what is the best and cheapest choice of microcontrollers to use if I have 4 servos to control by interfacing the PIC to a pc?do you know any good tutorial about the microcontrollers?

 

Your search starts here : http://www.electro-tech-online.com/viewforum.php?f=11

And continues there : http://www.piclist.com

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