255 steps for a servo?

Status
Not open for further replies.
G

gastonanthony

New Member
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.
 
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).
 
gastonanthony said:
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?
Click to expand...

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.
 
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
 
gastonanthony said:
nigel, is your tutorial "Using the PWM hardware" meant to be a tutorial for controlling a servomotor?
Click to expand...

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.
 
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.
 
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?
 
servomotor circuit


i need a circuit of servomotor capable of producing mechanical displacement can u plz suggest me any link or book or ur approach towards it would be great
 
gaston you have to more precisly define "precise angle" Hobby servo's aren't really meant for very high repeatability and the mechnical setup is going to be more important than the electrical one, exactly what kind of precision and repeatability do you need?
 
Yep, once you put a bit of load on a RC servo it's repeatability drops to +/- a few degrees.

I would use stepper motors and a microstepping stepper driver. If you try a Linistepper;
**broken link removed**
it contains a PIC chip and oipen-source code, and the PIC chip generates averaged software PWM signals.

It's the only stepper driver on the market that can do absolute position control, meaning that you can program the PIC to produce any PWM values, to turn the stepper to any angular position you want. They are popular with the astronomy guys that use that feature to position their telescopes using stepper motors so the telescope synchronises to the slow rotation of the heavens to do time lapse photography.

That will get you to the repeatability of the stepper motor itself which with a good stepper should be very high.
 
This thread is 4 years old. I think Gaston has even left the forum.

Mike.
 
Status
Not open for further replies.

Similar threads

C
  • Question
am my steps about my question solution about bjt correct?
Replies
9
Views
3K
MrAl
M
O
  • Question
Help finding a replacement relay for sealer
Replies
12
Views
2K
Diver300
D
F
  • Question
Y capacitor location for Conducted immunity?...for conducted EMC?
Replies
0
Views
568
Flyback
F
  • Question
Help selecting a 1A BJT for 200KHz switching?
2 3
Replies
45
Views
7K
Roff
J
  • Question
Removing gel pot for lamp body repair
Replies
10
Views
609
rjenkinsgb
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…