help needed with servo motor

Thread Starter

aliyesami

Joined Sep 12, 2009
11
I have never used a servo motor so please ignore anything stupid I ask.
I need to know if i can use a small dc servo motor to turn a lever from 0-135 deg and back to 0 ?

and what kind of drive signals are needed to step the motor at various angles ?

thanks
 

djsfantasi

Joined Apr 11, 2010
8,254
Yes, you can. Servos are driven with a PWM signal between 750-2250 Hz. 1500 is the center position. Google RC servo signals for details.

Actual positions are -90 to 90 degrees. Easily mapped to 0 to 180 degrees, which is inclusive of 0 to 135 degrees.
 

Thread Starter

aliyesami

Joined Sep 12, 2009
11
thanks for the quick reply , i have experience with PWM signals so driving Servos should be easy.
any servo motor you can recommend to interface with ardiuno ?
 

Thread Starter

aliyesami

Joined Sep 12, 2009
11
Yes, you can. Servos are driven with a PWM signal between 750-2250 Hz. 1500 is the center position. Google RC servo signals for details.

Actual positions are -90 to 90 degrees. Easily mapped to 0 to 180 degrees, which is inclusive of 0 to 135 degrees.
also wanted to ask , how fast the servo motor spindle moves ? I want a relative fast movement. , the PWM signal controls the angle so how do you conrol speed?
 

djsfantasi

Joined Apr 11, 2010
8,254
The speed is set by the parameters of the servo motor. You can drive it slower by stepping the angle and delaying between steps in software.

The Arduino natively supports hobby RC servos. There are sample sketches supplied with the IDE. The Arduino reference pages describe the servo library. You don’t directly write the PWM signal to the servo. You let the Arduino library do that.
 

MisterBill2

Joined Jan 23, 2018
11,556
OK, I am guesssing that it is not really an actual servo motor, but rather a Radio Control servo that must be used with a radio control receiver. That is a much different device.
 

SamR

Joined Mar 19, 2019
4,117
Yes, it is a hobby DC servo motor controlled by programming the uP in an Arduino. Usually comes with a bellcrank. Lot's of sources for them, Amazon, Alix, Digikey, and many others.
 

dendad

Joined Feb 20, 2016
4,109
but rather a Radio Control servo that must be used with a radio control receiver.
No, they do not need a radio control receiver,
Just any device that can produce a suitable pulse train to drive them.
The Arduino is ideal as they are cheap and there is heaps of info on line of how to do it.
 

Reloadron

Joined Jan 15, 2015
6,507
I have never used a servo motor so please ignore anything stupid I ask.
I need to know if i can use a small dc servo motor to turn a lever from 0-135 deg and back to 0 ?

and what kind of drive signals are needed to step the motor at various angles ?

thanks
Small hobby servo motors, like these as an example, use a PWM input as mentioned. The frequency should be at least 50 Hz because the servo motor wants a refresh rate about every 20 mSec, The pulse with will generally drive the motor 90 degrees left or right rotation and the pulse width is between 1.0 and 2.0 mSec. A pulse width of 1.5 mSec will place the rotor at center. They are easily driven by several means depending on exactly what you want.

Mentioned above and pretty important is choosing a servo which has enough torque to drive your load. Actually 0 to 135 degrees becomes -67.5 degrees to 67.5 degrees and yes, is very doable.
also wanted to ask , how fast the servo motor spindle moves ? I want a relative fast movement. , the PWM signal controls the angle so how do you conrol speed?
This would go better if your application in detail were known.

Ron
 

MisterBill2

Joined Jan 23, 2018
11,556
No, they do not need a radio control receiver,
Just any device that can produce a suitable pulse train to drive them.
The Arduino is ideal as they are cheap and there is heaps of info on line of how to do it.
OK, but for the first 20 years they were ony used with RC receivers, and that is the format of the control signal. a variable width pulse every few milliseconds.
 

djsfantasi

Joined Apr 11, 2010
8,254
OK, but for the first 20 years they were ony used with RC receivers, and that is the format of the control signal. a variable width pulse every few milliseconds.
Well, for the last twenty years, that hasn’t been true. In fact, analog control of hobbyist RC servos is on the way out. Current RC servos are digitally controlled now. So your experience is at least two generations old.
 

shortbus

Joined Sep 30, 2009
9,320
Well, for the last twenty years, that hasn’t been true. In fact, analog control of hobbyist RC servos is on the way out. Current RC servos are digitally controlled now. So your experience is at least two generations old.
You do know you're arguing with our newest "expert" don't you? He won't like that. :)
 

MisterBill2

Joined Jan 23, 2018
11,556
You do know you're arguing with our newest "expert" don't you? He won't like that. :)
That is how they worked back in 1985, when investigated how they worked. And isn't the digital scheme still a pulse with signal? That is certainly digital. And why am I being called an expert? I don't think that I said that.
 
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