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Speed control of this circuit

bigkim100

Apr 17, 2013
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I found this circuit on Pinterest, and most of those are usually inoperable, once made, so I would like to throw it at you more established players, and see what you think.
As well if you think it works, can the speed control of the servo also be added to this??
Thanks in advance
 

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Minder

Apr 24, 2015
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I don't see how without feedback?
Position OR speed.!
Edit: Probably a RC servo intended, very confusing when just the term 'Servo' used.
 
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Harald Kapp

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Probably a RC servo intended
That is my thought, too. Obviously the 555 creates a pwm signal to control the servo's position. The speed is a property of the servo used. It is up to @bigkim100 to select a servo with the appropriate speed.
 

bertus

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Nov 8, 2019
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Hello,

The circuit is indeed for a RC servo.
It uses pulse width to control the position of the RC servo.
Read this wiki page for more info:

Bertus
 

Bluejets

Oct 5, 2014
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If you want speed control of the servo, forget the whole circuit and go with a basic uC like Arduino, you'll need it.
 

Harald Kapp

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The speed of a standard RC servo is, afaik, controlled by the servo controller within the RC servo block. Not externally.
One can reduce the speed by changing the pwm's duty cycle slowly. This can be done manually (turn the pot of the servo tester slowly) or using a microcontroller (e.g. Arduino).
One cannot increase the speed above the max speed of the servo. At least not electronically. Mechanically: yes, by changing the gear ratio within the servo block, but that's another construction site.
 

Minder

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A single PWM pulse varying between 1ms and 2ms is required every 20ms for full control..
 

Bluejets

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As far as I am aware, the speed of any servo ...(from standard speed to slower) is using the uC to tell the servo to move to a different predetermined small step position (between 1 and 2ms) a number of times.
 

Harald Kapp

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from standard speed to slower
I second that, see post #6.

The position (angle) of a RC servo is controlled is controlled by the width of the pulse (modern servos) or the duty cycle of the pulse signal (older servos), see this link.
Thus you can instruct the servo to change the position by changing the pulse width of the control signal. When you change the pulse width from one pulse to the next, the servo will start to change position to reflect the newly instructed position. How long it takes the servo to arrive at the new position (speed) has nothing to do with the controlling pulse signal. The servo being a mechanical contraption cannot change the position instantaneously. A motor has to be activated, gears set in motion, finally a load has to be moved. This all takes time. How fast the servo can do this depends on the motor's rpm, the torque, the gear ratio, the load etc. Changing the speed of the servo requires either a faster motor or one with higher torque (or both), another gear ratio, or a lighter load.
Apart from the load these are all properties of the servo, not of the controlling signal. Therefore there is no way to increase the speed of the servo by any adjustment to the control signal
As mentioned previously also by @Bluejets , the speed can be lowered by slowly stepping the control signal's pulse width from the starting position to the ending position. In this case the servo will also step through the positions slowly. In my experience this method is not favourable. Rotating the motor by small increments reduces the mean torque available at the output of the servo and increases jitter of the output.
 

bigkim100

Apr 17, 2013
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I would like to thank EVERYONE for their help in this matter. I have designed a circuit to do the job, with everyone's help here.
 
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