servo motor controller

Thread Starter

khalillabaki

Joined Sep 28, 2016
7
hello guys,

i need to build an electronic circuit to control a servo motor
the servo i have, doesn't have any electronic circuit in it, just a motor connected to a potentiometer via gears, so 5 wires come out of the servo (2 power wires for the dc motor and 3 wires for the potentiometer).
i want to control the servo with a poentiometer.
the input voltage for the system is 12vdc
the motor is also 12v.
can anyone please help me build this circuit board?

thanks in advance
 

nerdegutta

Joined Dec 15, 2009
2,675
the servo i have, doesn't have any electronic circuit in it, just a motor connected to a potentiometer via gears, so 5 wires come out of the servo (2 power wires for the dc motor and 3 wires for the potentiometer).
i want to control the servo with a poentiometer.
I think you need to add a picture or two of the motor, or at least a link to a datasheet.

Oh... And welcome to AAC. :)
 

Thread Starter

khalillabaki

Joined Sep 28, 2016
7
i dont need continuous rotaion. The purpose of it is to control the throttle valve on an engine, with the potentiometer mounted on the gas pedale
 

crutschow

Joined Mar 14, 2008
23,729
So then you need the circuit to control the motor so that the gas peddle pot position matches the servo pot position(?).

But we do need more info on the servo to suggest a proper solution.
 

MaxHeadRoom

Joined Jul 18, 2013
19,388
You could use a pot on the pedal and another on the valve and move the motor until coincidence occurs between pots.
Have you used any micro processors or just logic IC's.?
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
19,388
There is also another way of making a synchro with two small identical bi-polar stepper motors connected together, one will track the other, no power needed.
Max.
 

Thread Starter

khalillabaki

Joined Sep 28, 2016
7
the motor is 12v 1.4A rated current
The potentiometer is 3k ohm

Im not too into electronic circuit, i just need a circuit diagram so i can apply
 

jpanhalt

Joined Jan 18, 2008
8,298
Now that we know it is for a throttle pedal, is it for a car? If so, what make and model? Is it a repair or are you creating something?

I have attached a drawing for the connections that a Ford electronic throttle uses. By necessity and common sense, there are safety features. I wonder whether this project is appropriate as a DIY for someone with little experience?

John
 

Attachments

Thread Starter

khalillabaki

Joined Sep 28, 2016
7
Yes it is for a home built car, i built it at my workshop. So im creating something not that complicated, just a servo motor to pull the throttle cable according to the position of the potentiometer on the gas pedale.
Im making this system because i have a long distance between the throttle pedale and the throttle valve on the engine, so the cable has high friction and doesnt give accurate throttle response, and sometimes it stucks. In otherwords, im placing the servo near the engine, and connect it to the existing throttle cable but with a shorter distnace now.
 

MaxHeadRoom

Joined Jul 18, 2013
19,388
If you have nothing else but the motor and the pot for the pedal, you are going to need some kind of feedback element such as a pot on the throttle position, and use some kind of comparator/motor correction circuit for each pot position.
Max.
 

Thread Starter

khalillabaki

Joined Sep 28, 2016
7
No, the servo assembly has a motor and a potentiometer connected to it via gears (this is the feedback pot) i need an electronic circuit and a potentiometer on the gas pedale to control the servo. I need to know what pot size i need on the gas pedal as well as the circuit diagram for the controller
 

Sensacell

Joined Jun 19, 2012
2,505
Yeah, the probability of a home brew servo position control going haywire is rather high.

Position servo's like this are far from fail-safe, in fact they love to slam to full scale when any part of the system fails.

Shorted drive transistor? FULL THROTTLE!
Flakey pot? FULL THROTTLE!
Gear falls off? FULL THROTTLE!
In all of these failure modes, you have a 50-50 chance of full throttle- scary.
 
Last edited:

crutschow

Joined Mar 14, 2008
23,729
How much current does the servo take.
Does the motor need to be driven by one polarity to advance the throttle and the opposite polarity to retard the throttle?
 

Thread Starter

khalillabaki

Joined Sep 28, 2016
7
The motor takes app. 0.8A
It does have to be driven in the two polarities. In case of circuit failure, the throttle valve has a return spring to idle position.
 

Sensacell

Joined Jun 19, 2012
2,505
Big spring?

If the motor can overcome the spring to open the throttle, it has then NO UTILITY as a fail safe mechanism.

The motor can easily fail FULL POWER.
 
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