Servo motor works like a DC motor

How can to make a servo motor works like a DC motor to run as wheel for a robot, how to program it ???

thanks

By modifying it to be a "continuous rotation servo" (which isn't a servo really). How to do this depends on the servo I believe, but they are also available pre-configured.

First, you have to modify it to be continuous rotation. I like this one:

http://youtu.be/SK8mhnEzcvY#aid=P-Oo1j2n5hw

Program example: http://forum.arduino.cc/index.php?topic=254011.msg1810390#msg1810390

If you do this then you loose all the angle control and the signals that used to control the angle now to a limited extent just control the speed.

The point of a servo is to be able to control the angle, If you want to use it like a DC motor woudlnt it be easier to simply use a DC motor? You can get a small brushed ESC to run the motor from ppm signals and control it in the same way as a servo.

The problem with a servo that is modified to continuose rotation is that the POT inside is very sensitive, and if it moves, then the servo will start moving. A hard knock may be enough to make it start moving,

You can glue the POT in place, but it still isnt a perfect solution.

If it is mechanically suited to the job a continuous rotation servo has a lot going for it - everything is in one neat package that is easy to install and easy to control.

When I modified some servos I took out the pot and replaced it with a pair of fixed resistors. I think this link shows the technique.

...R

If it is mechanically suited to the job a continuous rotation servo has a lot going for it - everything is in one neat package that is easy to install and easy to control.

Agree with Robin2 100% That would be my answer. By the time you can find the motor, gearbox, mounting hardware and wire harness, you can have it up and running with servos. You can buy them Already modified for even less work and replacement is simple.

Dear all , many thanks to you and thanks for reply .

Actually , I am working on design a two wheel-mobile robot that navigates from its initial point to goal point , i want to use two servo motors (which had encoders) one per axis to determine heading angle and coordinate x-y of mobile robot . so is that mean when i modified the servo motor that i wouldn't be able to determine the heading angle and coordinate x-y of mobile robot by enoder of servo ? is there any ideas or advices could help me ? please

many thanks

so is that mean when i modified the servo motor that i wouldn't be able to determine the heading angle and coordinate x-y of mobile robot by encoder of servo ?

No. What that means is you can't tell the servo to go to an angle anymore. Just forward and reverse and at a selected speed.

You still need other circuits for X and Y heading of the robot. Servos don't have anything to do with that.

i want to use two servo motors (which had encoders)

Are these built into the servo?

All servos have a positional sensor of some sort. Normally these are the pots that you break to convert it into a continuous rotation servo.

Some systems consist of just a motor and an incremental encoder, the LEGO mindstorms motors are like this. Here you need to control the motor speed depending on the pulses you get from this encoder. You have to do this in software or by using an ESC.

However a conventional positional servo has no encoder that you can use for tracking its position you will have to fit external encoders to the motor.

Maria88: Dear all , many thanks to you and thanks for reply .

Actually , I am working on design a two wheel-mobile robot that navigates from its initial point to goal point , i want to use two servo motors (which had encoders) one per axis to determine heading angle and coordinate x-y of mobile robot . so is that mean when i modified the servo motor that i wouldn't be able to determine the heading angle and coordinate x-y of mobile robot by enoder of servo ? is there any ideas or advices could help me ? please

many thanks

Or a wildy different approach would be to use this : http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=39478

Its an Arduino Mega with 3axis Gyro, 3 axis Accelerometer, compass, barometer & GPS. It takes some research to figure out how to use all the sensors but you have to admit its a complete navigation package.

Just a thought..

-jim lee