Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: rockrobotics on March 11, 2010, 02:20:34 PM
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Hi,
I was thinking about building the $50 robot when I saw the servos cost like $9. But since you modify the servo and disconnect the potentiometer, than wouldn't it be the same thing and cheaper to use just a regular motor? Please answer this question!
Thanks,
Rock Robotics
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this is equivalent to a regular (DC) motor and a controller.
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What do you mean controller?
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H bridge control using mosfets (cause they don't overheat and are cheep), which allows the 3-5volt logic on a micro to control much higer voltages without cooking the micro.
L298 dual bridge driver (google the part no, and get DIP parts, they are through hole, so you can solder them) and a motor will do the same as a servo.
takes more work, servos are easier and have gearing to help control speed. a motor without a gearbox wont have the torque if the robot has much more than neglible mass.
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Ok thanks! :)
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So can you use just a regular motor for the 50 dollar robot?
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So can you use just a regular motor for the 50 dollar robot?
to be more precise, I should have said that it is equivalent to a regular (DC) motor, a gearbox and a controller.
So yes you can use a DC motor for the 50 $ robot, but don't be fooled. It will probably be more expensive and harder to
use than a modified servo.
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Yes
just to clarify, a servo is a motor, a circuit board (decodes the PWM code into motor actions) and a gearbox.
Motors take a positive and negitive voltage
Servos thake a positive and negitive voltage plus a signal, which is a special signal which tells the servo which position to go to. You see, unmodfiied, servos do not continously rotate, the only move to a specific position. Motors will just keep rotating and rotating.
the $50 buck bot has modified servos, which you yourself will modify. a modified servo has been altered so that the circuit board will never think that the motor has reached the correct position, so it will keep rotating and rotating and rotating. so center servo = stop. far left position = max speed in left direction. far right position = max speed in right direction.
To use a motor as a servo, it requires a motor controller, which translates that 'signal' into power of the correct voltage and polarity for the motors, essentially turning them into modified servos.
Make sense?
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Hi,
just to clarify, a servo is a motor, a circuit board (decodes the PWM code into motor actions) and a gearbox.
And the very important positional feedback device (usually just a potentiometer), that tells the internal controller when the servo has reached the commanded position or how far from it it is.
For the (cybernetic) function of the servo, the motor, feedback device and circuit is crucial, while the gearbox can be considered an added convenience which isn't really part of defining what a servo is.
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Hi,
just to clarify, a servo is a motor, a circuit board (decodes the PWM code into motor actions) and a gearbox.
And the very important positional feedback device (usually just a potentiometer), that tells the internal controller when the servo has reached the commanded position or how far from it it is.
For the (cybernetic) function of the servo, the motor, feedback device and circuit is crucial, while the gearbox can be considered an added convenience which isn't really part of defining what a servo is.
We were talking about modified servo where the feedback mechanism is removed...
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Ok thanks I get it! :)
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Hi,
We were talking about modified servo where the feedback mechanism is removed...
I wasn't.
Servomechanism
A servomechanism, or servo is an automatic device that uses error-sensing feedback to correct the performance of a mechanism. The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position or other parameters. For example, an automotive power window control is not a servomechanism, as there is no automatic feedback that controls position—the operator does this by observation. By contrast the car's cruise control uses closed loop feedback, which classifies it as a servomechanism.
An electromechanical device that uses feedback to provide precise starts and stops for such functions as the motors on a tape drive or the moving of an access arm on a disk.
servomechanism definition
an automatic control system in which the output is constantly or intermittently compared with the input through feedback so that the error or difference between the two quantities can be used to bring about the desired amount of control
When you remove feedback, it stops being a servo and the name is just used because it originally was.