Author Topic: $50 robot  (Read 1383 times)

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Offline rockroboticsTopic starter

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$50 robot
« on: March 11, 2010, 02:20:34 PM »
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,

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Offline chelmi

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Re: $50 robot
« Reply #1 on: March 11, 2010, 02:31:19 PM »
this is equivalent to a regular (DC) motor and a controller.

Offline rockroboticsTopic starter

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Re: $50 robot
« Reply #2 on: March 11, 2010, 02:48:22 PM »
What do you mean controller?
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Offline little-c

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Re: $50 robot
« Reply #3 on: March 11, 2010, 03:51:36 PM »
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.




Offline rockroboticsTopic starter

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Re: $50 robot
« Reply #4 on: March 11, 2010, 03:58:32 PM »
Ok thanks! :)
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Offline YoungGenius

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Re: $50 robot
« Reply #5 on: March 11, 2010, 06:17:46 PM »
So can you use just a regular motor for the 50 dollar robot?

Offline chelmi

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Re: $50 robot
« Reply #6 on: March 11, 2010, 07:39:20 PM »
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.

Offline dellagd

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Re: $50 robot
« Reply #7 on: March 11, 2010, 09:11:59 PM »
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.


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Offline Soeren

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Re: $50 robot
« Reply #8 on: March 11, 2010, 11:18:57 PM »
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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A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
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Offline chelmi

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Re: $50 robot
« Reply #9 on: March 12, 2010, 08:38:11 AM »
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...

Offline rockroboticsTopic starter

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Re: $50 robot
« Reply #10 on: March 12, 2010, 10:11:46 AM »
Ok thanks I get it! :)
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Offline Soeren

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Re: $50 robot
« Reply #11 on: March 12, 2010, 01:53:09 PM »
Hi,

We were talking about modified servo where the feedback mechanism is removed...
I wasn't.


Quote from: Wikipedia
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.

Quote from: pcmag.com
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.

Quote from: yourdictionary.com
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.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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