Servos vs DC Motors?

Is a servo the same thing as a DC motor? I am wanting to experiment with either with the arduino. I am looking for some that could be driven by the arduino's power supply. Would this one work? http://www.radioshack.com/product/index.jsp?productId=2102828&filterName=Category

I don't know what I want to do with it yet but want to learn how to control them with the servo library.

As usual, RatShit leaves a lot to be desired. There is no indication about the current requirements for the motor. One of the comments says that the motor will draw up to 1.5A. If that's true, it'll fry the Arduino if you try to power if from a digital or analog pin.

Servos and DC motors are not the same thing. A DC motor spins and spins. A servo has an encoder built in, so that the motor can turn to a specific position, and stop, at a repeatable place, and hold there until commanded to move again. Typically, they are used to control steering and throttle on RC cars, and flap and rudder positioning on RC airplanes.

No, they're not the same thing. A (R/C) servo has a built-in controller and is driven by a simple single line pulse position modulation signal at around 50Hz. They are not capable of continuous rotation, but can be positioned to a reasonable degree of accuracy to a given angular displacement. A servo usually contains a DC motor.

A DC motor needs to be driven by a pulse-width modulation signal at a much higher frequency, and needs at least two signal lines, one for speed and one for direction. It is usually capable of full rotation, but not accurate angular displacement.

Thank you for the explanation. Is there a forum favorite site to get servos from?

eBay ;D.

Well, from some of the replies, I'm baffled because if you go to Adafruit you can get a continuos rotation servo. It has a speed of up to 60 rpm. http://www.adafruit.com/index.phpmain_page=product_info&cPath=34&products_id=154&zenid=c024fcf1859f93413f102e4fdb311816

I hooked one up with the servo program which involves a potentiometer. I think I changed the map to 0 to 360 instead of the 1 to 179. Not sure but I know I got it to work. Anyway when you turn the pot one way it goes forward (cont) and the other way reverse (cont). Works just like a slow rpm motor.

Well, from some of the replies, I'm baffled because if you go to Adafruit you can get a continuos rotation servo.

These are standard servos which have been modified in some manner to allow continuous rotation; using the term "servo" with these is kind of a misnomer, as they are no longer servomechanisms, but rather gear motors with a built in controller for direction of rotation dependent on a specific PWM signal for command input.

It used to be that you had to modify a servo to get it to continuously rotate, but now some manufacturers sell them pre-modified (they can be useful in certain R/C contexts), or vendors modify them and then re-sell them as modified.

I have never ordered from them, but they seem to offer very cheap servos (not as cheap as direct-from-china ebay sellers, but almost as good), plus a lot of other hobby R/C parts:

http://www.hobbycity.com/hobbyking/store/uh_index.asp

These guys are expensive, but they offer some interesting higher-power servo solutions:

http://servocity.com/index.html

:)

this information on the adafruit page is wrong

To control with an Arduino, we suggest connecting the white control wire to pin 9 or 10 and using the Servo library included with the Arduino IDE (see here for an example sketch). Position "0" (1.5ms pulse) is stop, "90" (2ms pulse) is full speed forward, "-90" (1ms pulse) is full speed backwards

0 is full speed in one direction, 179 is full speed in the other, 90 (plus or minus a few degrees depending on the servo) is stopped.

I think I changed the map to 0 to 360 instead of the 1 to 179.

thats not correct, change it back the way it was.

Then try slowly moving the pot and see if you can control the direction and speed You do

Is there a forum favorite site to get servos from?

I do not speak for the forum, but I have been pleased with these $2.77 Mini servos from hobbypartz.

http://www.hobbypartz.com/topromisesg9.html

They're probably not as accurate nor as powerful as the more expensive or larger models, but they good enough for my use.

I’ve been a fan of servos since my early days in RC Cars. Back then I used to use Tower Hobbies (www.towerhobbies.com). LOTS of choices.