50$ robot servo motors

[total beginner]

I'm completely new to this so bare with me but i would like to know which servo motor to get for the 50$ robot because the servo city site said the 8.99 dollar modal has only 90 degrees of rotation and it only rotates clockwise and this confuses me. The part is the Hitec HS-311 servo and i don't want to waste money seeing as i am 13.

[hazzer123]

Hmmm, i think the hitec hs311 has 180 degrees of rotation...

I looked at another site and it says it has 180degrees http://www.eee.deu.edu.tr/~ozkurt/robotics2005/14/hitechs.htm

I have a hitec hs 322hd and that has 180 degrees.

Im not sure why it is wrong, maybe a mistake?

[hazzer123]

Ahhh i looked again, there are two versions. A 180 and a 90 one.

Also i think the clockwise means thats the way it turns with pulses from 1500 uS- 1900uS.

[total beginner]

does that mean that it is able to turn a wheel continuously clock wise or counter clock wise? I'm confused will it work?

[hazzer123]

Ok im not an expert, but servos are normally motors that can move to a certain position depending on the width of the pulses being sent to it. 

It does this using a potentiometer, connected to the output shaft, which changes its resistance depending on how far it has been rotated. Its resistance is measured by the circuit in the servo and thats how it knows where to position the output shaft.

To get continuous rotation, the potentiometer has to be disconnected from the output shaft, so that it no longer rotates when the servo is operating. This means that if you tell it to go to a position other than centre, it will rotate continuously trying to get to that position.

There is a tutorial on this site that shows you how to modify one for continuous rotation, but it doesnt say to modify it in the tutorial. I dont know why?

As i say, i myself am a beginner and may be wrong 

[total beginner]

ok thanks i think i get it

[ed1380]

I don't think it matters, since you'll mod the servo's anyway

[Admin]

Hmmmm appears I didnt specify to modify the servo in the tutorial (its kinda obvious, but not entirely) . . . Ill correct this now!

As for servocity, Ive said this in a few posts . . . dont trust any of the servocity specs for anything on their website. A large percentage of the specs are wrong, and they refuse to fix em . . . Just check the manufacturer websites for the correct info - dont ask in the forum about something you can look up yourself!

When they say 90 degrees, its supposed to be 180.

[sotu]

I have soon built my firsts robot and thinking of my second but i'm not even thinking of using a servo. Not because its better using a motor but i dont really get why buy a servo if u can buy a motor much cheaper!

[Admin]

because you need to buy/make a motor driver to control your motor, and servos come with feedback control (difficult) done for you . . .