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Servos are (usually) DC motors that allow you to control the angle of the axle. The way they do this is by packaging a motor, potentiometer, gears, and a small circuit board in a plastic case. The pot and motor are attached together by gears and the electronics attempt to use feedback from the pot to maintain a position with the motor.
Servos are controlled by pulse width modulation on the control line. Details of how PWM works are easy to find online, but the frequency and duty cycle/actual pulse duration for hobby servos is rarely right there beside the ad for the servo… (I think this is actually because most people that use servos use them in pretty standard hobby situations like RC airplanes. And for those applications all of the PWM is taken care of by other hardware) Fortunately because of these standard application the PWM details for most servos are the same if you’re like to do it the fun way…
Pulse width: .9-1ms = all the way one direction, 1.5ms = center range, 2-2.1ms = all the way the other direction.
Unlike other small DC motors PWM on the control wire allows the actual motor in the servo to use all of the power of the other two wires, while the electronics and control line allow control. (Ground for the motor and control line should be tied together in your circuit, but the supply power could/should be a higher currect source (staight to the battery usually) than your average chip producing the PWM)
Normal Servo (ROB-09065 and ROB-09064) usually have a movement range of 90 degrees. You can get ones that do 180/360+ degrees.
I’m sure PWM on the arduino is a breeze, in fact I know there are already libraries for servo control that let you just drop in an angle… If your slightly more hardcore you can drop your favorite uControler in a breadboard and look through the manual (I mean ask someone on a forum/irc channel) for PWM details…
…yay comment length limit…next time i’ll use feedback, but as it was just in you news i couldn’t resist
1000uS is full speed forward
1500uS is STOP
2000uS is full speed reverse
…anything in between gives a proportional speed. Very handy.
We’re looking to battery power this ‘bot. Does anyone know what current they draw? (on the power supply lines not the signal line)
Cheers
include
}
Sorry about the technical language… If I’m not mistaken, a glossary of terms used here can be found on Wikipedia.
Here is the code I am using (right now, I am only at 1 servo � trying to get the sensor right first) :
include
int potPin = 0; //analog pin used to connect the sensor
int ledPin = 9; //select pin for the servo
int val = 0; //variable to read the value from the analog pin
void setup()
{
myservo.attach(9); //set up the servo as usual
pinMode(ledPin, OUTPUT); //variable to store the value coming from the sensor
Serial.begin(9600); //for watching the speeds in the serial monitor
}
val = analogRead(potPin); // read the value from the sensor
val = map(val,0,600,0,255);
if (val>80) digitalWrite(ledPin, HIGH); //turn the ledPin on
else if (val
I figured it out after I opened the servo, which wasn’t needed.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1278145608
I successfully plugged in 4 at once to my Duemilanove on 4 different pins and ramped all of them up and down, backwards and forwards with the sample code at the url. No other driver/shield/h-bridge needed.
Grab some when they go on sale again!
Can you control the speed of these motors? My thought was (if it’s possible) pulse widths further from the 0 position would result in a somewhat faster speed.
[zero position = no speed, max+ position = fastest in 1 direction, min- position = fastest in other direction]
Is this the case?
-Yes it does operate with speed control (using different PWMs)
if you need just a standard servo with position control then i suggest:http://www.sparkfun.com/commerce/product_info.php?products_id=9064
Yes you could but it would damage the servo if you operate the it above 6 volts
Drawing…
http://www.springrc.cn/en_index/view_list.asp?id=235&typeid=61
Gears…
http://www.servocity.com/html/servo_mount_gears.html
this looks like a pretty standard servo, but a non standard supplier…i dunno what to else to tell ya.