I have just bought my first servo and my arduino but i don't have too much idea about electronics and servos. I am reading everything I found but I keep the some dubt.
The thing is that my servo needs a 7V but my arduino uno supplies 5V. I have conected my servo to the arduino and everything works right, but when I conect the servo to a external power source to supply 7V (I keep the other cable to the same pin to control the angle and velocity) the servo locks and doesn't move.
Is there something I am doing bad? I need something more between the power source and the servo?
Would I need a motor shield kit?
Do you have any more specifics on your servo (part number? datasheet?) Many servos are 5V-powered and I'm wondering if you're finding "7V" as being an absolute maximum rather than a normal rating.
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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons
Most servos accept 4.8v to 6v on their power lines - 7v is probably pushing it a little, but it should still work.
Your issue is probably that you didn't connect the grounds between the two power supplies - without doing so, the 5v signal from the Arduino will float in relation to the servo, causing it to reject commands.