Servo control input voltage and capacitance

Thread Starter

mad1

Joined Dec 14, 2010
2
Hi

I'm considering using a servo to control the angle of a small (100g) solar array. This is for a demo project, in which I'll be using a Microsemi SmartFusion FPGA to drive the control signal of a small (Hitec HS-55 or Futaba S-3001/3004) servo.

The FPGA IO's cannot go higher than 3.3V, 12mA

The Hitec site says that 3-5V peak-to-peak is enough for the control signal - this is good.

However, I'm concerned about the input capacitance of the servo control input - is there any data on what this ranges between? What do typical users of these (or other small and cheap) servos drive the control inputs with?

Thanks for any help
 

djsfantasi

Joined Apr 11, 2010
7,873
Servos are controlled by pulses that repeat every 20ms. See http://www.lynxmotion.com/images/html/servo01.htm

An excerpt from the "Controlling Servos" section on this page follows:
"Servos are controlled with a 5vdc positive-going variable pulse width that repeats every 20mS. The pulse length determines the servo output shaft position but the 20mS frame rate is not position critical. The frame rate does need to repeat at least every 20mS or it will lose power or even stutter. The servo was designed for pulse widths that vary from 1.0mS to 2.0mS, where 1.5mS is centered."
 

Thread Starter

mad1

Joined Dec 14, 2010
2
Servos are controlled by pulses that repeat every 20ms. See http://www.lynxmotion.com/images/html/servo01.htm

An excerpt from the "Controlling Servos" section on this page follows:
"Servos are controlled with a 5vdc positive-going variable pulse width that repeats every 20mS. The pulse length determines the servo output shaft position but the 20mS frame rate is not position critical. The frame rate does need to repeat at least every 20mS or it will lose power or even stutter. The servo was designed for pulse widths that vary from 1.0mS to 2.0mS, where 1.5mS is centered."
Thanks for your reply. I understand and know how servos are expected to work. However, my question is specific to the abovementioned Futaba and servos and has to do with minimum voltage and capacitance/impedance and I was looking for that specific information. The 5vdc mentioned in the linked article isn't a minimum control signal voltage, and in fact, contradicts the FAQ on the manufacturer's website (Hitec)
 
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