I would think that should be fine too. Just don't leave extra cable hanging off the end. Worst case you can terminate the ends with 50ohm or other smallish resistors and drive it with mosfets or other high current source. The termination should kill any noise, though i don't think it will be necessary. Actually for 50hz you can probably use much larger resistors.

 

The answer is YES. The input resistance of a typical R/C servo is around 18 Kohms. Each one will need about 0.25mA signal drive current so you don't even need the buffer. You did not mention where the signal is coming from so I assume the shield is on a uno. The uno can drive many servos with one output pin. Don't daisy chain the servo power wires. Connect each servo back to the 5V supply separately or you may run into servo "chatter".
Regards,
Keith

 

The answer is YES. The input resistance of a typical R/C servo is around 18 Kohms. Each one will need about 0.25mA signal drive current so you don't even need the buffer. You did not mention where the signal is coming from so I assume the shield is on a uno. The uno can drive many servos with one output pin. Don't daisy chain the servo power wires. Connect each servo back to the 5V supply separately or you may run into servo "chatter".
Regards,
Keith

Are you sure there are not protection diodes? Servo used: Hitec standard, >= 10 years old.

Results:
Diode function: Signal (+) , Gnd (-) Indicator: open circuit
" " : Signal (-) , Gnd (+) Indicator 0.78 (typical for diode)
" " : Signal(+), Vcc (-) Indicator: 0.87 (a bit higher than expected)
Resistance: Signal(+), Gnd(-) Indicator: 30k but continued to rise well past 60k as if charging a capacitor.

Any resistance to Vcc probably won't matter as Vcc => Vsignal.

 

The answer is YES. The input resistance of a typical R/C servo is around 18 Kohms. Each one will need about 0.25mA signal drive current so you don't even need the buffer. You did not mention where the signal is coming from so I assume the shield is on a uno. The uno can drive many servos with one output pin. Don't daisy chain the servo power wires. Connect each servo back to the 5V supply separately or you may run into servo "chatter".
Regards,
Keith

Fantastic information! No one, even the manufacturer could come up with the 0.25mA spec. There is some unsupported information that an RC servo receiver could not drive more than 3 servos. That is what made me think of using buffers.

Just to clarify, the servos are NOT being driven by an Arduino pin. The servo shield that I posted is what provides the control signals for 16 RC servos

 

I got the information about the input resistance from the data sheets of R/C servo control ICs.
The servo shield signal output up to 25mA per pin so you should have no problems.
https://cdn-learn.adafruit.com/downloads/pdf/16-channel-pwm-servo-driver.pdf
Keith.

P.S.Forget what you measured. You are just confusing yourself.

 

I got the information about the input resistance from the data sheets of R/C servo control ICs.
The servo shield signal output up to 25mA per pin so you should have no problems.
https://cdn-learn.adafruit.com/downloads/pdf/16-channel-pwm-servo-driver.pdf
Keith.

P.S.Forget what you measured. You are just confusing yourself.

You are talking about a hobby servo driver, not the servos per se. Do you have any information for the servos that might be relevant to this discussion? BTW, although really cheap servos have a lot in common, not all RC servos are the same.

 

I think you may have confused posts. @KeithWalker said in post #22 that input impedance is typically 18kOhm and each servo should need only about 0.25mA signal current (I'm not sure where the 18k value originated, but good info if it's accurate), and in post #25 that your chosen servo driver shield is good for 25mA per pin so that should be multiples more than what you need for the number of servos that you're running, no buffer necessary.

 

I mentioned above that I got the information on the resistance of the signal input from the IC data sheets.
The older NE544 chip signal input resistance is 18Kohms. The newer ZN409 is minimum 20Kohms.

https://pdf1.alldatasheet.com/datasheet-pdf/view/131848/ETC1/NE544.html
http://www.meditronik.com.pl/doc/plus/zn409.pdf

From the point of interest: I have been into radio control since the mid fifties, long before pulse proportional servos were invented. I built my first four channel pulse proportional transistor superhet receiver and four servos using NE544 chips in 1971. I hand painted the resist on the circuit boards, etched them, hand drilled them and assembled them. The receiver actually still works.The servos are long gone.
I have done a lot of experimenting with servos and arduino boards recently with great success.
Regards,
Keith

 

I mentioned above that I got the information on the resistance of the signal input from the IC data sheets.
The older NE544 chip signal input resistance is 18Kohms. The newer ZN409 is minimum 20Kohms.

https://pdf1.alldatasheet.com/datasheet-pdf/view/131848/ETC1/NE544.html
http://www.meditronik.com.pl/doc/plus/zn409.pdf

From the point of interest: I have been into radio control since the mid fifties, long before pulse proportional servos were invented. I built my first four channel pulse proportional transistor superhet receiver and four servos using NE544 chips in 1971. I hand painted the resist on the circuit boards, etched them, hand drilled them and assembled them. The receiver actually still works.The servos are long gone.
I have done a lot of experimenting with servos and arduino boards recently with great success.
Regards,
Keith

The ZN409 document is dated 1993; copyright 1999. How about something from this century?

As for what you did in 1971, I built my first RC system in 1952. Babcock escapements and so forth. Transmitter was a kit with 135 V Burgess batteries for the plate supply. Neither are relevant to 2020 where a lot of servos are completely CMOS and MCU controlled.

What I reported are actual data. Your data seems to have been lost.

Edit: 1952, if forgot when I was born. Old age is not for sissies.

 

I just made some measurements on Tower Pro micro servos model SG90. They are the cheap ones from Ali Express.
I connected a servo to a 5VDC supply with the input connected directly to the the output.of my pulse generator and connected my scope between the servo input and common.
I set up my pulse generator to give 5V positive pulses, 1.5mS long every 18mS.
I then connected a 50Kohm variable resistor in series with the pulse generator and the servo input with the scope still connected across the servo input.
I adjusted the value of the variable resistor until the scope indicated 2.5V amplitude pulses.
The measured value of the resistor was 12Kohms, so as the resistor was dropping half the input voltage, I concluded that the input of the servo is also 12Kohms. That means that it will draw 0.416mA at the +5V peak. That is almost twice as much current as the 50 year old NE544!
You can't get much more up to date information than that and I guess it also shows that modern high-tech is not necessarily better!

Conclusion: It will work!

Keith

 

P.S. I flew my first home-built radio controlled diesel powered plane from the parade square at RAF Locking in 1956. It was a home made single channel galloping ghost system using a hearing-aid tube, a relay and a small electric motor. I was told later that the transmitter blanked out all the TV sets in the neighborhood.

 

In the 1980's I was given a small boat with a .049 diesel motor in it. I had several .049 nitro glow engines, but this one only had a compression adjuster screw on the head, no glow plug. I was a kid and never found the right fuel to actually get it started, have you seen one of these running? Anyway, I don't want to sidetrack the thread. I've done a bit of RC toy playing myself, and there is typically a night and day difference between the cheapie servos and the good ones, though you pay for the difference. The torque, snappiness and precision differences are very significant. I've had good luck with the Hitec brand, both in cars and helicopters.