# Servo wiring

I am currently working on a robotics project and I am curious as to what the best way to wire servos with Arduino. I will be running the Arduino's power from a 9v adapter and I would like to run the 3 servos from a single 9v. Any advice is welcomed.

Make sure that your supply can provide the current the servos demand. Do you know how much current each one will draw?

It appears that they take 4.8 volts each.

ashtonmehrle:
It appears that they take 4.8 volts each.

That is not what I asked or what you need to know:-

Do you know how much current each one will draw?

Servo data sheets seem to be strangely silent on the current question... you might have to rig up a test with your ammeter in series and measure the current. But you'll need more than just the current under no load: hold the horn to prevent it turning. I tested one recently and it was about 100mA under no load, but rose to about 500 when I held it from turning.

Typical R/C servos are spec'ed to run from voltages in the range of 4.8V to 6V, and 9V is too much. They "might" run at 9V, but will get too hot, and possibly cook. Not a good idea. I run my robots, etc, from packs of 5-6 rechargeable NiMH AA-cells in series, which gives 6V to 7.2V [a little on the high side]. Current draw depends on the exact servos, and can be from 200-300 mA to much more for newer high-torque devices.

JimboZA: Servo data sheets seem to be strangely silent on the current question... you might have to rig up a test with your ammeter in series and measure the current. But you'll need more than just the current under no load: hold the horn to prevent it turning. I tested one recently and it was about 100mA under no load, but rose to about 500 when I held it from turning.

That is because maximum current draw is somewhat beyond the control of the servo as the mechanical load placed on the servo would be the biggest factor on maximum current draw, to up to the stall current of the motor. Some do give 'standby' current (no load, at rest) and some draw only 10 Ma or so in that condition. I always budget 1 amp draw per servo unless it's a particularly large servo moving a particularly large mechanical load.

Lefty

1-Amp sounds a little high for "standard" 44 oz-in servos, probably more like 300-500 mA, under load. OTOH, if you use a 200 oz-in servo, that's gonna be a lot more.

For reference, I once took apart a servo and measured the voltage pulses durectly on the motor. Under low loading, they were about 2-msec long, but as the torque increased, they lengthened to about 8 msec. The current pulses measured on the servo ground lead are similar.

oric_dan: 1-Amp sounds a little high for "standard" 44 oz-in servos, probably more like 300-500 mA, under load. OTOH, if you use a 200 oz-in servo, that's gonna be a lot more.

For reference, I once took apart a servo and measured the voltage pulses durectly on the motor. Under low loading, they were about 2-msec long, but as the torque increased, they lengthened to about 8 msec. The current pulses measured on the servo ground lead are similar.

It's just a budget figure I've used over the years starting with R/C aircraft, and if it's a little conservative all the better for the overall design. So much depends on the specific application, if multiple servos are moving at the same time or not, so it's a pretty hard figure to nail down on initial project scoping. Many applications use battery power so one can just plan on having to adjust the current capacity and 'C' rating as the project evolves. The use of newer BEC modules that utilize switching regulators has been helpful in this regards both for battery duration and current capacity.

Lefty