Power for Serial 8 Servo Controller

I just bought Servo controller today. I’m little bit confused about what voltage and current range for servo controller and servo. I just need two servo and have power supply 9V 0.75A. Can i use this configuration:
Use 9v power supply then step down to 6v for servo controller and 5v for 2 servo. Step down using regulator. Is this enough to power up my servo?

“If the servo battery pack is above 5v, it can also power the servo controller.” Can i supply direct 9v for servo power without supply at the VIN and GND pins. Should i connect across Vcc =Vs?

This graphic has come in handy time and again (this is assuming you have the micro serial servo controller, but connections on the full-size serial servo controller are similar):

So, a little explanation is in order. Your servo power should always be between 4V and 6V. 9V is too much to connect directly to hobby servos (although how long they can take it will depend on the brand).

The serial servo controller has it’s own regulator for the control electronics, so you can hook anywhere from 5V to 16V up to the VIN pins. If your servo power is 5V or less, you can run the servo controller electronics off of the servo power by connecting the Vcc=Vs jumper (as shown in the bottom picture, in this case the power must be applied to the Servo Power pins). This is essentially the same as connecting a wire from your +V power source to both the +Servo Power and directly to the controller electronics, bypassing the on-board voltage regulator. FYI, grounds are all connected internally on the controller.

In your case I would connect the 9V from your power supply directly to the VIN pin, and 4V-6V stepped down through a regulator to the servo power pin. Powering servos through a regulator isn’t the best thing in the world, but a big 500mA-1A regulator should handle two servos just fine if they’re not working too hard. In this setup, you’ll only actually have to connect one ground wire from the power supply to the controller, and it should be to the servo power side ground pin (bigger traces to source more current from the servos). This will leave the other ground pin free for connecting to your serial commanding device.

Does it all make sense now?

-Adam

Hello.

I see nexisnet already responded while I was writing this post. Rather than delete my redundant post, I’ll put this out there as an alternately worded explanation.

You can connect your 9 V power supply directly across the servo controller’s VIN and GND pins. These pins are connected to an onboard voltage regulator that produces an acceptable Vcc for the controller, so you can supply anywhere from 5 - 16 V across VIN and GND.

To power your servos you probably want a voltage source between 4.8 and 6 V. I say “probably” because this is the most common scenario, but there are exceptions to this, so you should check the specs for your specific servos. The current your servos will draw depends on the servos themselves, but it seems to me like 750 mA may not be sufficient for your power needs if your servos will be straining (if you use a step-down regulator with this power supply, I suggest you make sure it can output at least 750 mA). Typically you will want to use something like a 4- or 5-cell NiMH battery pack, which means you won’t need to worry about using a step-down voltage regulator. If you do use a 4- or 5-cell battery pack to power your servos, you can also use it to power your servo controller (i.e. connect the pack across VIN and GND).

You only want to connect the Vcc = Vs jumper if your power supply is under 5 V. The Vcc = Vs jumper bypasses the onboard voltage regulator and uses the servo voltage Vs as the logic voltage Vcc; the regulator is only necessary if your input voltage is above 5 V.

- Ben

Not redundant at all. Somehow I thought that the VCC=VS jumper connected to the regulator, but you’re clearly right (I edited my post above to fix that, now I’ve got a few other threads to track it down in). It’s amazing any of my servo controllers are still working! Lucky for me the absolute maximum power rating on the PIC is 6.5V.

-Adam

Thank nexisnet and Ben for helping me. Really good guide from you two. Thank

Using your hip graphics…is there anything wrong using this option?

Phil

The controller should be fine, since in this wiring setup the power for it is being regulated, so it comes down to weather or not your servos are happy with the battery pack’s fully-charged voltage (which, as you noted in the other thread is quite a bit above the nominal voltage on the label, but also drops quickly).

-Adam