Reliably powering multiple servos using Uno and wall-wart power

I’m somewhat new to Arduino, and quite new to anything beyond electrical circuits. In order to ramp up on both, I want to tackle a prototype which will (periodically) require an almost constant, simultaneous sending of angle changes to two 5v servos.

I quickly learned that you can’t run multiple servos off USB power. I have recently gotten advice that says not to run a setup with multiple servos drawing power through the barrel plug directly on the Arduino, because a servo under load will greatly challenge the Arduino’s voltage regulation. (Although, I don’t know why.)

In searching for how to put this setup together where the power runs through the breadboard, I’ve put together the schematic in the attached image.

Is this basically correct? Is there a better/smarter way to do it? Why or why not? Any comments you can offer that illustrate the principles of a good electrical circuit would be appreciated, because I haven’t been able to find any verified project walkthroughs or schematics that achieve exactly what I’m attempting here.

I’m also wondering what I might need to alter or consider once I decide what my servos can be used for. I can’t seem to find good beginner’s information on what you may need to put in place if your servos will pull a load of one type or another.

Thanks!

arduino_2_servos_update.png

GregNord:
I quickly learned that you can’t run multiple servos off USB power.

Technically speaking, you can’t even run ONE servo off USB power. Not if you put any strain on it.

GregNord:
I have recently gotten advice that says not to run a setup with multiple servos drawing power through the barrel plug directly on the Arduino, because a servo under load will greatly challenge the Arduino’s voltage regulation. (Although, I don’t know why.)

Finding out why would be an excellant starting point.

Hint: It has to do with “amps”. How many amps can a servo motor draw?

GregNord:
In searching for how to put this setup together where the power runs through the breadboard, I’ve put together the schematic in the attached image.

You can’t really run it through a breadboard, either (and for the same reasons…)

Thanks for responding. But...ugh, I'm so confused. It seems like every concept I research for running multiple servos ultimately proves to have holes in it, either related to current or voltage regulation or something else.

Is there no reliable way to power two or more servos that may experience load in Arduino?

You need a 5-6V power supply (preferably regulated), capable of providing at least 2 amperes, for two servos that are running constantly. Be sure to connect the ground of this power supply to the Arduino ground.

Thank @jremington. Would connecting that power supply to the breadboard & having voltage regulators on the two servos be required in that scenario? Just trying to make sure I'm clear.

Do not use bread board, it can not take the current. Solder it all up on perfboard or strip board.

OK, I think I'm starting to get it. Correct me if I'm wrong, but with a 5v/2a regulated power supply and connections soldered on a (non bread) board, I wouldn't need voltage regulators, and I could power two (or hopefully up to four) servos, even if they experience a load.

Thanks for the input, folks.

Basically yes, although you might not be able to run four servos.

GregNord:
Is there no reliable way to power two or more servos that may experience load in Arduino?

Of course...you just need a separate power supply for the motors. That way the Arduino isn't affected by anything that happens on that power supply.

Something like this would do it: http://www.ebay.com/itm/201123931405

(nb. Item picked at random...)

You could use the same supply for the Arduino as well but if you really want "reliable" then dual power supplies is the way to do it (I've built stuff with four or five power supplies to keep everything separate - make sure the lights aren't affected by the motors, the Arduino isn't affected by the lights, etc).

Good point. Reliable power is exactly what I was trying to figure out. I've seen lots of examples with very, very simple schematics that were probably just mean for learning very basic circuit concepts, but I was assuming they were OK for long-term, consistent or "load-pulling" use. My eyes have been opened to the pitfalls.