Seeking external power for multiple hobby servos

Hello all, long time since my last post on here.

I've been doing some research over the past few days to try and work out exactly what I need, although I'm having trouble forming a definitive strategy. Here goes:

I'm working on an installation at the moment that uses 6 continuous rotation hobby servos (http://www.oomlout.co.uk/servo-continuous-rotation-p-235.html) and 3 micro servos (http://www.oomlout.co.uk/servo-micro-p-195.html) Rather naively, I had been using my Duemillanove's 5v pin and was getting away with it, although I know now that this isn't a viable method:

http://www.youtube.com/watch?v=f_7Jmp7hjZs

I was thinking about picking up something like this: http://www.coolcomponents.co.uk/catalog/breadboard-power-supply-5v33v-p-806.html Would it be sufficient? I'm trying avoiding changing my setup too much and just focusing on getting enough power for all of the servos (avoiding additional shields etc.)

I'd be very appreciative of any advice/input people might be able to give. I just wish I'd read about how much power these things need sooner!

P.S. I'm fairly certain this is a power related issue. If it's not, here are the symptoms: the servos move erratically when I attach more than a couple, although it's not always instant, as you can see in the video. I've gotten away with it for prolonged periods before but sometimes they start juddering as soon as the Arduino gets power. I've even had a couple of kernel panics recently :~

Servos can grab large currents when they move, allow say an amp per servo if moving at same time. Usual method for powering them in an RC setup is from 4-cell NiMH or NiCd rechargeable battery pack (around 5V), or a BEC rated at 2A.

A 5V or 6V regulated wall-wart supply of several amps might be simpler. You can also try to measure the actual current load of one of your particular servos in action to get a feel for what they really need.

It is not a good idea to put servos directly on the Arduino 5V rail, its asking for problems.

Thanks for the quick response, MarkT.

Any ideas what sort of wall wart would be okay to use with that breadboard power supply I linked to in my first post, based on my requirements? Unfortunately, I don't really have any means of measuring what's going on with the servos and my electronics knowledge is fairly basic.

And yes, I know now that the Arduino's own 5v isn't what I should have been using. I live and learn!

I mean instead of that breadboard supply (its a poorly designed board, the PCB traces are too thin for the 1.5A regulator it has, they will likely overheat if you use it in anger, and it can't do 6A if that's what your servos need).

Power the servos only from the wallwart (6V is preferred to 5V), common the grounds with the Arduino. Give Arduino a clean 5V (that breadboard supply would work at low currents for instance, but the Arduino has its own regulator on-board.

Okay, I'll not bother with the breadboard supply. To power the servos from the wall wart, do I connect it to the Duemillanove's power input and use the VIN pins instead of the 5v pin?

Sorry if this sounds frustratingly noobish but I've never used any external power for the Arduino. I very much appreciate the advice you've given so far!

jrmedd: Okay, I'll not bother with the breadboard supply. To power the servos from the wall wart, do I connect it to the Duemillanove's power input and use the VIN pins instead of the 5v pin?

Neither. The Vin pin has a 1 amp total current limit due to the polarity protection diode wired between the external power connector input and the Vin pin. You need to slice into external power before it enters the arduino. If the external power source is not also wired to the arduino external power connector then you also have to make sure the external power source ground for the servos is also wired to a arduino ground pin. Keep in mind that servos require 4.5 to 6.0vdc power and the arduino external power connector requires like 7 to 12vdc, so it can be a little tricky properly powering both an arduino and multiple servos from the same supply. I know this is probably more confusing then helpful. A single external 5vdc regulated power supply rated at enough current for all the servos and the arduino can be made to work by powering the arduino by wiring to the +5v and ground pins on the arduino.

Sorry if this sounds frustratingly noobish but I've never used any external power for the Arduino. I very much appreciate the advice you've given so far!

Thanks for the advice, retrolefty. I looked into the Vin thing myself yesterday and realised that it wasn't the right approach. I'm hopefully going to get together with a local Arduino group soon and see if they can help me find exactly the power supply I need. I know I need a 6v supply with enough amps to get all of the servos going, I just don't know exactly where I'm going to get it!

Additionally, given that I had managed to run all of these servos using my 5v pin and USB power for the board (see the video in my first post) but cannot do so anymore, would you say I've done any lasting damage to my Duemillanove?

Thanks for all the help so far, this is a really good learning experience for me!

Also, when I do eventually track down this 6v power supply with a minimum of 6A, I take it I can still power the Arduino via USB and just use the external power for the servos...provided I connect the ground of the supply to the Arduino's ground too?

Could any UK users recommend where I get my external power supply from?

jrmedd: Also, when I do eventually track down this 6v power supply with a minimum of 6A, I take it I can still power the Arduino via USB and just use the external power for the servos...provided I connect the ground of the supply to the Arduino's ground too?

Correct. Also your new external power supply can be rated for 5vdc rather then 6vdc. 5 volt regulated supplies are much more common and cheaper then trying to find a regulated 6vdc supply. I've always found the best deals on power supplies via E-bay rather then retail suppliers, big difference in prices as the E-bay offerings are often new old stock or new or used surplus.

Could any UK users recommend where I get my external power supply from?

Excellent, thanks. I think I might just get somewhere now.

I’ve seen some wall warts on eBay offering 5vdc - 8A.

Should I trim them like this guy: http://www.instructables.com/id/Groovin-Grover-A-Microcontroller-based-Marionett/step3/Construct-Servo-Power-Supply/

…or is there a more convenient solution for what I’m trying i.e. on the breadboard?