Let's Make Robots!

Providing more power

Ok, so i have my Arduino, 3 x servos and an ultrasonic range finder.  Running all these at once from the 5v that the arduino provides is not supplying enough current (i think). I can run at maximum any two of these components from the 5v.

So i guess my solution is that i need to supply the servo's with their own separate power source.

If i hook up some AA batteries to the + wires of the servos connect the gnd to the gnd and the PWM wire to the arduino, will this work? How have other people dealt with this problem?

I'm not really concerned with power efficiency at the moment, i just want to get it working.

Any help is appreciated :-)


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Good plan, keeping the grounds together, go for it. I've run seperate supplies, protected supplies, and single supplies, each can be made to work within reason.

Is it possible to run 3 servos and an ultrasonic range finder from just the Arduino though? I tried and failed. 

So my setup will be Arduino powered by a 9v battery, this will also power the ultrasonic range finder.  The 2 servo's will be powered by 3 AA batteries in series.  Is this right?  This power stuff is confusing, theres no guide that i can find on the net that explains adding extra power.

Those small 9 volts that have the snaps on top to connect power, just cannot deliver enough current to run all those devices. You would be lucky if it powered the Arduino alone.

Now if you are talking about a 9.6 NiCad or NiMh pack, that is another matter. Those have 8 AA batteries typcally and would be able to power everything quite well. 

Servos generally are rated for both 4.8 and 6 volts, and rechargeables are what is intended to be used with them.  I use  4 cell AA NiMh pack with them, and have had this power the micro and sensors I'm using too. THe main problem comes in with usage. If all servos are being driven at the same time, there is a good chance of them "browning out" the micro, resetting it. So either some isolation or even a seperate pack iss needed. 

I'd power your Arduino with a 4.8 volt 4 AA cell pack bypassing the regulator, and run the sonar off that power too. The 3 servos I'd give there own 4.8 volt pack, connecting the grounds between the 2 packs. Or, if you wanted to try, go for a single 6 cell 7.2 volt pack, powering the regulator of the Arduino to run it and a sonar, and have the raw 7.2 volts powering the servos. This is a little beyond spec for the servos and could be a problem depending on the type or brand, but I've heard of people driving  Futabas and HiTecs at higher voltages. 

Does Arduino supply power? I know nothing of the board. My experience of stocl R/C servos is that they can easily draw 500mA at stall, but you would hope not to stall them. So, you're looking at one LS7805 for two servos. My servo controller board has FOUR LS7805s. I've used one for the microcontroller and supporting electronics and three for six servos. My guess would be that the regulator on an arduino might only supply 1A peak.

It simply wouldn't run off a battery of standard AA cells. The likes of a R/C 7.2V NiCd pack will easily supply 12 Amps, though.

I would recommend against the use of a 9.6V battery as regulating 9.6V down to 5V produces lots of heat. Regulating 7.2V down to 5V less so.

Thanks for the reply btw.

Also, are there any formulas i can use to calculate how much power/current everything is going to need? Any one got any links?


Thanks for the help.

Micorcontrollers usually eventually have a current draw spec somewhere. I'd guess the Arduino at under 50 mA. Sonars can vary widely. I think most of the Devantechs are around 30 mA to 50 mA, Polaroid/Senscomp higher (100mA?), Maxbotix lower (3 mA?).

Servos are the power hogs. A Standard can have 50 mA jsut setting there, peaking up to an Amp or more when moving a load. That's why it is helpful for them to have their own supply.

Great, thanks for the detailed responses.  I went to the shops after work and bought a few batteries and a 5v voltage regulator, hopefully that will work...  From what i understand, i can just plug some voltage (9v battery) into one end of the regulator and then connect the out to the servos.

Still i dont know if this will be enough for 3 ill have to test it and see i guess.

You really never know. The more processing your chip is doing the more juice it needs. Although this will be the least of your concerns. the more load you put on your servos, the more juice they'll need. etc. A lot of the time, you basically pray that the circumstance will never arise were all parallel devices are working flat out together. Definitely put servos and motors on a seperate power source, with common ground.