Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: javafiend on February 27, 2008, 10:17:45 AM

Title: Figuring power needs
Post by: javafiend on February 27, 2008, 10:17:45 AM

I'm about to upgrade my $50+ robot to 4 servo driven wheels.  I'm currently powering 3 servos, 2 for drive and one for scanning IR, as well as my electronics.  I also plan on modifying my board for separate power for the electronics and servos.  With this in mind, what voltage will I need to effectively run 5 servos and, for future reference, how do I calculate my future power needs?

Also, when I modify my board, will I still need to make sure that both power supplies use the same ground?

Thanks!

Title: Re: Figuring power needs
Post by: Trumpkin on February 27, 2008, 12:37:42 PM

power does not equal voltage power=watts and what you need to worry about is current, which is ma (milliamperes). calculate what battery you need by using Admin's calculator. i'd say you would need atleast a 3000mah battery, just to be on the safe side buy two of these http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=495 and wire them in parallel which is both the positives connected together and both the negatives connected together. that would give you 4600 mah.

Title: Re: Figuring power needs
Post by: javafiend on February 28, 2008, 10:51:57 AM

I'm not sure I understand.  Do I still use a 6v battery pack to power all my servos or do I need a higher voltage?  From what I understand, mAh is how long the battery will run.  So using the setup you suggested, I will be running the servos at 6v just longer than I would with just one battery pack.  Correct?

Title: Re: Figuring power needs
Post by: ed1380 on February 28, 2008, 10:59:53 AM

over 6v most servo's will fry.  more batteries = more mAh = longer battery life

Title: Re: Figuring power needs
Post by: javafiend on February 28, 2008, 11:08:40 AM

Ok, I think I'm clear on it now.  As long as the supplied voltage is withing tolerances I'm ok.  I would just be shortening the life of the battery by running 5 servos as opposed to 1 or 2.  That's why I would need multiple battery packs in parallel.

Title: Re: Figuring power needs
Post by: Admin on March 01, 2008, 10:33:29 PM

Actually its not voltage or mAh that you need to be concerned with.

Its the instantaneous amps the battery can supply, the discharge rate, which is yet another number you'd find on the battery datasheet.

For example, if you have 5 servos running at the same time, and each one requires .3A, that means your battery MUST output 5 x .3A = 1.5A minimum for everything to work.

I've managed to get 7 servos to work with my $50 robot simultaneously using two NiMH battery packs (the discharge rate however isn't listed for them, sorry!).