servos and voltage on a esc
 

why is it that as u increase cells (volts) in a brushless esc that the number of servos the bec can drive goes down? its kind of backwards from what i would think anyone got any ideas?

RE: servos and voltage on a esc
 

No, in fact it is simple math ;)

If your servoes draw 2 Amp at the most, your battery is 10 Volt and your BEC delivers 5 Volt to RX/servoes the voltage-drop needed in the BEC is ... 5 Volt. When you starts your calculator you will see that there is a need of getting rid of 10 Watt in the curcuit! (P=U x I) P=5V x 2A giving you 10 Watt... If you put on a battery at 20 Volt the math gives you: P= 15V x 2A which gives 30 Watt! So the main problem is to get rid of heat.

Other factors: the ESC have other jobs to do too, if they should have more sophisticated BECs they would cost more and weigh more.
When it comes to bigger installations the ESCs don`t have BEC at all. Then you use a RX-battery or an UBEC if you prefere. A UBEC with proper capasity have lot of cooling-ribs... the same phenomena happends here of course.

Easy as that...

RE: servos and voltage on a esc
 

I've been looking into this issue ever since my esc shut down after bench testing my mini funtana. It runs 4 servos. All my other planes use 3 so I never ran into this problem in the past. It looks like there are 3 major players manufacturing sbec and bec. They are:

http://rcelectrichobbies.com
http://www.koolflightsystems.com
http://www.aircraft-world.com/shopexd.asp?id=1940

Prices range from $25 to $40. Weight ranges from 10g to 20g.