Servo voltage
 

Would running a HV servo directly from a lipo pack (as in nitro buggies), not provide an ever decreasing voltage, starting from around 8,4V and decreasing.

I know that a lipo keeps a relatively stable voltage, but in my e buggy, my cells starts fully charged at 4,2V and ends at around 3,6V. In a 2s lipo that would be 8,4V to 7,2V or lower, a decrease of at least 1,2V.

I have seen specs on HV servos with a significant difference in the torque and speed specs between 6V and 7,4V.

If you are into consistent performance and handling from the car, would a servo feeded with a slowly decreasing voltage not be annoying. I mean, in a hour long final, that receiver lipo would decerase in voltage and the servo would become slower and less powerfull.

If I use an external BEC, my receiver and servo are feeded with a stable voltage, and the performance (power/speed) stays constant.

I have looked into this and what I gather is the BEC will offer a steady voltage to your servo at 7.4v for example whether it has to step that up or down a little bit.

The downside is that if you are running a lot of gear off the receiver, it will draw more amps and could exceed what you can feed everything at once, so that transponder and those two fans plus a high torque servo might all add up to the be a bit demanding. Sometimes you can steady that out with a glitch buster cap, maybe you have enough coming from the ESC to not be an issue, or maybe you need an external BEC.

From the support folks at Savox I am told that they like to see a BEC used on electric setups. But that direct lipo will work. The reason they like the BEC in play is the steady voltage. The claim from them is that some batteries will dip a bit in voltage as they are hit with a lot of demand from the motor. An ESC has a bank of capacitors in it to smooth that out, but I am sure that the dip will vary greatly based on real life - battery used / motor used / ESC used / vehicle setup / driving conditions.

My advice is to step through it until you have reliable results:

1 - Try your built n BEC.
2 - Then try the built in BEC with a glitch buster.
3 - Then it is time to decide if you need an external BEC or want to wire in direct 2S lipo.

You just quit the list when you have your simplest solution.

In my opinion use 6v servos when electric racing and HV servos when nitro racing with a lipo rx pack. You shouldn't need an external BEC at all and as long as you don't have a Spektrum radio then you won't need a glitch buster either. I wouldn't get all tied up with voltage drop if direct connect to lipo it really doesn't make that much difference. Simple as peas.