Would someone help me figure out what voltage my ESC is putting out to my Servo?

[Grouper]

Hey everyone!

I Just installed a new servo today ( Hitech HS-5645MG ) and took my scaler scx-10 for a spin with my buddy. The new servo was WAY better than my old 97oz servo, But seemed comparable to my buddys stock axial servo. I was happy with my servo upgrade, but wasnt happy with the comparable power to a stock axial servo, which are half the price as the HS-5645MG.
After I got home I was considering this when I realized, Im running a 7Cell Ni-MH, which will apparently lower my ESC's output voltage to my servo's. (even tho it has a higher input voltage with the 7 cell apposed to the standard 6 cell)

Im running a Super Rooster ESC, the stock axial 2.4ghz micro receiver, and said servo.
The SuperRooster is rated at 6V, 3Amps
Specs: Reversible ESCs

Im just sort of curious here, But Would anybody be able to help me figure out what sort of volts and amps my SR esc is putting out while running my 7cell nimh?

Thanks for any advice or help!

[SMR 510RR]

The BEC output voltage is not dependent on ESC input voltage...

If you want to check what it is just use a multimeter and check between 2 of the power/ground pins on the RX or from the ESC harness.

What are the symptoms that you are experiencing? Lack of power?

With that servo you are in a bit of a gray area between needing an external BEC and making due with the ESCs internal BEC...If you start having brown out issues (your RX and servo cutting out) then you are in need of a BEC capable of putting out more amperage.

[holycaveman]

Exactly what was said.

Also is your steering binding at all?

Are you using a +1" servo arm?

Is your rig heavy?

Large tires?

All this will rob power from your servo.

[Grouper]

Originally Posted by SMR 510RR

The BEC output voltage is not dependent on ESC input voltage....

You Sure about that?

[sloppy]

Originally Posted by Grouper

You Sure about that?

Yeah notice in the specs for your ESC it says 6V/3amp BEC... It does not say anything about input voltage just that the max you will get out will be that amount..

The exception would be if you dont put 6V in... Then your output would be lower.. The BEC does not step up voltage just down..

[Grouper]

Originally Posted by sloppy

Yeah notice in the specs for your ESC it says 6V/3amp BEC... It does not say anything about input voltage just that the max you will get out will be that amount..

The exception would be if you dont put 6V in... Then your output would be lower.. The BEC does not step up voltage just down..

Well Im confused!
This is where I got my info from:

Originally Posted by Chadworkz

Yep...the more voltage you put into the ESC, the less power goes to your servos. You will need a BEC unit to cure that problem (CCBEC or Novak 5A-6V BEC).

In regards to why the BEC drops as voltage goes up. Check out page 4 of this thread. John/Holmes Hobbies provides an excellent explanation of why this is happening.
-Mike

JohnRobHolmes;1131364]The amperage out and voltage in are directly and inversely proportional.

If Tekin assumes 7.2v in to get 3a out at 6v we can do a little math to figure the rest out. A linear BEC bleeds the extra voltage as heat, so with a higher input voltage comes more heat. What Tekin is really telling us is the average wattage that the BEC circuit can dissipate as heat.

Wattage = Amps x Volts

7.2v-6v = 1.2v difference
3a of load
1.2x3 =3.6 watts (of heat)

11.1v input-6v = 5.1v
3.6w/5.1v = 0.706 amps out to make the same heat


So if you run a 3 cell lipo you will have less than an amp available. You could run a CC BEC to get your steering power back because it is a switching regulator and does not have such losses.

I understand the first equation. But the 11.1v equation doesnt make sence.

My 7 cell is 8.4V so...

8.4-6v= 2.4v difference
3a of load
2.4x3 =7.2 watts (of heat)
But how do I figure out the voltage?
Volts is Watts divided by Amps right?
v=wxa
v=7.2x...what amperage do i use? 3 I guess?
v=7.2x3
v=21.6... this isnt right.....

[AreCee]

It is correct as the voltage increases the amperage decreases so when you put in more volts the current drops and the servo's draw can exceed the supply, however, the voltage to the servo remains the same.

[Pete Attryde]

Originally Posted by Grouper

Well Im confused!
This is where I got my info from:







I understand the first equation. But the 11.1v equation doesnt make sence.

My 7 cell is 8.4V so...

8.4-6v= 2.4v difference
3a of load
2.4x3 =7.2 watts (of heat)
But how do I figure out the voltage?
Volts is Watts divided by Amps right?
v=wxa
v=7.2x...what amperage do i use? 3 I guess?
v=7.2x3
v=21.6... this isnt right.....

Basically the voltage coming out of your ESC's BEC will be 6V regardless of what the input voltage is (as long as it is more than 6V).

What will happen is that as the input voltage is increased the output current will reduce as the device is only capable of a certain amount of power.

Pete

[Grouper]

Gotcha!
Its the available amperage which goes down, not the voltage!
Thanks guys!

[tuner]

Yep 6 volts.

[kicker]

Originally Posted by tuner

Yep 6 volts.

Great.

So the stock AE2 should be able to power a Savox 0251 yeah?