BEC and 4ws dual servos, intermittent power

[chalmene]

Long story short, I am getting intermittent/glitchy power when running both servos off a y-harness and a Castle 10-amp BEC.

Here is my gear:

Flysky HV receiver FS-GR3F (4.0 - 8.4V)
Castle 10-amp CC-BEC set to 7.4v
Dual HItec HV HS-7950TH servos (rated at 7.4v) plugged into a Y-harness

I believe it to be my BEC at fault; when I run a straight 2s pack to my receiver, I have no issues. Should I raise the voltage of my BEC, or does it simply not put out enough amperage? Is it safe to run power from my main 2s pack to the receiver?

[EeePee]

Lowering the voltage will allow more amperage. Try 6 volts.

Or wire the servos directly to the battery.

[chalmene]

Originally Posted by EeePee

Lowering the voltage will allow more amperage. Try 6 volts.

Or wire the servos directly to the battery.

They are HV servos, I kinda bought them to run them at 7.4 lol :-P. Would running straight power from the main pack to the receiver give the same results? Any issues there?

[mikemcE]

Put a glitch capacitor on, it might be just enough to keep the servos fed

[EeePee]

I've run a 7950 at 6 volts for years and think ~430 oz of torque is plenty.

Same results as what?

[chalmene]

Originally Posted by EeePee

I've run a 7950 at 6 volts for years and think ~430 oz of torque is plenty.

Same results as what?

YOu said to wire servos directly to battery. Or did you mean the same thing?

[chalmene]

Originally Posted by mikemcE

Put a glitch capacitor on, it might be just enough to keep the servos fed

Just tried this, did not remedy it unfortunately. :P

[EeePee]

Wiring the servo directly to the battery will initially supply 8.6 volts. It will also allow a large amount of amperage to be delivered. Use the ESC's built in BEC to power the receiver.

[chalmene]

Originally Posted by EeePee

Wiring the servo directly to the battery will initially supply 8.6 volts. It will also allow a large amount of amperage to be delivered. Use the ESC's built in BEC to power the receiver.

My ESC BEC only supplies 5v, I want to run my servos on 7.4. I know it can be done, just need to figure out the best way.

[Awesome-Sauce RC]

is the bec powering the rx as well as the servos?



tony

[chalmene]

Yes, Im running the castle bec to the receiver.

I have run hv servos off of a 2s lipo in other applications, just not off the main power pack. Im wondering if anyone does this without issue?

[Awesome-Sauce RC]

if you remove the bec from rx and solely use esc's built in bec to power rx as eepee suggested and dedicate the bec to just the servos with a bypass adapter( didnt see he had already asked that last night when i asked after, tired lol) that should alleviate some/most of the glitching as the rx will not end up browning out with 2 hv servos drawing direct from bec as opposed to drawing from bec via rx ( pcb power traces in rx are not great for high current draw ).

definately keep the glitch capacitor in place regardless as a redundancy measure just in case.

if you have run hv servos from direct 2s before then it shouldnt be any different doing it this time, just more wiring up to do, also your y harness if its just a standard gauge servo wire maybe look into upgrading it for something a little more like a 22AWG or bigger wire just to make sure that it can handle any peak current demands.


tony

[chalmene]

Originally Posted by Awesome-Sauce RC

if you remove the bec from rx and solely use esc's built in bec to power rx as eepee suggested and dedicate the bec to just the servos with a bypass adapter( didnt see he had already asked that last night when i asked after, tired lol) that should alleviate some/most of the glitching as the rx will not end up browning out with 2 hv servos drawing direct from bec as opposed to drawing from bec via rx ( pcb power traces in rx are not great for high current draw ).

definately keep the glitch capacitor in place regardless as a redundancy measure just in case.

if you have run hv servos from direct 2s before then it shouldnt be any different doing it this time, just more wiring up to do, also your y harness if its just a standard gauge servo wire maybe look into upgrading it for something a little more like a 22AWG or bigger wire just to make sure that it can handle any peak current demands.


tony

If I ran everything off my main pack, I would simply splice in a heavy servo lead from my pack to the receiver. My Y is the same guage as my servo leads. The guage will be fine, I and others have run HV on standard guage in 700 class 3d helis and never an issue. That's 4 HV servos drawing 8.4v.

My main concern, and I havent done this before, is using the main pack to power BOTH MOTOR AND RX/SERVOS. Any forseeable issues there as far as power draw? It is a 20C-30C 2s pack. I was hoping to hear from somebody who is doing this, but I guess I may be the guinea pig...

Also in case of any questions, I read this servo is designed to run off 2s power. https://www.servocity.com/hs-7950th-servo

I thought of doing your first suggestion initially, a little more wiring to do but it is an option. And sorry EeePee, I wasn't sure if this was what you meant for sure.

[EeePee]

Far from the guinea pig. No issues. Been done for a dozen years.

[chalmene]

Originally Posted by EeePee

Far from the guinea pig. No issues. Been done for a dozen years.

Right, I was kinda hoping to hear from folks doing it this way though. Just nice to have feedback, being paranoid I guess. Anyway, thanks for the help guys, I think I'll go the single 2s pack / no BEC route then.