Servo current draw

Soundmodul und Fahrtregler in einem Modul
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ColinPT0357
Beiträge: 23
Registriert: Fr 29. Jan 2021, 09:05

Servo current draw

Beitrag von ColinPT0357 »

Guten Tag. I have a relatively heavy model truck controlled by an SFR1. I've noticed the truck will slow slightly when full steering is applied. I suspect this is because I am using a 9Kg servo, which is current hungry but necessary to steer the model. It is running on S Bus and the servo is controlled through the SFR1. Battery voltage is 7.2 My question is: is it possible / safe to run the servo power lead (only) direct to the battery? I'm wondering if a direct voltage feed would lessen the effect it's having on motor control. Any thoughts appreciated. Danke Colin.
Rascal
Beiträge: 3252
Registriert: Do 9. Okt 2014, 01:31

Re: Servo current draw

Beitrag von Rascal »

Hello Colin,
ColinPT0357 hat geschrieben: Sa 28. Jan 2023, 14:40is it possible / safe to run the servo power lead (only) direct to the battery?
that's possible if the servo is a HV (high-voltage) servo, i.e. it must be able to handle up to 8,4V if the battery is fully charged. If the servo is not suitable you may use an external SBEC/UBEC to power the servo with 5V or 6V.
I'm wondering if a direct voltage feed would lessen the effect it's having on motor control. Any thoughts appreciated.
Before you do that I recommend to check if the servo tries to turn too far and hits a mechanical stop when full steering is applied, which would cause it to draw a higher current. Often you can hear the servo buzz in such a case.
If that applies you can adjust the steering rod or apply the servo travel in your transmitter or adjust the steering limit in the SFR-1 (see Configuration > Speed Controller > Steering).
ColinPT0357
Beiträge: 23
Registriert: Fr 29. Jan 2021, 09:05

Re: Servo current draw

Beitrag von ColinPT0357 »

Hi Rascal
Once again, thank you for replying to one of my posts!

The servo can handle 8.4 volts and the steering is limited by transmitter end points so there's no 'overrun', which, as you say, might cause further current draw. No, I notice a slight speed drop and even some dimming of leds with just a moderate steer (not full lock) while running.

Given the above I don't believe I need a separate voltage reg (UBEC) and I would like to try out routing the servo red (+) lead direct to the battery. Obviously the signal and negative wires would stay connected to X5,L. Sorry to ask again, doing this won't damage the SFR1?

Appreciate your help.

Colin T
Rascal
Beiträge: 3252
Registriert: Do 9. Okt 2014, 01:31

Re: Servo current draw

Beitrag von Rascal »

Hello Colin,
ColinPT0357 hat geschrieben: Sa 28. Jan 2023, 21:20 ... I would like to try out routing the servo red (+) lead direct to the battery. Obviously the signal and negative wires would stay connected to X5,L. Sorry to ask again, doing this won't damage the SFR1?
that should be no problem as the higher voltage will only be applied to the servo and not the SFR-1.
ColinPT0357
Beiträge: 23
Registriert: Fr 29. Jan 2021, 09:05

Re: Servo current draw

Beitrag von ColinPT0357 »

Thank you Rascal.
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