HV Servo Jumps Around

[yoraish]

Hi,
I am running a Hitec HS7954SH on my truck and every time I start off a new battery ( 8.4V) the servo starts to twitch and move very fast for small angles. When the truck is still, the steering works fine, although it starts "jumping" at low speed. It mostly stops at high speeds. Because the servo is rated to run on 2s LiPo, it gets power straight from the battery pack (signal and ground are connected to the Rx).
I'm not sure if the problem is the changing voltages or some sort of interference with the signal. Any help will be great!

Thanks!
Yoraish

[83GT]

I believe you need to pull the servo gnd out of the RX and run it directly from the battery as well.

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[Charlie-III]

Digital servos tend to "hunt" for "0" with a little load on them. If you lift the steering end of the rig up, the "hunt" tends to stop.

With a fully charged pack, the hunting may be more noticeable.

Some radios (Spektrum is one) want a common ground between the servo, RX & power source.

[Olle P]

I'm with Charlie on this.
My servo behaves the same, a little twitchy as it tries to find its zero state. Quite normal.
And I have the ground common through separate BEC and ESC (via Rx).

[yoraish]

Thanks for your answers.

Originally Posted by Charlie-III

Digital servos tend to "hunt" for "0" with a little load on them. If you lift the steering end of the rig up, the "hunt" tends to stop.

With a fully charged pack, the hunting may be more noticeable.

Some radios (Spektrum is one) want a common ground between the servo, RX & power source.

Lifting the truck physically is not solving the problem.
I uploaded a video so you can get a better look at the situation.



You can see that the steering works fine in the beginning, but freaks out at low speed.

[mark32]

u need to add a bec it is causing ur rx is browning out

[Charlie-III]

Originally Posted by mark32

u need to add a bec it is causing ur rx is browning out

He is running the servo direct off the battery pack...... not the RX...... why does he need an external BEC?

[envious8420]

Ive found the 7954sh servos dont respond well being hooked directly to the battery. a bec at 7.4 works well. a fully charged 2s is 8.4v which is too much for the 7954sh. I use one in my losi ten scte with out ever a hicup, but fried another hooked direct to the battery in the wraith. A bec is the hot ticket to run on this one for hv.

[yoraish]

Originally Posted by envious8420

Ive found the 7954sh servos dont respond well being hooked directly to the battery. a bec at 7.4 works well. a fully charged 2s is 8.4v which is too much for the 7954sh. I use one in my losi ten scte with out ever a hicup, but fried another hooked direct to the battery in the wraith. A bec is the hot ticket to run on this one for hv.

Thanks! I'll definitely try out a bec. Is there a big difference between a bec that outputs 6Amps or 10Amps?

[envious8420]

powering the servo, no noticeable difference.