MKS HBL 950 servo doesn't respond


I'm an absolute beginner. I've programmed blinking leds, and some text on a 16x2 LCD. So keep this in mind while we trouble shoot this issue. It coud very well be I did something wrong that is very obvious, so don't assume anything. :)

Currently I'm trying to control a servo.

See website for specs

I've connected the servo to a external power source: a 2S lipo 7.4V 340mAh battery pack

I did this by connecting the red servo wire to the red lipo wire, the brown servo wire to the black lipo wire. I connected the orange servo cable to the the arduino Uno pin 9. I'm powering the arduino by USB

I've used the standard servo.h library with the standard example code I've used the megaservo.h libary as well with the example code to write microsecond

But whatever I try, the servo doesn't respond

I've messured the voltage on the battery, it's 7.4V. SO that should be good :) I've tried a second servo, just to check that the first one isn't a bad one.

I've read some post about PWM en PPM and although I currently don't understand the difference I do understand I although MKS states the servo is PWM driven, I shouldn't try analogwrite. at least, untill I fully understand what I'm doing and what the differences are.

What I'd like to know before I spend another couple of days trying things, is: "Should this servo just simply work with the default servo.h library? Or is this a special servo that needs a different setup?

warm regards, Edward

Do you have the servo ground connected to the Arduino ground?

dxw00d: Do you have the servo ground connected to the Arduino ground?

No, I have connected to the black cable on the external battery only. Should I change that? :roll_eyes:

Should the ground of the sevo be connected to both the arduino ground and the lipo pack or just the arduino?


You should have a common ground for all parts of your circuit, so the lipo ground should be common with the servo ground and the arduino ground - there should be only one ground which is easily achieved by connecting all these grounds together. See the links in my signature for a little more detail.

Duane B

Dxw00d, DuaneB,

Thank you. Instant success.

@DuaneB, thank you for your blog post. Very useful information. I love the fact that you only mentioned the common ground issue..euhm 3 bold.

If only I would have actually accepted the fact that I, as a beginner, could have made a beginner mistake in a 3 wire setup instead of spending hours searching on google on the assumption that it must be a very exotic servo I have, with a very special need for a very special protocol that I don't understand yet... yeah, that must be it... It can't be because I made a connection's only 3 wires..... :astonished: :blush:

Well, at least I had the "external power supply for your servo" thing right. :)

Thank you for helping me out.