Problem with Arduino & Domanrc 270 degree servo

I'm using Arduino Uno R3 & Futaba S3003 servos hooked up to the PWM pins on the Arduino Uno.

This works fine (The Arduino Sweep program runs fine etc.).

Now I need a rotation angle >180 degrees so i ordered two domanrc DM-S0903MD (270 degree servos).

When I replace the Futaba servo with the domanrc srevos, nothing happens.

Running the sweep program makes the servo "tick" silently, but no movement.

I was at least hoping to see them rotate 180 degrees (as the Futaba servos do),but nothing.

If I start the sweep program and manually turn the domanrc servo approximately 90 degrees it starts sweeping.

This works until I stop the program (by uploading it again or disconnecting the servo cable & reconnecting it.

Both domanrc servos behave identical, so my guess is that the servos are ok, and this problem has something to do with the pulsewidth/ pulse frequency definitions in servo.h/servo.cpp.

(I know there is a 180 degree position limit in servo.h/servo.cpp but nothing works between 0 degrees and 180 degrees either).

I have also tried defining puse interval in microseconds in the Sweep-program

i.e

servo.attach(5,500,2500)
servo.writeMicroseconds(1500);

etc.

but the problem remains.

( I hope that somebody can help me figure out how to solve this (tests to perform etc.)

My Arduino software version is 1.8.3

/Gurra

How are you powering the servos? Those domanrc servos will need a lot more power than a basic S3003. Servos just sitting there twitching usually means they don't have enough power to overcome the initial inertia and the fact that they will run when you have done the initial movement for them makes this even more likely.

Don't try powering them from the Arduino. They need separate power direct to the servo. 4 x AA batteries should be o.k.

Steve

Yes !!!

Problem solved !!

I changed the servo supply to an external 5V supply, with no success, and then a 6V supply, (equivalent to 4xAA, according to your instructions), and now it works like a charm !!!!

The Domanrc spec says 4.8-7.2V, but 6V did the magic...

Thank you Steve for saving me MANY MANY hours of troubleshooting !!

/Kind regards: Gurra

What are the specs on your 5v supply that did not work? I wonder if it failed to maintain 5v under load.
Is your servo loaded or simply spinning freely?

That servo is very high torque, so its probably needing 3A or so peak current.
Even standard servos want 1A or so, its a common mistake to underpower them because the
RC kit manufacturers never produce proper datasheets with stall currents on them.

You can estimate the input power of a servo from the mechanical output (torque x speed). Allow
a factor of two for losses and gear friction.

multiply torque in Nm by speed in rad/s, that's the mechanical power figure. Double that and
divide by supply voltage for an estimate of current.

So a 12kgf-cm servo with 0.15s per 60 degree is 1.2Nm in sensible units and about 7 rad/s.

1.2 * 7 * 2 = 18W. 18W/6V = 3A.