Servo issues please help!

Hi I am building a robotic arm that uses 2 hitec hs-5685 and 2 more hitec hs-7954sh servos. On the two hitec hs-7954sh servos they have a jittery movement when they are put under load. They have 403 in oz of torque which is more then enough for what I'm lifting. What could stop these servos from doing this. Also I have used other servos on the exact same circuit with no issues. Theses servos are more demanding because they have almost 4 times as much torque as the other servos that I'm using.

Beefier power supply?

Servos can be very current hungry especially under mechanical loads. So how are you powering this array of servos in your project?

Lefty

It's a 3 amp 0-15v variable voltage that plugs into the wall. I felt that would be plenty?

It will do this even with one servo plugged in not a single other servo is in use except for the one.

I suppose a good first step would be to measure the voltage at the servo when the problem occurs.

It's a 3 amp 0-15v variable voltage that plugs into the wall. I felt that would be plenty?

What voltage are you supplying the servos, and what is the actual voltage when the servo is under load? Is this power supply a wall wart that has a switch to select the output voltage?

erik102696:
It's a 3 amp 0-15v variable voltage that plugs into the wall. I felt that would be plenty?

If this is separate power from whatever is powering the arduino board be sure you have a ground wired between this external power supply and a arduino ground pin.

Lefty

PeterH:
I suppose a good first step would be to measure the voltage at the servo when the problem occurs.

I'd be inclined to measure the current too... none of the pages I had a quick look at gave a figure for the current.

And as Retrolefty said, make sure you have the grounds all joined up.