Low voltage to servo

Hi, I was wondering if anyone knows what happens to a regular 4.5-6V digital servo if the voltage is lowered to about 3.7V, apart from lost speed and torque? Will the servo stop working all together?

Kalveo:
Hi, I was wondering if anyone knows what happens to a regular 4.5-6V digital servo if the voltage is lowered to about 3.7V, apart from lost speed and torque? Will the servo stop working all together?

Depends on the specific servo, but at best it would be very erratic in operation if it operates at all.

One thing that can happen is it burns out. With inadequate supply the circuit
may malfunction and pass full supply through the servo's motor, until it overheats
and gets damaged.

If the device has a datasheet or specifications, read those. If unsure either
avoid the unknown behaviour, or be prepared for failure. Small servos aren't
going to break the bank to replace of course...

Also note that if one servo works out-of-spec, another identical one might not -
there is "manufacturing spread" in performance and the specifications are
the worst case performance.

One thing that can happen is it burns out. With inadequate supply the circuit
may malfunction and pass full supply through the servo's motor, until it overheats
and gets damaged.

I doubt that the motor will be damage due to low voltage. I've never heard of RC hobby servos being damaged by trying to power them from somewhat discharged batteries.

zoomkat:

One thing that can happen is it burns out. With inadequate supply the circuit
may malfunction and pass full supply through the servo's motor, until it overheats
and gets damaged.

I doubt that the motor will be damage due to low voltage. I've never heard of RC hobby servos being damaged by trying to power them from somewhat discharged batteries.

True but I think MarkT was thinking under a premise of some near-impossible circumstances, that -could- damage a servo, under a -very- specific circuit.

At first this didn't make sense at all: 'With inadequate supply the circuit...' 'pass full supply through the servo,' because inadequate supply -implies- 'less than full supply,' and is therefore non-possible.

The one case where it's possible is if a circuit is controlling the servo voltage level, and that circuit is powered from a different source than the circuit power source, and goes wonky when the -circuit- voltage level drops, while the -servo- power source is still -capable- of delivering a higher voltage. But that's got to be a rare-rare design. (Mmmm maybe not extremely rare, but Occam's razor says to think as 'simply' as possible unless advised otherwise.)

What I believe OP -meant- in -typical- design is that servos and control circuit are powered by the same source. Or I have to at least -assume- that because he didn't state anything different (again Occam's razor.) With that it depends on how the controller behaves when voltage is lowered. Yes, servos may go to wonkland, because controller has also gone there -first-. But other than that, no, simply low voltage can't 'hurt' a servo.

Bottom line though is that any assembly (especially with a non-simple power source design) that has -potential- to hurt either itself or people around it should have some sort of voltage sense circuit, plus a signal to the controller circuit, plus constant monitoring of that signal, so it can shut everything down safely if voltage drops below a certain level.

The point is if the servo malfunctions due to low supply voltage (ie its microcontroller
crashes) then it might do anything, including switching the motor's H-bridge
full on. The motor turns to the end point, pulls stall current and overheats...

It might equally well do a sensible thing and just switch off and wait for better power.

Different makes will have different behaviour, and it usually wouldn't matter
as undervoltage is usually a flat battery (unable to sustain high currents for long).

Mains powered motors can suffer from this kind of issue during a brown-out,
since the reduced voltage can lead to stalling at startup (such as in a fridge),
leading to overheating and damage (modern motors should have a thermal
cutout since there is otherwise a real danger of fire).

Thanks for all the replies.
I was just able to test this with a variable supply, though I did only test one servo.
I used a 1 second sweep from 45 to 135 and back continuosly while slowly lowering the voltage. As expected the servo slowed down more and more but still seemed to work all the way down to ~3.0V at which point it started to flutter back and forth (+-10 degres or so) quickly. Increasing voltage back to >3.0V restored it back to the sweeping movement.

So my conclusion is that, even with some spread, there should be no problem running the servo of one LiPo cell (3.7V).