Futaba S3003 servo current draw?

Dunno but 9gm HS55's peak at about 250mA, a bigger one might be up to an amp or so.

Plug a meter in and try...

Figure on 125ma, but it can easily go as high as 3-4 amps with large control surfaces at high speeds...

Cheers,

Bill

To date the testing we have done tends to indicate STANDARD servos (42 to 50 ounce inch range) stall at about 250 to 270 ma. It is reasonable to assume that higher torque servos draw more power.

That's complete bollocks - you'll never draw an amp out of a 3003, more like

1/4 to 1/2 an amp absolute tops. You only get just over an amp from something like a 9450, let alone a piddly little analogue device like the 3003.

Thanks for the help. Got it (motor only) working on 12 volts. Only using the motor with limit switches for an open /closed servo.

Cant get a reading with our meter as it is digital and to slow ro read before the servo hits the stop.

Gary

I'm surprised you haven't let the smoke out of that servo... It's designed to operate on 6VDC max... It may work a while as long as you're not using the internal circuitry.. But I'll bet stall current will cause a meltdown in short order...

Bill

Grab hold and don't let it turn for a quick reading. Stall current will be a good indication of maximum current draw. Startup may be higher, but it is so short, as to not impact the real world very much.

On 2006-11-11, Six_O'Clock_High

Ooops! Make that 2pi inches, so double everything:

Corrected version: 15W, so 2.6amps.

Revised: power losses of 40%, 6W heat output. Not too extreme.

Revised:

stall at 250ma -> at most 1/8 of rated torque (!) draw 4A -> modest inefficiency, and some heat.

OK. With the new numbers, I'm thinking I'd design for 3A to be safe...

--John (with egg on his face)

but is the speed quoted at zero load or full load I suspect its either

57oz of torque or .16/60deg not both

OK...OK.....OK

I measured two 3003's (used) with virtually identicle results.

Idle current = 26ma Unloaded transit current = 105ma Stall current = 430ma

This was with a 4.8 volt nicad pack at 5.1 volts. I have no 6.0 volt packs with which to test.

I think I read somewhere in this thread that the original question poser was thinking of using these servos with 12V. That should be interesting, at least for a few minutes.........

I just tried a 3001 with a 6v pack (note the resistor I was using wasn't real accurate, so I'd allow 10% error, and the 6v pack might have been a little flat). I used a digital scope to calculate an average draw - it's more accurate than a normal meter as it can interpret the current-draw waveform in a more meaningful manner. Idle: 14mA Very lightly loaded transit: 60mA Stall: 500mA

Interesting :) but wouldn't that only be correct if the motor was directly connected to the servo arm?

Nope: a certain amount of power goes into the servo mechanism; as a result, it does a certain amount of work over time, and generates some heat. The "power in" has to equal the "power out" (which is why "power" is a thing that's worthwhile to define as a physical term!). If you have a 6-to-1 gear-down, then instead of 57in-oz of torque, the motor only has to produce 9.5 in-oz of torque...but it does so over a far greater distance (i.e., it has to make 6 times as many revolutions). The net power consumption is the same as if you had a tougher motor, turning slower. (Ignoring all frictional losses, etc.)

--John

The point that was made earlier by someone else, which completely belies your analysis and which seems to have totally escaped your attention, is that the specifications of servo maximum torque and speed are made in such a way as to prohibit multiplying the two to get the servo output power. This means that the power figure you used to start with is completely specious and so working back to get a current draw is also meaningless.

I have measured high(ish) torque Futaba 9450 servos stalled current draw at 6V to be around 1.1A, 3A might just possibly apply to some very high end servos but not to any "standard" analogue servo currently available.

The answer about "power in = power out" was to a question about gearing, and independent of the torque-and-speed-simultaneously issue.

As for the torque and speed ratings being independent, it's pretty safe to say that their product puts an UPPER BOUND on the power draw; since I was only trying to see whether the "5 or 6 amps" (or whatever was claimed) figure was reasonable, using this is a good first shot. If the product had come out more than 6 amps, I'd have learned nothing. Since it comes out considerably less, I can dismiss the 6A figure (or figure that the heat losses would have to be huge).

Actually measuring is clearly a superior method for finding the true numbers; I just happened to be at work and trying to use the information at hand to do a back-of-the-envelope sanity check on a figure that sounded odd to me.

--John

Oh, well I should have read that more carefully then.

Fair enough :-)

I had to think hard to see where your reasening went wrong. But its at this point. You assume that at max torque the servo still manage to do

60 degrees in .16 seconds. But it does not. At stall torque it either stalls (no power in the movement) or it moves very slowly (again very little power in the movement). The current then only depends on the current the motor draws to generate the torque. And that is in a DC motor totally dependent on the resistance of the coils of the motor.

Peter.

SNIP

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Is this akin to pigs flying?