I don't want to put it down too much simple but let's try:
where "P" is power,"V" is voltage and "i" is the current. (Units of measure [Watt], [Volt], [Ampere] )
if we keep "i" costant, we have:
11,1 * i > 7,6 * i
e.g. 11,1 V * 1A = 11,1 W > 7,6V * 1A = 7,6 W
The result is that a 11,1V battery can spin the lens motor phisically faster than a 7,6V battery,
if there are no differences in circuits, I mean, amplificantions, cuts, stabilizations etc etc etc, and obviously the lens must be designed to accept a certain range of potentials.
Things are not so simple, but this is only for exemplification purposes.
The stepping motors have a set resistance on the windings. It does not matter which camera or battery you are using.... the resistance stays the same.
The pertanant equation is P=E^2/R, or Power = Voltage times voltage divided by resistance. I don't know what the resistance is, so we can not compute what the power is, but we can calculate the ratio of power using an 11.1 battery against a 7.6 volt battery. We get (11.1*11.1)/(7.6*7.6) or 2.13.
A camera using an 11.1 volt battery has twice the power to drive a lens stepper motor than a camera with a 7.6 volt battery....... but remember that this is only one factor in AF speed.... there is how accurate the af sensor is, how fast the camera's computer can interpet the results, the search algorithm, and probably a dozen other things that I am unaware of. The battery voltage is just one part of a very complex system.
Since the motors are USM, it means they are driven by an AC current rather than DC. (In this case >20kHz.)
Strictly speaking; AC motors/ transducers have an impedance, not a resistance.... An Impedance changes with Load (in this case torque needed to move an element) so the same motor may present a different impedance, there would be other factors like the angle of the load... all this complicates things a bit.
Seems that the Canon USM motors have a good spread of voltage tolerances, this would enable them to use similar motors (volume/ scale efficiencies) in many different lens designs... would also explain why the larger element lens may sometimes perform worse than their smaller brethren perhaps.
It should be fairly easy for Canon to tweak the control circuitry to deliver larger voltages in bodies with larger power supplies to drive some of these lenses AF quicker... more voltage would spin the motor faster (assuming current holds up).
Very true, AC power involves some different dynamics, and can be more complicated. I'm decent with DC power, not as good with AC power.
Which begs the question....
Would you wear out a lens motor on a 1 series body; sooner than you would on a smaller body?
Good question. I figure it probably depends on the lens. The big white telephotos are built like tanks.
I accidentally dropped one from about 6 feet up when I had my camera slung over my shoulder on a tripod. It was my "heavy duty" tripod from about four years ago that had a removable center riser pole. I remove it whenever I use telephoto lenses. Sheath inside the tropod base cracked, apparently led to too much strain on the latch underneath the head that kept the whole entire assembly attached to the tripod legs...and my 7D with one of the new (rented!) supertelephoto lenses droped strait to the ground! I literally think my heart stopped for a moment when that happened, but it landed on ground that was partly covered in about 1" of snow, and relatively "soft" lightly damp earth and matted grass underneath.
The hit sounded really hard...but after some extensive testing....not a single thing seemed to be wrong! The lens was still tack sharp, focused instantly, the camera still operated perfectly...everything seemed to be ok. There wasn't even a scratch on either the lens or body...no dents, nothing. Everything was physically, electronically, and even mentally...in perfect shape.
(Suffice it to say, I no longer use that tripid...I locked it down as tight as possible that day, but I've moved on to a Gitzo GT3532LS now, which is just a phenomenal tripod!) So, I'd figure that Canons most expensive lenses can handle the power from a heavy duty body like the 1D X. It seems as though they have explicitly designed circuitry to provide better AF drive performance when attached to more powerful bodies than lesser bodies.
I am not sure that would be true about all Canon lenses, though. There are definitely lesser L-series lenses, and even though they are "professional grade", they are not quite the same build quality as the better lenses.