Hi Group,

I have this RC airplane hobby which fr I use servos for operating the
control surfaces and the engine speed.

Recently I have decided to buy my first digital servos, which is much
smaller than the old traditional one, however, has the same torque with
faster speed to move the arms. In fact, with an analogue one I can move the
arms slightly out of it's position while it was nearly impossible with the
digital one.

Anyway, I have read that the digital one takes more power and drains down
the battery quicker, so I have started to do some measurements to see if
this true as it did not make any sense (same torque needs same input power,
right?). As a results it turned out that while at 'no load idle' the
digital one requires 2/3rd less power, however, on full power a traditional
Futaba 3003 takes about 600mA (I tried to push the arm out of the desired
position), the digital one take about 1A (so almost twice as much). My best
guess is the excess of power is needed to hold the arms tightly in
position. Question about this as follows:

- How to calculate required power for electromechanical components like
this? So if they say the torque is 3.5 kg / 1 cm arm length for both
analogue and digital, but the analogue gets out of the way by x degrees on
full stress, can you calculate from this the required power?

- Can we actually explain the excess of power in need with this behavior?
(how tightly holds the arms at full power)

- Do you think I would need to make a data acquisition device to see how
much power it takes or is it enough to measure the charge of the battery
somehow and the time spent in the air to be able to tell it in a less
accurate way and make some calculations as well?

Many thanks,
Tamas

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