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ServoDatabase lists various different servo motors, and describes some as "analog" (e.g. SG90) and some as "digital" (SG92R).

"Digital" servo motors are apparently better (they seem to cost more, anyway).

I've read a number of sources that dismiss the label as "marketing". Even if there is an actual technical difference, what could I check in the devices' specifications sheets that would confirm that motors described as "digital" do indeed enjoy those technical advantages?

  • What is the difference between "analog" and "digital" servos?
  • What difference should this make to me when I am using them - can for example SG92R motors simply be treated as drop-in replacements for SG90 motors in the same sort of application?
  • When I'm driving them (directly from the GPIO pins of a Raspberry Pi) should I treat them any differently - for example, if I have been using a 50Hz pulse to drive them, should I change this or any other parameters for a digital servo?
  • Are digital servos more or less easily damaged (by excess load, electrical errors, etc) than analog servos?
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    \$\begingroup\$ A Google search will give you the answer in a few seconds. Question should be closed - insufficient research. \$\endgroup\$ – Leon Heller Mar 6 at 16:29
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    \$\begingroup\$ "Digital" uses the same pulse width modulation as an input signal, but puts a microprocessor in the servo amplifier instead of the old analog pulse stretcher. \$\endgroup\$ – TimWescott Mar 6 at 16:30
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    \$\begingroup\$ @LeonHeller I indeed found a lot of information - unclear, sometimes out of date, sometimes tendentious and often contradictory. That's why I am asking here. You may already have the knowledge to separate unhelpful or incorrect information from what's useful, but I don't. \$\endgroup\$ – Daniele Procida Mar 6 at 16:54
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In RC modeling parlance, an "analog" servo uses an older technology analog servo amplifier (amplifier = controller in this terminology). A "digital" servo uses a servo amplifier with a microprocessor in it. Digital servos tend to have more torque and shorter response times for the same motor and mechanical assembly.

(Note that there's no fundamental reason you couldn't build a super-hot analog controller; it was just never done, and would have been much harder to stuff inside an RC servo case, so the world had to wait for itty bitty microprocessors).

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In addition to the answer provided by Tim Westcott I can add some additional information to answer my own questions:

The internal difference is the microprocessor that controls the motor. This has some implications for its use.

What difference should this make in practice?

Can for example SG92R motors simply be treated as drop-in replacements for SG90 motors in the same sort of application?

A digital motor cannot simply be dropped in as a replacement for an analog motor; depending on the application, it may behave very differently.

An analog motor has a much greater apparent dead spot around its current position. One consequence of this is to provide an built-in dampening effect. A digital motor is much more sensitive to small movements away from its current position, and will correct much more rapidly.

If the mechanism it's controlling is itself undamped, this can lead to violent oscillation as the servo's own movements repeatedly overshoot and undershoot the correct position.

In a mechanism where the movements of two motors are at work and interact, the slightest movement can result in uncontrollable behaviour.

Should they be driven differently?

When I'm driving them (directly from the GPIO pins of a Raspberry Pi) should I treat them any differently - for example, if I have been using a 50Hz pulse to drive them, should I change this or any other parameters for a digital servo?

In my tests I didn't see any difference in when controlling a digital motor using 50Hz or faster pulses, so as far as I was able to ascertain, they can be driven by the same pulse regime as analog motors.

Are digital servos more or less easily damaged than analog servos?

( i.e. by excess load, electrical errors, etc)?

I haven't been able to discover either in testing or research any clear difference in their ability to withstand mistreatment.

Several of the analog motors I tested simply stopped working and none of the digital motors, but it's not possible to say why.

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  • \$\begingroup\$ That's a rather dubious claim, are you sure you are talking about RC hobby servos? The digital ones are in fact designed to be a direct replacement. There are other long known issues such as aeroelastic flutter, but as servos tend to be much stiffer than what they are connected to, the situation you are describing does not seem something likely to occur in intended usage. Further, there is absolutely no reason why a digital servo amp cannot have the exact same behavior as an analog one. \$\endgroup\$ – Chris Stratton May 10 at 2:18
  • \$\begingroup\$ @ChrisStratton What I described is easily observed and reproduced with multiple devices. Yes, all hobby servos; in fact mainly the SG90s and SG92Rs I mentioned in the question. \$\endgroup\$ – Daniele Procida May 10 at 7:35

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