3D printing Widgets

OK, the mechanics are the same but the analogue ones work on a 50Hz Pulse Width Modulated signal, the digital ones on a 500Hz one presumabley with some sort of coding.
It could be Binary or a Gray code or something similar.

Looking on the Aliexpress site the two are confused on several suppliers, there is an analogue one pictured & the description say digital. As I've said with AI (joke)  its Caveat Emptor.

I've reorderedfrom a different supplier within AI, slightly dearer, £14.95 for 4.

 

The servos all have the same mechanics and electronics, so should work with your ordinary receiver.
The digital ones (if they are) draw more current, but the centreing is more precise, and you might hear them buzzing gently when not moving - that's the motor making micro-adjustments to hold the servo in the spot.

The analog servo derives a voltage from a potentiometer under the output shaft, that voltage feeds one side of a comparator, the received channel feed is converted to another voltage which is fed into the other input of the comparator, the resulting output drives the servo motor. when the voltages are close to equal the motor stops. Digital is similar in that the output shaft signal goes into an AtoD converter and the digital output from the RF side is used to compare the output from the converter, much more accurate but can result in more current usage when the servo is in position

On our machine tools the leadscrews originally had a resolver which fed back a rotary phased signal but with the advent of microprocessors they went to digital encoders.
I suppose on RC servo scale, to produce such a small encoder would be difficult/expensive.

Any way it doesn't sound as if they are compatible.

It's worth plugging one in and seeing what happens.

I'm going to return it, they might not like it if its smoking!

O ye of little faith!, you could try a servo tester.

Klippy has it correct, they will work regardless of being digital.

I have been trawling the internet to try & find a definitive answer or explanation.
The word "Digital" meant to me that the signal from the receiver to the servo is coded, it could even be Morse Code.
However this is not what it means. It seems that the "Digital" refers to the control board inside the servo. This operates at a higher frequency of 500Hz & uses digital circuitry. Obviously someone has labelled them "Digital" to hype them up and confuse me. The signal from the receiver to the servo is still PWM, it just means that the servo can handle frequencies anywhere between 50 & 500.

Way back in 1970 I worked on a "Light Link" which used fibre optic to carry a signal from high voltage switchgear to ground level. This used a 1MHz carrier signal & it wasn't digital. It used a low-pass filter to get the required signal voltage.

I fear you are over thinking the use of the word "digital"
However to operate a servo from a digital encoded signal would require the receiver to send such signal.
It would thus create a new standard making all previous servos and receivers incompatible!
 

I thought such receivers did, thats why I couldn't understand how they could be compatible.
A digital radio wouldn't work with an AM signal!

Magpie - you are mixing different types of data transmission!
Very simplistically - 
AM - Amplitude Modulation - is a form of transmission where the centre frequency is fixed, but the required info is sent in a way that the volume goes up and down without changing the frequency..
FM - Frequency modulation - is a form of  transmission where the bandwidth is fixed between two limits, but the radio frequency wiggles about inside that bandwidth.
Digital - DAB - is very different, and is a way of transmitting many different signals on a fixed frequency - via an encoder, (multiplexed) and the receiver has the matching decoder that can sort out the different streams.
Digital as far as WE are concerned is a sequence of ons and offs, sent in a chain, with a reset tone at set intervals. A sort of DAB without the A (audio) bit. (Morse code, that you mentioned, is a sequence of ons and offs, sent in a pattern that translates to letters of the alphabet if you know how to read it - I do). The digital for radio control spans a time of a few milliseconds between resets, and is composed of a positional data-burst for each channel the transmitter can use, sent in a fixed sequence, ie channel 1 goes here, channel 2 goes there - and so on.
The PWM - pulse width modulation is how long the on is, compared with how long the off is - stepping around the (reset) 1, 2, 3, etc. That tells which servo which way to move, and how far - until the transmitted and the servo generated  signals match. The 'digital' in a servo is just another way of the servo deciding where to move, via a PWM converter.
You would have to look at the unprocessed (before it separates the 1, 2, 3 etc) output of the receiver on an oscilloscope - to see the various channels puttng out the wave-form. If you have an audio receiver that can tune the frequency, you will hear a burring noise, and as you move the tx sticks, you will hear variations in the tones that match the stick movements.

This is why one brand of transmitter will not operate a different brand of receiver - if you like, they are talking different languages.
I won't go into multi-mode here, but it is similar to someone being fluent in several languages, so can be understood.

I know all that.
My point is that they slapped the word "digital" on it when it was only some of the internal electronics that were changed to digital. Calling it digital implied to me (and others) that the whole animal was digital including the signal from the receiver. I have never seen it plainly stated that the signal is still PWM.
I know its alot to expect of Aliexpress but I said on my return note that it wasn't compatible with my receiver, there was no response to say it was.
Being a recent returnee to the hobby the thing that struck me was a total lack of standardisation.

The fact that you can take any servo with a plug that fits and plug it into any receiver, to me = standardisation.

The fact that different manufacturers have different communication protocols, even between items in their range indicates to me that the respective manufacturer is interested in improving the breed.
Much of the diversification has occurred since the advent of 2.4ghz, because it is so versatile. I don't understand how people managed to go flying every weekend using 29meg, 35meg et al, but they did, even though they risked getting shot down every time they flew.
 

With modern gear, the part with the highest failure rate is the muppet holding the transmitter!