Servo driver selection

Gatesy wrote: So the output powers 2 windings, then as the motor rotates it moves round to the next winding, and so on. Is this like powering a 3 phase motor with single phase power where you rotate the single phase round the windings to simulate 3 phase?

Not quite.

The six steps are as-follows, where the three terminals (normally termed UVW) are either connected to positive voltage, negative voltage or no voltage.

UVW
0+-
-+0
-0+
0-+
+-0
+0-

Does the MESA 8I20 work the same way as it says this provides 3 phase power?

No, the 8i20 takes numeric input values on the serial link, the numbers represent commanded current and the motor rotor position. If the positions sent are the 6 steps of commutation (0, 60, 120, 180, 240, 300 degrees) then the output terminals will be driven like a 6-step drive, but normally in CNC applications you have an encoder on the motor, and can send a more accurate motor rotor position and get sinusoidal 3-phase drive.

That's great thanks, I can understand now!

Think I'm finally starting to understand a bit more now

So does the MESA drive take into account the rotational position of the motor whereas the PICO doesn't?

Does this mean that the MESA drive will give a smoother motion to the servo

Will driving the motor with the PICO drive (and the MESA??) mean that the motor will generate less power than when powered by the Fanuc drive?

Gatesy wrote: Does this mean that the MESA drive will give a smoother motion to the servo

Any sinusoidal drive will give smoother motion than a trapezoidal drive, but it isn't an enormous effect.

There is a demo here:

The difference is mainly the sound the motor makes.

This came up next, and looks helpful.

What output do the PICO drive and MESA drive give out? Is it trapezoidal or sinusoidal?

I see on the video the machine uses a MESA 7I39, I'm bit confused here as to what the difference is between a 7I39 and an 8I20??

One says brushless DC and the other says AC, but as commented in an earlier reply on here they are effectively the same thing?

Gatesy wrote: What output do the PICO drive and MESA drive give out? Is it trapezoidal or sinusoidal?

As far as I know the Pico drive output is trapezoidal. The 8i20 and 7i39 is whatever you tell it to do.

In the case of the 7i39 it takes three separate PWM signals, so can actually do weird stuff (deliberately or accidentally)