Servo driver selection

Ok, so reading through the recent replies

So on Fanuc it sends 6 PWM signals to the 6 transistors (1 signal for each transistor) whereas on the PICO system it still has 6 transistors but 1 PWM signal is sent that then gets fed to the 6 transistors?

If the fanuc drives have 6 transistors and the PICO is a 6 step drive, is this the same thing? So if using a PICO drive on a Fanuc motors will it perform the same as if using a Fanuc drive?

Using the PICO system and having LinuxCNC compute the moves, to me this seems much more like a proper closed loop control system, rather than having other parts of the system computing things as well as LinuxCNC

Is there any advantage in sending the individual PWM signals to each transistor over just using 1 PWM signal, or was this just the way it was done at the time? Is it because technology has progressed that you can send 1 signal?

I'm guessing that like with everything the technology available now as compared to 30 years ago means you can do the same thing with far less components, and using the computer to do more of the processing?

Gatesy wrote:

Ok, so reading through the recent replies

So on Fanuc it sends 6 PWM signals to the 6 transistors (1 signal for each transistor) whereas on the PICO system it still has 6 transistors but 1 PWM signal is sent that then gets fed to the 6 transistors?

If the fanuc drives have 6 transistors and the PICO is a 6 step drive, is this the same thing? So if using a PICO drive on a Fanuc motors will it perform the same as if using a Fanuc drive?

No, not the same. With the original version of the red cap motors, Fanuc apparently used a scheme where they have 16 steps in a synthetic sine-wave drive, as commanded by the 4 commutation bits from the encoder. The later systems with serial encoders generated a true sine wave using angle information from the encoder.

Using the PICO system and having LinuxCNC compute the moves, to me this seems much more like a proper closed loop control system, rather than having other parts of the system computing things as well as LinuxCNC

Is there any advantage in sending the individual PWM signals to each transistor over just using 1 PWM signal, or was this just the way it was done at the time? Is it because technology has progressed that you can send 1 signal?

Well, the Fanuc scheme allows them to have current in all 3 windings of the motor at all times. The six step scheme only has current in two windings at any time, and there is a current discontinuity every time the commutation advances to the next coil.

I'm guessing that like with everything the technology available now as compared to 30 years ago means you can do the same thing with far less components, and using the computer to do more of the processing?

In general, yes, but the Pico Systems servo amp is decidedly "old school".

Jon

Thanks for the further info.

Sorry but I'm more of a mechanical person than electronic, so I'm almost keeping up!!

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?

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

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?

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?