Re: A Modest Proposal!

Jon Elson wrote:

> KalleP wrote:
> > However servo motor feedback loops may be something to consider in terms of CPU resources and RTOS latency.
> Actually, servos are easier to control. While steppers need microsecond
> timing of step
> pulses, a servo might need to be updated only every millisecond. Of
> course, the
> servo needs some external hardware to create the velocity command to the
> drive.

Hmm, interesting I lean something new every day.

I assumed the basis for cheap servo operation in DIY CNC was handed over to the CAM software totally. If this had been the case then the CAM would have to handle the encoder sampling which could be quite high with large line counts. If the encoder feedback and velocity management is synchronised somehow with hardware to let you do actual point to point multi axis translation then servos drives certainly have a huge point in their favour with any platform. I have some nice low inertial motors left over from 9-track tape streamer capstan drives that were made for fast moves (they even have a forced air cooling fitting) that are crying out for servo use.

I was also under the impression that with reasonable micro stepping some small timing jitter would be mostly averaged out on the moves (even multi axis interpolation) due to the inertia of the system. Obviously it will start to generate some weird noises if the steps were to have an uneven clocking, I would guess that accuracy would not suffer much but may be wrong here as well.

While I have used all sorts of OEM and consumer XY equipment I have yet to complete any of my own CNC project but they are getting there.

Kalle
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Johannesburg, South Africa