Sorry, guys, I really do understand how it works. I thought I was quite

That's why I said the l steppers 'drive' the carousel around. Notice the '
'. Yes, to spell it out.... the motion of the X-Y steppers in a circular
motion results in the carousel rotating. The carousel rotates as a result
of the XY stepper motion.......

The net result is that the carousel rotates while the nut is being loosened.
The motive force for this to occur is the stepper motors. The carousel
itself is passive.

This is a bad idea because;
- stiction can result in a much higher force to loosen the nut than tighten
- any lost steps in the stepper motors will result in a poor subsequent
trajectory, it will be fighting all the way
- there is no simple way to monitor the torque necessary, or applied.

So... instead of using the steppers to effect the required action of
loosening the nut, rather move... the motive force to the carousel.
Visually the result is the same, but since the carousel is now DRIVEN
instead of just coasting around, the benifits are;
- geared DC motors of the required torque are readily available, or use a
windscreen wiper motor with a further reduction
- the motor current is easy to monitor
- disable the stepper drives so the gantry becomes passive and is pulled
around instead
- indexing of the carousel only needs a single switch to home it.


On Thu, 18 Apr 2019 at 13:50, andy pugh <> wrote:

> On Thu, 18 Apr 2019 at 10:22, Roland Jollivet <>
> wrote:
> > To recap; small steppers 'drive' the carousel around to tighten the
> motor.
> No, the motor drives round the carousel to tighten the collet.
> It is really rather clever. Assuming that it can't work based purely
> on guess-work seems silly.
> I suggested a very simple test using the same torque wrench as Gene
> presumably uses now to tighten his collets to the correct torque to
> test the hypothesis.
> But, assuming a 5mm pitch screw and 5:1 motor reduction:
> (0.5 Nm stepper * (2 * pi) / 5mm ) * 5:1 = 3kN. On the end of a 75mm
> arm that is 235Nm.
> Correct torque for an ER20 is 75Nm.
> (Though I am not convinced that an ER17 can really lift a 300kg mass,
> so suspect I messed something up. )
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> — George Fitch, Atlanta Constitution Newspaper, 1916
> _______________________________________________
> Emc-users mailing list

Emc-users mailing list

Reply via email to