Re: [CAD_CAM_EDM_DRO] Re: Video of my resonance

Dave,

Yes I will have to get a larger pinion, as it will be smoother. Actually it isn't too bad now. The main reason why I have used a smaller pinion rather than the proper larger sized pinion is so that I could make advantage of more reduction.

John,

Well, I disconnected the spring that has tensioned the pinion up to the rack. Then I disabled the slaved A motor in mach so that only the X motor was running.

Then I repeated the speed tests etc, the noise was much much louder with it just hanging loose in the air. Obviuosly the spring pulling tight to the rack some how cancels out some vibrations.

Then I done some more stuffing around and though to myself. When you first setup Mach, the set steps per unit number is 2000. I asume that this is a pretty common value for people who run ballscrews or similar with the higher gearing/reduction.

My steps per unit is only 68. So then I thought I would change that to 300. Then I ran a program at 68 steps per unit and then again at 300 steps per unit. What happend? .....The program running at 68 steps per unit still had lots of vibrations. But at 300 steps per unit, the vibrations disapeared. Then the motor sounded like some CNC milling machines that I have heard before, with that funny pitch changing sound.

This really does make me beleive that I need more reduction on my table. If I am using 68 steps per unit and that is with 10x microstepping. That is only 6.8 steps per mm, compared to the one at 30 steps per unit or the 2000 steps per unit which equate to 200 steps per mm with out microstepping.

I'm 99% sure that all it, is is the motor spinning so slow that every step in the motor is felt. When you turn the motor shaft by hand, you can feel the steps in the motor as well. I really think that I need more reduction.

I'm going to post a question on the mach yahoo forum asking if anyone else has the larger 34 sized motors and what their steps per unit is set to. Then I will see if I can get someone to change it to 68 steps per unit, and move their machine slow to see if they get the same results.

Peter
Australia

----- Original Message -----
From: John Dammeyer
To: CAD_CAM_EDM_DRO@yahoogroups.com
Sent: Monday, September 25, 2006 7:20 PM
Subject: RE: [CAD_CAM_EDM_DRO] Re: Video of my resonance


Hi Dave,

Just one thing about your process below. If indeed the resonance is like
the twin engine beat (or two almost in tune instruments), then just
loosening and retightening might not do it. What I'm thinking is that if,
at their rest position the first step energizes different windings, they
motors could still be out of sync although now not by micro-steps so perhaps
it's not an issue?

But, depending on how his hardware is configured, does one motor turn
clockwise and one counter clockwise? What I'd try for, is to ensure that
each motor energizes the same winding from that 'rest' position you describe
below and that the motor moves in the correct direction when those windings
are energized.

Again, perhaps that's not needed. Might well just be a micro-step out of
sequence issue. Normally the beating of the two out of sync propellers
comes from one engine running at a slightly different speed. Just like an
analogue mixer in radio, what we here is the sum and the difference of the
two frequencies.

One way to find out, if it's mechanically possible is for him to disconnect
and decouple one of the two motors. Since the gantry is on a track and not
running a double worm, one motor might be able to move the works at the slow
resonant speed.

Just more ideas. Perhaps I'm way off too.

John Dammeyer

> As for the out of sync, that would be simple to handle.
>
> I think you could just power off everything (lock the table to keep it
> in posistion.
>
> Loosen the motor pulleys so the motors can move easily.
>
> Then tighten the pulleys again.
>
> That should have the motors cog into a natural posistion.
>
> If the tightening of the pulley moves something, then it may go out of
> sync.
>
> I could be wrong, so comments are welcomed.
>
> Dave






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