On Tuesday, August 09, 2011 02:33:30 AM Tobias Gogolin did opine:
> Thanks cogoman and Roland for replying, yes indeed that is a quite
> important explanation why they use such a ridicoluously low voltage
> high curent motor (even though they use very thin wires)
> Torchmate kit came with a 5V 7A motor with 6 wires each! I wonder what
> kind of circuit model uses 6 wires?
That is a unipolar motor where normally the motor supply voltage is
connected to a center tap on each winding, and transistors are connected to
the end wires. They are turned on to ground, but never at the same time.
> How many phases might this motor have?
The usual 2.
> Also just thinking about it now, isn't the real concern the positive
> capability to move the sleds to the position and never to miss a step?
Yes.
> What if I rather focused on the smart move to close the loop (put a
> digital readout on each motor) and this way make sure that i only go as
> fast as i can positively accelerate the sleds???
Unforch, generally this is made difficult by the fact that if the motor is
being told to move faster than it can and slips a step, which will be
detected, but the correction applied is to supply the step signals at an
even faster rate. Generally the motor stalls. :( You have to reach back
into the trajectory planner and slow the whole machine before issuing the
corrective step(s) to that motor, thereby keeping the rest of the machine
from exceeding the allowable error and stopping everything with a 'joint
error'. It may have been done, but tuning such a setup can reduce ones
hair follicle count. Drastically.
I found in my small machine, that the MAXVEL's could be doubled by
restricting the accelerations so they were rather leisurely. Mine carves
about as much wood as it does metal, using a die grinder as a 2nd spindle
to carve both the mortise and the tenon of a furniture joint. The aux
spindle is offset to the left and forward of the normal spindle so that the
stick getting a tenon carved on its end, clears the front of the table and
can hang clear to the floor in a fixture clamp I made.
So the fix is to never accelerate faster than the motor can move under
load. Resonance dampers on the motors can also help quite a bit, and you
will see many, usually home made versions of those as you tour the web and
you tube looking at other machines, they are hanging on the motors rear
shaft.
Similar remarks also favor 'microstepping' as this smooths the motors
motions by regulating the currents such that a 200 step/rev motor becomes a
400-800-1600 (or more) step motor. I am currently using 8 microsteps, but
I have new drivers on a rowboat from Hong Kong that claim they can do 64
steps. That may well be overkill, but it will be fun checking. And much
quieter in operation.
[...]
Cheers, gene
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Outside of a dog, a book is a man's best friend. Inside a dog it's too
dark to read.
-- Groucho Marx
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