On 1/21/23 20:20, Robin Szemeti via Emc-users wrote:
That looks like a useful module ... sine for one of the coils, cosine for
the other, and simply multiply the cosine signal by the servo drive signal
+1 goes one direction, -1 goes the other and anything in between is just
slower ...
I have a company that manufactures audio amps, driver stages won't be a
problem.
Just got to do some testing of the resolvers and decide which version of
the Mesa hard to order, I think these resolvers output 2 x the input
voltage, so I probably need the HV version, but we'll see.
This will be used on the 10GHz band, with about 400W from a travelling wave
tube .... there are good Python modules for moon position data, 'skyfield'
is the best of the bunch, I need roughly +- 1 degree precision, with just a
position update every 30 seconds or so .. the move doesnt move that fast. A
good resolver should easily be able to get within 0.5 degrees ...
I'll let you know how it pans out.
One of the reasons I mentioned the stepper/servo is that with its
builtin encoder telling it where it is, the error signal is then used as
the current control to the motor. It gives two characteristics to the
control, the first being its accuracy in terms of rotational precision
can be just one or two counts of the encoder, which in even the bargain
basement models has about 14 bits of resolution per full turn of the
motors armature. Such is the tech today, where a nema17 motor with a42
mm thick core, develops nominally .5NM at a max rpm of about 1000,
drives with the normal step/dir signals,and sells for about $40 a copy
on amazon. Needs 24 to 28 volts, and about 2 amps when working hard,
microsteps to 256, we normally run them at 16, meaning 16 steps either
way are one full steps move. That $5 arduino can drive them. They would
need weather protection, but what doesn't. First stage geardown would be
a 20 tooth gt2 pulley and 6mm wide belt turning a 150mm diameter pulley,
which would drive another chain drive with #35 chain. Big 3 layers of
plywood for the final pulley. Or drive the screw in a long sat jack
from Venture mfg in Dayton OH, but that would involve correcting for the
non-linearity, and a full 180 scan is at best impractical.
The other just as huge advantage is if it hits a stop and can't get to a
+-2 counts or so balance between where it was told to go vs where it is,
and if that is violated for any great amount of time, it will close a
circuit, stopping linuxcnc in its tracks. I can on my 11x54" 80 yo
sheldon lathe, position a jaw so the tool chip will hit the jaw, issue a
move at an 1nch a second causing the tool's chip to hit the chuck jaw,
It runs to hit the jaw, see's the stop, and kills linuxcnc in about a
millisecond. The carbide chip in the tool is not damaged, nor is the
chuck jaw marked.
The mks-servo42C OTOH will blow its drivers if it can't get there.
Yet that has never actually happened while doing real work. The original
2 phase steppers, they ran at a constant current when moving and half
current standing still so they ran just short of burn your hand hot.
Now these run maybe 10F above ambient unless working really hard at high
speeds, a considerable power savings.
[snip]
Take care & stay well, Robin.
Cheers, Gene Heskett.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>
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