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run the motor at slow speed, and measure the signal using an oscilloscope with an inductive probe. It will show DC/AC, and if the waveform is PWM or not.
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Ok, so it's just a REAL little thing on my PM-1228 lathe...
- Thread starter Tired&Retired
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easy if you have an oscilloscope.. Any other way?
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probably. it is the only way I know to be absolutely sure. I'm not much of an electron-head. purely a dabbler in it....
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The term DC brushless is a total misnomer- it's a 3-phase AC motor with a permanent magnet rotor
DC motor usually refers to (and should be reserved for) a brushed motor
-M
DC motor usually refers to (and should be reserved for) a brushed motor
-M
I do not know a great deal about motors, but I don't really think that brushes are necessary for a DC motor. As you say you can have AC motors with a permanent magnet rotor, but ... Permanent magnet DC motors do not have to have brushes. The commutator does not have to be mechanical. For example, if the permanent magnets are rotating their location (field) can be sensed by magnetic field sensors (such as Hall effect devices) to communicate with the power drive, which drive the non-moving coils. Nothing says this has to be 3-phase. Just depends upon how many coils there are and how many permanent magnet poles. Once, you have the electronics they can also ajust for speed and phase and hence improve the torque vs speed curve when under load. By the way, the permanent magnets can either be on the inside or the outside, but to avoid brushes, the coils should not be moving. Stepper motors have lots of poles (typically ~ 200, small steps) and the coils are driven, but in most simple motors there is no feed back as to the phase between the coil and the magnets. They are also full of iron to carry and focus the magnetic flux at the poles. The iron causes cogging where the rotor iron tend to align to the pole and prevent the motor from turning when there is no power (This can be good or bad, depending upon how it is used). There are also similar designs where there is no iron interacting with the coils, just coils and magnets. These do not cog and can have considerable torque and speed. An angular segment of a motor (two poles and two coils) of these are used in the Hard disk drive head arm actuators, which needs to move the recording head very rapidly across a disk surface (inches) and be able to be positioned very accurately by the final "DC" current. ("DC" in quotes because these actuators are essentially starting and stopping all of the time, but once they have reached the desired magnetic recording track, must be servo-ed by smaller currents to stay positioned the tiny track ... which is less than 0.1 micron in width.)
By the way, wrt motors and power, a great book to read is "George Westinghouse: Powering the World" by William R Huber. It gives a little information about motors, but more importantly it describes the early days of electricity distribution and use.
Book Report: Westinghouse and Edison were in competition for most of their lives. We all know about Edison, largely because he was a self promoter, and while we know the Westinghouse name the story of Westinghouse's life is not so well known. Unlike Edison, in simple terms, Westinghouse was a nice person, and took care of his employees. Even encouraging them to invent things and then own the patents and resulting businesses. He also helped them to get educated. It seems that Edison had to have his name on every patent whether he really invented the work or not. Powering the World is largely about the rivalry between AC and DC power distribution. Because of resistive losses and the required high currents of the DC systems (low voltage) they could not convey power very far, requiring generators every few miles. Westinghouse's systems won out, largely due to the distances between generators, but it is an interesting story about getting there. Tesla was all about AC electricity and designed motors, transformer, etc that was essential to the power grid of today and went into Westinghouse's systems. His up and down converting transformers are essential. He went to work for Westinghouse. Of course Westinghouse made most of his money and reputation on mechanical systems and control systems. These significantly reduce death and injury of both rail workers (breakmen) and passengers. His Air Brake systems for trains are still used today. Along with many other important inventions, he invented train rail switches and the re-railer for getting rail road cars back on the tracks.
If I recall, some of Westinghouse's bigger generator systems had the rotor on the outside.
Dave L.
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Yes I stand corrected, the commutator does not have to be mechanical
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I would actually be more interested in verifying the power rating of the motor.
But back to the ID label I am working on, I tried it with an aluminum plate. First I cleaned the surface with a full scan of the laser at full power/high speed to make it an off white color. Then multiple passes at a slower speed at full power to engrave and darken the image. Didn't warp the aluminum plate at all, and this is much easier to read at multiple angles than the polished stainless steel surface. I may do another one, but bevel the edges of the plate a bit first. Maybe not so deep on the engraving, neither.
Attachments
Your label looks pretty nice!
However, I am a little surprised you are getting much of an engraving process at all. Metals, SS and Al, are pretty reflective at this wavelength. You need a wavelength that is absorbed by the substrate material. For metals this is typically in the blue or UV (<~ 400-450nm nm = 0.4 micron), not the infrared (1064nm = 1.064 micron). However Nd:YAG solid state lasers (also 1064 so the fiber probably has the same or similar material in it) have been used for many years, before the Fiber lasers for resurfacing. However, it is not uncommon to frequency double or quadruple the YAG laser frequency to get them down in to the green or UV wavelengths for better absorption. Since the light that reflects off of Al or SS is pretty color free it indicates that it is not absorbing at the visible wavelengths much at all. Once you have an absorbing wavelength and sufficient power densities, then the metal surface will ablate off rather than just heating to metal ... or to react with the oxygen/water/or what ever else is in the air at the surface. They sometimes "cut" metals with really powerful, big CO2 lasers (~10 micron wavelength), but they are always flooding the surface with O2... so the melted metal is oxidizing fast and being blasted a way. The 10 micron wavelength is pretty good at being absorbed by water and this is why they use the CO2 in wood (carvings) and for cutting many layers of fabric at one time.
The Al is a much better conductor than SS and so when you heat it locally the heat is being distributed over the metal better than it is when the surface of SS is heated. Uniform heating means the substrate is less likely to warp. So maybe you are seeing this. Warping implies you have induce stress in the surface. Depending upon the curvature, the laser process surface is either expanded or contracted. I ran in to a similar warping when I machined the surface off of a sheet of Al to make the sheet thinner. I then clamped it flat and put it in an oven for a few hours to relieve the stress. It then came out flat.
You could paint the surface and then run the laser over the surface to remove or react the paint and get the pattern. However, how durable is the paint that is left behind. I have never done it by my understanding is that SS surface can be made black by oxidizing it to the proper FeOx state, i.e. Fe2O3 vs Fe3O4. To do so I think you take it to a very high (glowing red) temperature and then plunge it into an organic coolant (oil) which probably breaks down and reacts with the surface. This surface you could then probably treat it as though it had been painted on. However, once again this oxides is probably thin and may wear.
By the way, copper and bronze are somewhat red/orange telling us that this material reflects in the red/orange wavelengths (and near IR) and absorbs in the blue green wavelengths.
Your fiber laser is pulsed and the time interval between pulses is probably much longer than the actual pulse length. This means that the the instantaneous power level is probably much higher than the power rating, which is usually the average power. Assuming that the pulse length is 0.1 microsecond and that the rep rate is 100,000 pulse per second ( 10 microseconds between pulses) this means a duty factor of 0.1/10 or 0.01. Hence the peak power should be 100 times the average power. This helps to make fast reactions occur but if it boils down to just heating the metal and then having react with the air, the diffusion of the heat away from the spot can become dominate. In your U-tube video the laser light was causing flash of light so there is some sort of reaction occurring.
It all kind of makes me wonder what you would get if you were to mist the SS with a bit of oil (carbon and oxygen source) while you were running the laser. It is probably messy and may screw up your optics?
If there is any interest, take a look at the following patents where the surface of hard disk substrates were laser processed to produce a long wear (low friction) surface. Since that time folks have use similar processes for many other applications including reduced wear in human artificial joint surfaces.
US5062021A - Selectively textured magnetic recording media - Google Patents
Magnetic recording media are controllably textured, particularly over areas designated for contact with data transducing heads. In connection with rigid media, the process includes polishing an aluminum nickel-phosphorous substrate to a specular finish, then rotating the disc while directing...
patents.google.com
US5108781A - Process for manufacturing selectively textured magnetic recording media - Google Patents
Magnetic recording media are controllably textured, particularly over areas designated for contact with data transducing heads. In connection with rigid media, the process includes polishing an aluminum nickel-phosphorous substrate to a specular finish, then rotating the disc while directing...
patents.google.com
Dave L.
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OK, finally got something I liked enough to actually mount on my lathe. Unless I think of something else later on, of course. 
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Looks great! Wanna make me one for my Atlas? LOL