Yes, Kevin your post came through. I'm with you on the laminated steel cores, but differ in that I think there is enough improvement to be worth the pursuit. Other than that, I'm still not quite sure how a thread on flux got off into invention and engineers, but I don't regret it. It seems like not knowing where things are headed can make for interesting conversations.
But to get back to the original question, I think we were discussing whether a the working gap in a magnetic circuit would benefit more from doing more work on the geometry and material of the core.....or whether the flux density in the gap (the gap being where the coil is inserted) would be improved more if we replaced a portion of the core with additional magnets.
Stated that way, my best first guess was that we are better off working on the core itself, as one of the weird things about magnets is that they don't conduct additional flux very well. But I hedged by saying that this is exactly the kind of nasty and debatable design problem that is easily resolved today with computer modeling. No technical skill needed, just a couple of hours with a free magnetic FEA program like FEMM will give a anyone a real answer to the kind of problem that used to require several day's work by someone with a serious magnetic education.
And then we kinda got off onto other things.
enjoy, Roger L.
----- Original Message -----From: Kevin PembertonSent: Monday, January 07, 2013 9:52 AMSubject: Re: [Electric Boats] Magnetic Circuits & The Prototype MotorsHi Roger,
Although I went to the groups page to unsubscribe seems I didn't do the job right. It allowed me the opportunity to see this thread. So I respond and stay with the list till those that want to respond to my comment have that chance. Of course this effort may be in vain because I don't know if I can still post to the group.
Roger all people are in fact classified. They are either classified as ambitious or as a slacker of sorts. It is best to simply state that an engineer may be an inventor but it is more likely he is not, he is an engineer. An inventor has set the standard for vision and drive above that of most engineers. In fact his lab is likely full of engineers of all levels that do the work of developing of the inventors vision, by request of the inventor, whom manages the team from some top tear. The inventor need not be an engineer but it helps him if he understands the language of his team. The level of managers that remove the inventor from the team is based on his understanding this language. If he does not speak the lingo he/she will need to have translators to instruct the engineer.
Either way it is important to understand that the number of disciplines required to engineer a motor requires many hats. This discussion will illustrate that point for me. For the person that asked about anyone thinking of using aluminium or other metal as the core on a motor should have had the answer "Yes". This would best be described by example. Voice coils(a motor) are used to run the head of many hard drives as well as speakers to a beat or to the location on the hard drive to retrieve or write data. The speed the motor reacts is based on the amount, if any, of steel used in the motor so in many cases it is not used. My use of the term steel in place of iron was intentional as the properties of the mix(alloy) determines the magnetic properties of the core. Not using a metal core is used for fast acting servos and motors but not in applications such as the traction motors we need to use in a boat.
The core of the motor serves as a flux guide nothing more. if we guide the magnetic flux we can obtain more work thus increasing efficiency over an air core depending on intended use. The more flux that makes it to it's intended location, the more work. This tunnelling has a disadvantage. When we turn the winding on we first must overcome the resistance of the core to charge or change as it were(overcoming this resistance is lost energy). The size of coil and energy required to overcome this resistance is higher than would be needed if we could use an air core for the job. As I have stated in the past all things built have compromises. When the core becomes fully charged we say the core is saturated. The better we control the power to the coil, the lower the temperature of the coil after the core is saturated, and we no longer need to overcome it's resistance.
What we use for a core depends on the speed we want the motor to react. Modern transformer laminate allows transformers to achieve 98% efficiency. The higher the count of laminates per measure, the lower the eddy current and higher the efficiency because this one loss is reduced. In all honesty? The efficiency of the modern motor is quite an accomplishment. This modern efficiency was not however spurred by the motor industry. Competition spurred keeping things as they were rather than efficiency. It was government mandate that changed the way motors were being built. Now that the ball is rolling, and the customer has come to demand efficiency, competition has been developed in better design.
I feel that Hall effect cogging and controllers that take advantage of such feed back are likely to save more energy in DC motors than further development of cores within the motor. Modern engineering practice is to design using off the shelf black boxes. Anything other than that is to re-invent the wheel. pun intended. Consider that a Prop is most efficient when positioned parallel to the boats motion. A prop with the least number of blades is most efficient because it lowers drag(making the number of poles low if a wheel motor were developed). Attachment of a nozzle to the prop blades so more poles could be incorporated in such a motor has proven inefficient and is also one of the reasons a Kort nozzle is not attached to the prop. Magnetic sludge I had not thought of, but this is just another reason not to re-invent. Wheel motors are large Diameter and would increase the angle of the prop to the horizon if gearing were not used. As stated earlier this would have a negative effect on overall efficiency of the design.
If I were to prototype a motor. I would likely incorporate a bulb on the front of the boat that contained the motor. This design I would take from the cargo ships as it has saved many barrels of fuel. From this bulb I would extend the prop shaft aft only enough to reduce the turbulence from the bulb. I would encase the shaft to reduce resistance from the shaft turning in the water. I would pressurize the bulb to keep water out of shaft and motor housing as is done on ROVs. The motor would be a wheel motor with control scavenged from a floppy or hard drive modified for the power requirements of a larger traction motor. This would allow for timing of power based on rotor angle, thus saving the need for brush maintenance, and offer pulse timing based on rotor location. The bulb would allow for proper positioning of the prop to the horizon, and the prop I would placed within a Kort nozzle. Torsional strength would still be required over a larger area of the boat and ballast would need to be added to overcome the weight in the front of the boat. Higher voltages would be used to overcome conductor length needed for motor placement and batteries would likely be the above required ballast. If one were to design a stringer for the required torque requirements they may be able to incorporate a battery box within it.
Anyhow it is better to design considering how much gain can be obtained with each component in the completed project. Some parts of a motor/control system should be improved for efficiency. combining the two items in seamless harmony would be the best advancement. Hull design to improve the dynamics of the drive system would make big strides in electric drives. Low maintenance motor design would make access to maintain the motor less of an issue. Our problem is we don't look at boats as one unit, but many.
There got it off my chest.
Kevin Pemberton
P.S. My apologies go out to anyone that could not find the unsubscribe link at the bottom of list emailings. Sometime during the course of scanning all posts, I found it easier to drop the HTML formatting(I chose straight text). I had not paid attention to the fact that doing so dropped those links from the page. If you are wanting those links in the future, and you have turned off HTML formatting, just turn it back on and the links will re-appear.
On 01/06/2013 08:10 AM, Roger L wrote:It's interesting that you should bring up professional accreditation. Many schools are accredited, but there is another level..... The national exams for a person to be an professional engineer - a PE - are still a true test of ability. That will be slower to change. Professional tests are heavy into theory, math, and hand-worked solutions. So far I can't see that a computer technology based education stands a chance of teaching the depth of knowledge required to pass those professional tests. And if someone can, then good for them.And frankly most of what is now seen as engineering work doesn't require that level of expertise. All it needs is a good background in basic science and a good modeling program. The good modeling programs give the modeler control over the materials and geometry while the program does all the calculations of things like current flow and interacting fields - and automatically includes the higher education stuff like eddy currents and edge effects that used to be mind-numbing to calculate. That's been a game-changer.I'm guessing we will see engineering break into different levels much like the medical profession has done recently.Roger L.From: Myles TweteSent: Saturday, January 05, 2013 11:51 AMSubject: RE: [Electric Boats] Magnetic Circuits & The Prototype MotorsSo it's both: The educational system moving away from student/instructor interactions combined with the student's unwillingness to put in enough time to be sure to learn the fundamentals. And given that online courses allow students to submit all work electronically, there's absolutely no assurance that the student did ANY OF THE WORK that was submitted. Accreditation organizations should pay attention to this...MT
-- Committing murder in exchange for lifestyle makes you a "thug" not a "Rights Activist"
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