Advanced robotics

Martin, The enabling factor is the distance, not how much iron. And this isn't like a sprocket and stepper. Magnetic fields are a >>product<<
of the two fields at a distance. Reduce the distance, boost the fields, and you get the power needed.
The real trick was finding a material to work. It was a, "gee, all we need is a ribbon 1/1000th of an inch thick, 1/2 inch wide, near zero stretch modulus, able to withstand high temperatures, wear resistant, and can hold 1/2 a ton." It was more like SciFi than science.
I fried a lot of stuff trying to get this to work.
Bruce

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You don't understand. For any given distance, the magnetic field strenght you are going to develop will be limited by iron. The second limit is operating tempreature (heating). You can use the best neodymium magnets if you want, but, if you don't have anything to carry that flux you are not going to produce decent results.
The energy equation for what you are proposing doesn't look good. I wish I had the time to do a real analysis. I can't, I've got a big project I'm busy with. But, just from experience, I just don't see how you are going to beat a good PMDC motor with gears in terms of efficiency. For every step you'll have to expend energy compressing and/or expanding springs.
Which leads to a question: Have you done the basic Physics 101 analysis of this thing? You need to show that to people in order to show some merit. The contraption can be made to move, of course, but, is it worth spending any time on it? That can be seen from basic principles.
There's also this business of kevlar in the airgap, which is not a good idea at all. There are better ways to do it. You do not want nor need kevlar in the airgap. Bad idea.
And, why do you need a pair of coils to clamp/move? One is enough. In fact, the whole contraption can probably be made with just two coils, not three.
Of course, the smaller the stepper motor's motion the worst your problems might become. At that scale things might bend and stretch in magnitudes significantly proportional to the mechanics of the motion itself. There's also thermal behavior to consider.
You need to put some Physics/Math on paper and see what you've got.
-Martin

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Martin, Yes, I have done the math. I have done the real world work (much more enlightening). I have tried other ways. This is best I have.
Not everything is about iron. It is about field lines, force, and most, most, most importantly scale.
Pick another material, besides kevlar that can handle the requirements (don't even go down the carbon fiber path please...been there). Tell us a better way. If you think it is a bad idea, then improve it.
Bruce

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Sorry Bruce, you are loosing me. You need to explain to me, in no uncertain terms, how it is that you intend to produce significant force electromagnetically without closing the magnetic circuit and doing so with the right amount of iron? It's like saying that you are going to make current flow without wires. Last time I checked, the laws of physics apply to everyone.
Regarding kevlar in the gap. I said it in my prior post: Terrible idea. You do not put anything in the gap for best force/results/efficiency/etc. You need to come-up with a better way to do it. I'll continue to argue that conventionally constructed DC motors will be more powerful, reliable and efficient than your tape-sliding stepping-motor.
--
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Martin Euredjian
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Martin, First, I appreciate your argument. I was there myself. I agree there should be something better...but until then. ;o) Also I love the "tape-sliding stepping-motor"...The sliding tape is very important to the mechanics...keeps things from breaking.
When the additional mechanics are added to move the kevlar ribbon from the magnetic gap, you increase weight as well as other complications. Since you have the coil separate, now you need a frame and a mechanism to squeeze the ribbon external to the coil. The mechanism will have a certain amount of flex which will increase the travel required and reduce the force that could be exerted.
The ribbon must be very, very thin because the magnetic field force falls off at a rate of a square of the distance. This also dictates that the range of motion must also be very small.
The step range is huge in magnetic terms for a stepper motor. Take a good stepper like a double stack NEMA 34 from PacSci. Each time a step is made, the rotor travels ~0.016 inches at the circumferance (actually, it is much bigger than that because there is an air gap between the magnet and lamenated ferrite). Now, the magnetic field must be strong enough to turn the rotor at that distance. In addition, the rotor contains many magnets, several coils, and the shaft/rotar. Plus, there needs to be a tremendous amount of material to guide the field lines to handle the multiple path they must follow.
Now, steppers are great (personally, very partial to API Motion which is now owned by PacSci). They can apply force to "absolute" position. This device doesn't need the frame or the large amount of iron (just enough to guide the specific fields). There is no rotor, shaft, multiple coils, etc. The device doesn't provide a "step" like a stepping motor (wouldn't it be great if it did).
Now, with reduced weight from the overhead of the stepper (and now even counting gears, shafts, and frame for them), and with much smaller operating ranges, the power-to-weight is greater.
Bruce

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Inverse squared?
Thought it was inverse cubed.
Mike

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force/results/efficiency/etc.
that
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I've said it a few times now. You need iron. I don't care how far you are moving. To paraphrase: Use as much iron as you'll need, not less.
Now, if you are content with very low efficiency numbers (I even doubt 40%) then, by all means, don't use nature's free source of magetic field strength, burn battery power to create it.
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Martin Euredjian
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Martin, I agree, and to re-paraphrase: "Use as much iron as needed, and not any more". ;o)
Do you have a good source for larger neodymium magnets? Not opposed to them, just never found any that I could use. Also, they will need shielding but that is no different than a coil. I'll try anything.
Bruce

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Larger? What do you mean? Large neodymium magnets are downright dangerous. I do mean DANGEROUS, they could smash your finger like it isn't there. Be careful.
Search the www for "neodymium" there are a good number of reputable soruces.

What do you mean by "never found any that I could use"? What are your specifications?

try
Shielding? Explain? Now we are going to have muMetal shields in this thing?
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Martin Euredjian
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Martin, I have literally thousands of neodymium magnets (for magnetic bearings on certain types of equipment). They are dangerous. What I need is one that is 0.6x0.6x0.3 inches big with the poles at center of the faces. Grade N42 or better.
To use magnets of that strength will require managing their field lines...imagine otherwise ;o)
Bruce
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Well, I've got to gracefully exit this thread at this point. Got a very heavy month worth of work ahead of me. It's been real.
-Martin
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dangerous.
Be
soruces.
I'll
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Garrett, Not using piezos. Wasn't me that grabbed the hook. :o)
Bruce

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Actually, what I wrote was something the script writers of Star Trek would be proud of.

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On 28 Aug 2003 11:15:27 -0700, snipped-for-privacy@macetech.com (Garrett Mace) wrote:

Yeah, but I worked with SynthMuscles and I found them to be highly unstable. Their molecular breakdown due to quantum tunneling is a severe problem. I Synthmuscle is an inherently flawed technology.
I wonder if Mr. Bruce has solved the problem yet or if he is merely setting himself up for failure.
EdL
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Ed, I often set myself up for failure, but you are making this way too complicated. The SynthMuscle, as Martin put it, is not a rubbery overly complex trying-to-memic-nature. It is a mechanical device that just needs some simple materials to make it work.
Bruce

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On 31 Aug 2003 05:04:27 -0700, snipped-for-privacy@yahoo.com (Bruce) wrote:

Alright, thanks for giving some information on it. You initiated this with claims of a new technology: synthmuscle. Your claim was that this was a revolutionary new technology that would replace motors and gears. This is a bold claim and bold claims require sufficient documentation to determine their legitimacy, documentation which you had not publicly provided on this newsgroup.
Because of your communication style, my first impression of this thread was that you were some kind of confidence man trying to reign-in suckers. If so, I was intent on stopping your little shinanigans by bringing up questions of the efficacy of the technology you claimed to have.
The challenge I made was necessary to try to establish the veracity of your claims and to steer away any suckers that a con-man might be able to milk for money.
However, since you have allowed me to peruse your yahoo group, I see that you actually have interesting ideas. I see that there is some legitimate claim to having a technology that might possibly replace motors. It is still in a rough state of development, but I think that the technology you have might be capable, with some development, of meeting the claims you make. On that basis, I wish you the best of luck in your endeavor.
Sincerely, Arthur Ed LeBouthillier
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Ed, It does need work. That is why I thought a Team could take it where it needed to go. I know that I can't alone.
To make it available to everyone, that is the reason for making it "open source". For everyone's benifit..for it to go where we all want it to go.
And thanks for the pat on the back (and the iron skillet over the head...definitely need the skillet ;o).
Bruce
snipped-for-privacy@earthlink.net (Ed LeBouthillier) wrote in message (Bruce)

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