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Author Topic: Self accelerating reed switch magnet spinner.  (Read 269592 times)

Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #60 on: October 06, 2013, 03:14:41 AM »
A slight revision to the basic circuit diagram:


Offline synchro1

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Re: Self accelerating reed switch magnet spinner.
« Reply #61 on: October 06, 2013, 04:49:47 AM »
@TK,


        I believe a 3D printer can manufacture the rotor part I described, and the design file can go into public domain freeware like Lasersaber's miser motor, accessable to all. Everything else is store bought. The rotor sleeve can be printed too with a square inside. This gives us two firewalls including the PVC housing to protect us from high speed disintegration. I believe a superior rotor and shatterproof housing like this would couple well with your brilliant MHOP circuit design, much more elegant than anything Farmhand ever created.

Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #62 on: October 06, 2013, 06:08:39 AM »
Not my design, exactly. Mile High laid out the idea, the working principle and all the specifications, I just built it. And he gave me some critical advice along the way, too.

I solved a couple of problems and learned a lot building it, and it's not done yet. The op-amp board needs to have a regulated 12 volt supply that runs from the same batteries that drive the coil, and that's tomorrow's task. Some mechanical cleanup and the implementation of the adjustable positioning of one of the coils, for exact timing, will also be done tomorrow, I think.

I also think the sense coil can be a lot smaller, but I don't have any small magnet wire, just lots of #27.

I'm not sure I'd trust something made on a consumer-grade 3d printer rotating at high speeds. But I have no experience with those things, they have suddenly appeared while I was on Mars or something and I don't think I've ever actually worked with a printed part.

Offline MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #63 on: October 06, 2013, 07:04:47 AM »
TK:

Thanks for giving credit where credit is due.  The MileHigh pulse motor circuit has a certain ring to it.  It's "radically different" from just about anything we have seen before.  To tell the truth I have mentioned it many times in the past but nobody would acknowledge it.  So I am glad and thank you for building it.  Perhaps it will get the creative juices flowing with some of the pulse motor builders.  That includes trying different sense coils.

The challenge for the pulse motor builders is to relate the geometry of the rotor magnet and it's associated magnetic field with the geometry of the sense coil and the resultant EMF output.  It's about understanding the interactions.  You have to be able to look at the scope trace of the sense coil output and try to understand why it is the way it appears on the scope and relate that to your setup.  Then perhaps try another geometry for the sense coil and look at the scope trace and try to understand that.  In other words, understand the basic interactions between a magnet and a coil.  That way you can start to design your motor with the physical configuration of the rotor and the drive coil and the sense coil in mind.  To do a mini rant of sorts, how many times have you heard people say, "How many turns and what gauge of wire for your coil?"  Do they actually use that information in a meaningful way beyond just by-the-numbers replication?  Chances are in the majority of cases, the answer is no.

Probably the next step for pulse motor builders is to look at the current waveform in the drive coil when it is energized and understand how the inductance and resistance of the coil wire and equivalent series resistance of the drive circuit affects the rising current waveform.  Also look at what influence the passing rotor magnets have on the rising current waveform.  So perhaps a standard investigation for builders would be to look at the current waveform without any rotor interaction and then look at the current waveform with the rotor spinning and understand the differences between the two (assuming there are differences).

Some people in this hobby advance and improve their skill set and knowledge year after year and some people just tread water year after year.  Perhaps the MileHigh pulse motor circuit will encourage some people to push themselves to learn and experiment more.

Here is a thought:  If you have a rotor with four magnets spaced 90 degrees apart, what is your maximum desirable conduction angle starting from top-dead-center with the assumption that our design goal is for maximum RPM?  The answer is 45 degrees.  I am not asking you TK, but rather I am asking the greater pulse motor builder readership:  Why is it 45 degrees?  This is just an example of the little details that all can go into making a better pulse motor.

Note that with the MileHigh pulse motor circuit you should be able to set the conduction angle to exactly 45 degrees with a minimum of fuss with near-perfect switching.  In contrast, with a conventional Bedini transistor-based design this would be impossible to do.

MileHigh

Offline MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #64 on: October 06, 2013, 07:39:50 AM »
I also think it's worth mentioning again that there is no current flow in the sense coil.  The sense coil is a "pure EMF" device.  So that means that you can try a sense coil with thousands of turns based on super fine wire if you want to.  You can do anything you want.

However, like a proverbial chipmunk cracking an acorn eventually you will build up the knowledge to make your own design choices.  You might need an 800-turn sense coil or you might not.  Making those kinds of design decisions are supposed to be part of the fun.

MileHigh

Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #65 on: October 06, 2013, 08:05:55 AM »
Yep.

I particularly like the fact that a starting spin is not needed, and that it will run in either direction and still make all the spike and HV action you could desire. Also the strobe LED is really a neat feature. It allows tuning to the sweet spot instantly.



Offline synchro1

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Re: Self accelerating reed switch magnet spinner.
« Reply #66 on: October 06, 2013, 08:11:00 AM »
@TK,


       The computer generated design file can be emailed to professional 3D printer outfits, there are a handful, who print on the most sophisticated printers. The choice of materials includes a variety of metals. They make castings from the 3D molds. Try and catch up with the process simply by typing 3D printer in the google search engine, and spending a half hour in study. I'll go ahead with my project independently, then after testing and uploading a video, you'll be free to download and email the design file to the printer site of your choice. Naturally, you are required to pay them, then they express mail you the finished part. NASA is building internal rocket engine parts this way. You guys are invited to suggest magnet strengths if you want to, or anything else. Let me point out that the current design would allow us the versatility of selecting between two or four monopoles or a bipolar and staggered polarity of four.


       A compact and nearly frictionless high speed rotor of this size would only require a thread spool size power coil to reach top speed, and I believe also a sensor coil of the same dimension and Ohmic resistance would be best. My power coil was a series bifilar, not to resurrect the old vendeta, because it goes faster.

Offline conradelektro

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Re: Self accelerating reed switch magnet spinner.
« Reply #67 on: October 06, 2013, 11:15:10 AM »
................
I also think the sense coil can be a lot smaller, but I don't have any small magnet wire, just lots of #27.
.................
@TK:
 
You could use the coil from a relay as a sense coil

http://www.overunity.com/13523/has-anyone-seen-lasersabers-new-motor-runs-on-1000uf-cap/msg363167/#msg363167,
http://www.overunity.com/13523/has-anyone-seen-lasersabers-new-motor-runs-on-1000uf-cap/msg363297/#msg363297

with or without the core. I  guess any relay would do. 24V or 48V relays have more wire and higher DC resistance.

It is a bit tricky to get the coil out of some relays. I do it with a hack saw, a drill and a file. The relay has to be held in a vice. The soldering posts should be left in place in order to avoid handling of the very thin wire.
 
The drilling is best done with a box column drill press while the relay is held in a machine vice. In most relays the coil core has to be drilled free on one side (usually from the base of the relay). But this could be done with a file.

Did you try "repulsion mode" with your set up?

Very nice sensing circuit and the TL082 is a very interesting and versatile OpAmp.

Greetings, Conrad

Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #68 on: October 06, 2013, 12:06:16 PM »
@synchro: thanks, that's very generous of you.

@conrad: Yes, I've considered using a relay coil for the sense coil. I have a handful of little relays from TV sets that aren't much good to me because they are normally open SPST. I want to stay coreless for both coils though and I'm not sure about getting the core out of one of those coils. I may have to just unwind the wire and wind onto a different former with no metal core. Getting the coil out of the relay is not problem, it's getting the core out of the coil. It would be too nice to find that they used a slipon bobbin that just slips off the corepiece.

I haven't yet tried repulsion mode. I want to arrange for one or the other of the coils to be movable for timing first. Right now the thing is "by chance" timed well and will run very well in either direction. It is easier to start using the setpoint pot alone in the "wrong" direction but it reaches slightly greater final RPM in the "right" direction. I have the starting technique now, it's very easy to start just by turning the setpoint pot properly.

Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #69 on: October 06, 2013, 01:44:19 PM »
New sense coil, made from a relay core. It took about half an hour with file, hacksaw and nippers to get it out and remove the core.

It produces a higher voltage peak (surprise surprise) and I'm still experimenting with mounting location.



Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #70 on: October 06, 2013, 07:25:33 PM »
The switching electronics may not need to be tightly regulated, just heavily filtered. I just tested it and there's no change in the motor behaviour at speed, with a supply of 8 1/2 to 15 volts DC to the opamp/LED strobe circuitry.


And I have to report a major error in my reporting.

The rotor isn't made from a peanut butter jar lid at all.

It is actually a Folger's Instant Coffee jar lid.

I apologize if this has caused any confusion. Replicators will have to see if they can trade their leftover PB for some instant coffee.

 :o

Offline MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #71 on: October 06, 2013, 07:46:31 PM »
TK:

Keep on trucking!   Again standard disclaimer, I am just going to make some comments but I am not asking you to do anything.  You just play around at your own pace and do your thing.  The comments are meant to be generic for everyone to consider.

I can see from the scope shot that you are working in attraction mode.  From your last clip we saw the drive coil and the sensor coil are roughly opposite each other.  Notice in your scope shot above that when the MOSFET shuts OFF that the change in flux from the drive coil is picked up by the sensor coil.  Obviously the motor is functioning fine and the switching looks very clean.  In a typical Bedini motor with a coaxial drive and sensor coil, we assume that switching the drive coil ON tends to induce EMF in the sensor coil to switch the drive coil OFF.  Conversely, we assume that switching the drive coil OFF will tend to induce EMF in the sensor coil to switch the drive coil ON.  Now in your case, we have the sensor coil rotated by roughly 180 degrees and on the opposite side of the rotor.  Therefore, one can assume that switching the drive coil OFF would tend to induce EMF in the sensor coil to switch the drive coil OFF.  That would tend to reenforce the process and create a "snap" action.   Note however, that it's not that simple because we see a "doublet" impulse spike induced on the sensor coil EMF.  We assume that the op-amp input is very sensitive and this will cause a tiny glitch on the op-amp output.  From what I can see it looks like there is the initial switch OFF, followed right away by a very short switch ON for a few microseconds.  That is shown in the "extra thickness" of the rising edge of the drive coil waveform, and the "doublet" impulse we see on the sensor coil waveform.

Again, I realize that you are doing your thing and there is nothing "wrong" in the last clip and the waveforms captures you posted.  You can see how there is an advantage to having the sensor coil at 90 degrees to the drive coil to greatly reduce the mutual induction between the drive coil and the sensor coil.   Also, a very very tiny cap between the sensor coil input on the TL082 and the pin 4 ground on the TL082 should help.  You would have to scope this and find the "Goldilocks" value that just filters the EMF signal from the sensor coil a tiny little bit.  Similarly, a 0.1 uF capacitor between the -ve input on the TL082 (pin 2), and the pin 4 ground should help.  This is the output from your 10-turn potentiometer.  So adding a small decoupling cap here works to ensure that your reference threshold voltage is inherently stable.  I see that you added the 220 uF and the 0.1 uF for the power for the TL082 which is great.

What you are trying to do is create a stable voltage environment for the TL082 for it's power, as well as for the two differential inputs.  The critical thing is to not over decouple the EMF coming from the sensor coil.  You just want to give it the lightest of decoupling so that you reduce or eliminate any high frequency noise on the signal.  Too much decoupling capacitance and you risk creating an LC tank circuit which you want to avoid like the plague.

Anyway, thanks again for making clips and doing screen shots.  I am amazed that you have more than 500 clips up on your YouTube channel now.  Note that you also have a "lid motor" going.  How about them apples!

MileHigh

Offline MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #72 on: October 06, 2013, 08:22:02 PM »
Just a few comments about switching and coupling as more food for thought.

For starters, since we are playing with coils and differential inputs on an op-amp, there are many ways to invert the signals.  Let's assume that we are not going to include the rotor magnets as an option, they will remain fixed.

What are the options for "inverting the logic" of the motor?

I can think of:

- swap the wires on the drive coil
- swap the wires on the sensor coil
- swap the -ve and +ve inputs on the op-amp
- you could even invert the logic on the drive coil itself and tie one end to ground instead of +12 volts and change the driver circuitry

What is the point of all of this?  Let's assume that you simply can't eliminate the mutual coupling between the drive coil and the sensor coil.  However, you should be able to use that coupling to your advantage.  Note that you have to keep in mind that the op-amp inputs are very sensitive, and the amplification gain on the output from the differential inputs is typically in the millions or greater.  Any kind of differential noise on the differential inputs in an op-amp comparator configuration will make the op-amp output toggle between ground and +12 volts at the same speed as the noise.

To use the mutual coupling to your advantage you want this to happen:  When the you switch the drive coil ON, then the EMF induced in the sensor coil from the mutual coupling wants to switch the drive coil ON.  Similarly, when you switch the drive coil OFF, the EMF induced in the sensor coil from the mutual coupling tends to switch the drive coil OFF.

So as you can see, you don't necessarily have to obsess on reducing or eliminating the EMF induced in the sensor coil from the switching of the drive coil.  You don't necessarily have to obsess on getting the sensor coil at 90 degrees and the precise offset angle to reduce or eliminate the mutual coupling.

Instead, you could easily live with a small amount of mutual coupling and try to use it to your advantage.  It's arguable that if the small amount of mutual coupling reenforces the switching, then you will get the "snap" effect in both directions.  With the right configuration and the judicious application of capacitive filtering on the -ve and +ve inputs on the op-amp, you could get rock-solid clean and robust switching.  The fun part is that you have to put your thinking cap on and figure out what the logic of the coupling is doing.  You might have to invert the logic somewhere, or you might not.

Note that the op-amp switching is already very clean, so you are not looking for extra slew rate with the "snap," you don't need it.  Rather, the "snap" is there to improve the robustness and overall noise immunity of the circuit to external influences.

MileHigh

Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #73 on: October 06, 2013, 09:13:04 PM »
Yes, it was always the intention to have the sense coil at about 90 degrees from the drive coil, I just didn't have the mount made for that yet. But I do now. Now I have full control over timing (by moving the sense coil around in angular position) and dwell (the setpoint control) and I can start the rotor in either direction simply by manipulating the setpoint control, no manual starting spin necessary.

Yes, I'll scatter some decoupling caps around the circuit, and there is a bit of glitchiness, perhaps due to coupling between the coils, but overall the thing is working great, and even has a fair amount of torque once it's spinning at speed. The duty cycle for best speed is about 65-70 percent ON.

I have the switching electronics running off the low side 12 volt battery of the 24 volt stack now, no regulator or external separate PS needed.

In the photo, which is a top view, the Drive coil axis is just about the same as the twisted green wires on the left. The drive coil itself is black and hard to see but it's the same one in the same place as before. The Sense coil is mounted on a bit of threaded plastic rod, which is mounted to the black popsickle stick which is pivoted on the top pivot bearing mount, so it stays concentric with the rotor as I vary the angular position (timing).

ETA: How can you tell it's operating in attraction mode? I haven't tried it in repulsion mode yet, so I don't know for certain, but it seems to me, in my morning fog, that the waveforms and the phase relationship between the sense and drain signals will still be the same.

Offline MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #74 on: October 06, 2013, 10:10:58 PM »
TK:

The angular adjustment for the sensor coil looks great!

How can I tell it's operating in attraction mode from the scope shot?  In looking at the sensor coil waveform I can see the "zero cross" is the center of the steep negative slope between the positive and negative humps.  That's also top-dead-center for the rotor magnet fly-by.

In looking at the drive coil waveform I can see that the switching is ON BEFORE the "zero cross" and it switches OFF at the "zero cross."  Hence the motor is running in attraction mode.

If I saw the drive coil being switched ON at the moment of the "zero cross" and it then switched OFF a certain amount of time AFTER the "zero cross" then I would know the motor was running in repulsion mode.

You can also see the switching angle of course.  To be more precise, you can clearly see that your actual switching threshold is actually set below the "zero cross" of approximately six volts.  Your switching threshold is set to let's say rougly five volts.  i.e.; negative one volt relative to the "zero cross."  Again, this is impossible to do with a conventional Bedini motor.

MileHigh