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Author Topic: Self accelerating reed switch magnet spinner.  (Read 288867 times)

TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #30 on: October 04, 2013, 10:33:49 AM »
It's up to about 1600 RPM on 24 volts to the drive coil. The switching circuit is drawing 17 mA from the 12 volt supply, including the LED strobe. If I disconnect the LED the switching circuit's draw goes to about 4 mA.

I found that the drive coil works pretty well when it's strapped to one of the frame supports. In this position, the comparator potentiometer varies the duty cycle through the whole range from all on to all off. It looks like about 60 percent HI is optimum. The cap across the coil (instead of a diode) produces an interesting ringing waveform during the off time. A diode, in addition to the cap, has a big effect on this ringdown but doesn't seem to affect the rotor RPM much. A diode across the coil was a great help for the Magnetic Levitator apparatus, though, so I'm not sure which way to go.

Without the capacitor from drain to source, the comparator behaved badly. I thought it was field from the coil causing feedback, and I wasted an hour fooling around trying to get clean pulsing with the drive coil connected. Then I just touched the circuit and noticed that it started behaving better when I touched in certain places. My body's capacitance was helping, especially when I touched both drain and source of the mosfet. So... grab a random small capacitor.... and it worked beautifully!  A 10 nF , 80 V poly film cap.

MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #31 on: October 04, 2013, 03:24:46 PM »
TK:

Off to the races.  I am assuming that with your scope and the judicious placement of one or more tiny decoupling caps you will make the pulse firing rock solid.

If you assume as an example that firing the drive coil between 5 and 10 degrees past TDC imparts the most torque on the rotor, then by adjusting the pot and the pick-up coil angle you can position the energizing pulse to fire between 5 and 10 degrees.  To be more specific, you probably need a kind of "dwell angle" advanced timing for the energizing pulse to get some current flow through the coil ahead of time to give the push at the optimum angle.  It all depends on how short or long the L/R time constant is for the drive coil.  So by observing that on a scope you can get a sense of whether or not you need to move the pick-up coil angle to create the advanced dwell angle.  Of course, you have the scope trigger from the comparator output so seeing the current rise in the coil relative to the firing pulse is easy as pie.

Then with one multimeter showing you the current consumption and a tach showing you the RPM, and the flashing LED showing you the live pulse angle, you can play with the pot and the pick-up coil angle and pickup coil radial distance to position the energizing pulse right at the sweet spot.  You may want to maximize the RPM or you may want to try to get maximum RPM per watt of input.

MileHigh

TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #32 on: October 04, 2013, 03:34:57 PM »
Current version:



TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #33 on: October 04, 2013, 04:50:54 PM »
But...but.... what about all that Bedini action, HV spikes and neons and cap charging and all of that action? This motor is like from Dullsville, man... or is it?

I've now added a NE-2 neon across the 10 nF capacitor from Drain to Source of the mosfet. With S1 closed, bypassing the 1n914 diode, I get extreme spikes of over 250 volts from the drive coil, and these can be utilized in the usual ways, like lighting the neon or charging external caps/batts/whatever. In this mode the rotor actually accelerates even more, and I can trim the potentiometer setting for a bit more ON time in the duty cycle and get substantially more RPM than with S1 open.

Speed right now is 2140 RPM. The scope trace is at 2 ms/div horizontally and 50 V/div vertically, and there are 4 pulses per revolution, so the frequency in Hz shown on the scope x 15 = RPM.


TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #34 on: October 04, 2013, 05:16:38 PM »
Last night when I made the last few posts I was pretty tired. The capacitor is as shown in the schematic, not "across the coil" but rather between Drain and Source of the mosfet, i.e. across the whole power section.

Putting a recirculation diode in the usual position across the coil completely stops all the spike action and makes the Drain signal a clean square wave. But this also decreases the speed of the rotor.

I don't have the inspiration right now to do much more solid mechanical build, to find the real optimum coil positioning and mounting. The comparator set-pot works perfectly to control the duty cycle through the whole range, although the setting is a bit narrow. It might be good to use a smaller value pot here for more spread on the settings.

The thing is running "hot straight and normal" right now, very quiet, brilliant NE2 and about 2150 RPM. I haven't looked at the current draw from the 24v run batteries yet, but as I said before, the switching section uses very little power, especially if I kill the LED.

The LED autostrobe isn't really satisfactory due to the jitter and the fact that it fires on every magnet. It would be better to fire it only once per revolution of the rotor, or have a rotor magnet placement that was precise enough to not jitter. I may try a one-magnet rotor just for grins.... then the strobe would work properly.

TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #35 on: October 04, 2013, 06:03:54 PM »
Sense coil and drive coil (mosfet drain) signals.

The horizontal timebase is at 2 millisec/div. so the frequency shown is about 150 Hz, times 15 = 2250 RPM.
Channel 1 is the mosfet drain, DC coupled at 50 v/div, and the spike is off the screen at over 250 volts. Zero volt baseline is the center graticule marker, also indicated by the mark on the right.
Channel 2 is the sense coil signal, AC coupled at 1 v/div. Since it's offset by 6 volts (the 22k - 22k divider puts it at half the switch Vcc) the true baseline is off the screen bottom. The 6V level is the "baseline" indicated by the mark on the right of the screen.

ETA: The reduction in the ringing waveform is due to the fact that I have a core (a 1/4" steel bolt) inserted in the drive coil. This increases the RPM slightly but damps out the nice ringing oscillation completely if I insert it far enough.

Look at how accurately the comparator detects the "zero crossing" or rather the crossing of the 6V level by the sense signal! It is very precise.

TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #36 on: October 04, 2013, 06:37:10 PM »
It would be nice to have the autostrobe work properly. But flashing on every magnet passage makes it flash 4 times per revolution, so you get a blur instead of a frozen image like you need. One flash per revolution will give the strobe effect properly.
So... digital logic, divide-by-four pulse counter? Or is there an analog way, perhaps using an RC circuit?

I can do it pretty easily using a 4017, I think.

synchro1

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Re: Self accelerating reed switch magnet spinner.
« Reply #37 on: October 04, 2013, 06:37:34 PM »
@TK,


       Unquestionably the highest state of the art in pulse motor circuitry to date. Congratulations on perfecting duty cycle control so elegantly. The speed up coupled with increased back power out defies customary logic. I wonder if a loop back to source would produce a self runner? The 250 volt back spikes are awesome! I bet JLN will bench test a replication.

MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #38 on: October 04, 2013, 07:08:06 PM »
TK:

Quote
It would be nice to have the autostrobe work properly. But flashing on every magnet passage makes it flash 4 times per revolution, so you get a blur instead of a frozen image like you need. One flash per revolution will give the strobe effect properly.
So... digital logic, divide-by-four pulse counter? Or is there an analog way, perhaps using an RC circuit?

"Well, how low can you go?" - asked the Limbo Man.  How about an ultra low tech solution for a high tech problem?

The top of your rotor drum looks like there is silver gaffer's tape on it or perhaps metal foil tape?  Perhaps you can remove it to make a clean surface.  Then I would suggest that you put just one dot lined up over one of the magnets.  Perhaps do it with White-Out correction fluid or a White-Out marker.  Perhaps even just a tiny piece of white paper glued in place.

That's it!  There is nothing else to do!  Just mark the TDC on the top of your red rotor for one of your four magnets and you are done.

A piece of cake!

MileHigh

PS:  Supposing that you put a white dot on the top surface of the drum at the outer edge.  Then if you wanted you could put another dot over the next magnet at TDC but this time it's not at the edge, you move radially inwards by a little bit.  Repeat the process for the remaining two magnets.

Now look at what you have created:  You have four separate and distinct "arcs" or "stripes" that you can see when the LED strobe illuminates the top of the spinning rotor drum.  So that means you can actually see what the timing looks like for the pulse firing for each individual rotor magnet.

synchro1

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Re: Self accelerating reed switch magnet spinner.
« Reply #39 on: October 04, 2013, 08:59:34 PM »

Quote from MH:

"That's it!  There is nothing else to do!  Just mark the TDC on the top of your red rotor for one of your four magnets and you are done."


Not so fast! All that will do is show the dot moving around all four different quadrants, not freezing at one!

TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #40 on: October 04, 2013, 10:25:42 PM »
Synchro is right, because the LED flashes with each magnet passage, with a single dot on the rotor, you will see four blurry images with the dot in each of the four positions, and arcs will be even worse. The flash has to happen once per rotation of the rotor, and there's another complication: the pulse is too broad to freeze motion. The rotor moves many degrees during a single flash of the LED! The pulse width required to properly freeze the motion of the rotor is surprisingly narrow. This narrowness makes the light from a standard LED pretty dim. Usable, but dim.

The 4017 solution to divide by 4 (or whatever other number from 0 to 9) is very easy to implement. Shortening the output pulse to the LED is harder... it has to be really short.

Please watch my next videos. I'm processing and they should be ready in a half hour or so.


synchro1

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Re: Self accelerating reed switch magnet spinner.
« Reply #41 on: October 04, 2013, 10:43:32 PM »
@TK,


       You could cut a narrow slit through a piece of paper and tape it to the LED.

MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #42 on: October 04, 2013, 11:07:32 PM »
I guess it depends what you want the strobe to do.  I wanted the "strobe" to be ON when the drive coil is being energized.  So it's not a "flashing strobe" it's a constant illumination for a short period time during the conduction angle.  I will call it a "pulse of light" to avoid confusion.

If you have only one dot on the top of the rotor then and there are four pulses of light per rotation, then what do you get?   Supposing that you are illuminating the area near the drive coil, and you are _looking_ at the area near the drive coil.   The first pulse of light illuminates the dot and you see a streak of white corresponding to the full conduction angle showing when the coil is energized.  The other three flashes just illuminate the red surface of the rotor.  So for every four pulses of light you get, "white-streak, red, red, red" and then it repeats.  This should still be easily visible to your eyes.  The white streak might look "translucent" but it will still be there.

There is no intention to freeze motion with the light pulse - you want to observe the changing conduction angle as you tweak the setup.

TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #43 on: October 04, 2013, 11:08:41 PM »

TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #44 on: October 04, 2013, 11:21:43 PM »
I guess it depends what you want the strobe to do.  I wanted the "strobe" to be ON when the drive coil is being energized.  So it's not a "flashing strobe" it's a constant illumination for a short period time during the conduction angle.  I will call it a "pulse of light" to avoid confusion.

If you have only one dot on the top of the rotor then and there are four pulses of light per rotation, then what do you get?   Supposing that you are illuminating the area near the drive coil, and you are _looking_ at the are near the drive coil.   The first pulse of light illuminates the dot and you see a streak of white corresponding to the full conduction angle showing when the coil is energized.  The other three flashes just illuminate the red surface of the rotor.  So for every four pulses of light you get, "white-streak, red, red, red" and then it repeats.  This should still be easily visible to your eyes.  The white streak might look "translucent" but it will still be there.

There is no intention to freeze motion with the light pulse - you want to observe the changing conduction angle as you tweak the setup.
Just please watch the video. All you see under your conditions is a blur. Don't forget that I have the hardware set up, this is NOT a thought experiment for me! You will never be able to see the angular display you are looking for under ordinary illumination. The way to get what you want is to have a double flash strobe hitting the beginning and trailing edges of the longish dwell.
I also have a bit of experience with strobes, flash photography, engine and motor timing issues, digital and analog electronics. As well as operating test equipment in order to make it do what I need to do. Just watch the video, it will be ready soon.