Author Topic: Self accelerating reed switch magnet spinner. (Read 291755 times)

synchro1 · « **Reply #180 on:** October 15, 2013, 11:56:41 PM »

@TK,

Sheer genius! That could mount on the top of a Coanda lift body and fly around like a new spy drone.

TinselKoala · « **Reply #181 on:** October 17, 2013, 04:43:16 AM »

Actually I think we have just about invented the brushless DC "outrunner" motor and its op-amp pwm controller.

MileHigh · « **Reply #182 on:** October 17, 2013, 07:41:09 AM »

It looks like a 3-wire interface to the coil array. Two power signal wires and a fat common ground return wire. A few basic tests with a D-cell and a compass/small magnet and you could figure out what energizes what and with what polarity. It would be a fun project to make a motor controller for that. An Arduino software project or go analog. The design of the timing circuit opens up a lot of possibilities.

I think of the power booster circuit for the driver. If you make a voltage servo amplifier like the power booster in theory there is no need for any recirculating diodes or back-EMF collection system. The power booster circuit would literally suck up any kick-back from the coils.

In my mind it would be fun to go in "blind" without knowing what the real controller does. You can see how the motor could be made to act like a sort-of stepper motor at low speeds. But with sophisticated electronics, could you make it turn smoothly at low speed? What about torque? Only the mad scientist knows.

P.S.: I just noticed that the circuit is AC-coupled. There must also be a DC-coupled version of a power booster.

synchro1 · « **Reply #183 on:** October 17, 2013, 05:49:12 PM »

@TK,

Bust your old VCR open and you should find an "Outrunner" motor just like that one already attached to the bottom of the bearing! I tried to wire mine "Imhotep" style, but failed to get it to work. I think you and Milehigh may be re-inventing the wheel!

TinselKoala · « **Reply #184 on:** October 17, 2013, 07:15:38 PM »

I haven't yet looked at the motor in a VCR head.

The brushless outrunner and other brushless DC motors that use three wires: all three wires are "equal". They can be hooked to the controller's 3 wire output arbitrarily. If the motor turns in the wrong direction, any two of the wires can be reversed and then the motor will turn in the other direction.

Here's some info from a very complete app note that describes just about everything you need to know about these brushless DC motors and their drive circuits.

Quote

Sensorless Motor Control
It is possible to determine when to commutate the
motor drive voltages by sensing the back EMF voltage
on an undriven motor terminal during one of the drive
phases. The obvious cost advantage of sensorless
control is the elimination of the Hall position sensors.
There are several disadvantages to sensorless control:
• The motor must be moving at a minimum rate to
generate sufficient back EMF to be sensed
• Abrupt changes to the motor load can cause the
BEMF drive loop to go out of lock
• The BEMF voltage can be measured only when
the motor speed is within a limited range of the
ideal commutation rate for the applied voltage
• Commutation at rates faster than the ideal rate
will result in a discontinuous motor response
If low cost is a primary concern and low speed motor
operation is not a requirement and the motor load is not
expected to change rapidly then sensorless control
may be the better choice for your application.

So for the sensorless system, the motor is driven by energizing the phases cyclicly, and using the non-energised phase's BEMF as the "sensor" to tell the controller what's up.

This is a long but very interesting document (48 pages). I recommend it for anyone working with brushless motors. There are schematics and program code for both sensored and sensorless drivers.

TinselKoala · « **Reply #185 on:** October 17, 2013, 07:22:29 PM »

@MH: It looks like the "power booster" circuit just allows the op-amp to switch the output transistors, which allow more current to flow through the load. Since our present design uses the op-amp to switch a power mosfet I don't think the power booster applies. But the idea of using a half-bridge, grounding the motor load thru the bottom transistor, instead of letting it "float" when off, might be useful.

picowatt · « **Reply #186 on:** October 17, 2013, 07:44:49 PM »

Regarding high side current sensing:

http://www.analog.com/library/analogdialogue/archives/42-01/high_side_current_sensing.pdf

Something like this,

http://www.analog.com/static/imported-files/circuit_notes/CN0116.pdf

driving an active integrator with low drift and high DC precision (instead of just a passive RC).

PW

e2matrix · « **Reply #187 on:** October 18, 2013, 01:31:59 AM »

Quote from: TinselKoala on October 13, 2013, 04:19:00 PM

Yes, that's a great classic text all right, thanks for finding it. I found the Sams classic "Op Amp Cookbook" by Walter Jung in the used bookstore a few weeks ago and of course I scraped together my lunch money to buy it.

All op amps are not created equal. Many really do need the bipolar power supply to do their best work (like your analog power computer). Many can be used in single-supply mode as we have been doing. Some are more better for audio work, some are best for comparator applications, some are general purpose, some require dealing with more input and output options rather than just the two ins and one out of the opamps in the TL082 chip. Apparently I once again "aced" accidentally by choosing the TL082 for this application because of the very high impedance JFET input stage and the fast slew rate, and the fact that it works well on the single supply mode. And ease of use, low cost, and easy availability.

Here's something I found just a couple days ago, which made me very excited. This is another "classic" from a bygone era. The chips it talks about are still available, and many of them exist now in advanced versions that use very low power and are very sensitive. There are many many useful circuits and concepts covered in the TTL Cookbook.

ftp://apollo.ssl.berkeley.edu/pub/cinema/04.%20Science/TTL%20Cookbook_0672210355.pdf

It's a 12 MB pdf, an excellent scan, all 340 pages, clear diagrams and even the photos aren't too completely black.

ETA: I just checked EBay for sellers of TL082CN .... if you are willing to wait two weeks for a shipment from Thailand, you can get 10 for $2.79, free shipping. Or.... 50 for $9.99 from the same seller in Bangkok.
Twenty cents apiece! Delivered to your door! How can this even be possible at all?

This guy http://www.thaishine.com/servlet/the-939/10-x-TL082-TL082CN/Detail has them 10 for $4.83 which includes shipping. I've bought a lot of things from him and he is very fast to ship and very nice to deal with. He sells a lot on eBay also but not sure if he has that item up on eBay. His own web site prices are a little less than his eBay prices too.

TinselKoala · « **Reply #188 on:** October 18, 2013, 07:04:17 AM »

Ah, yes, I got my BC337s from him, along with a couple of other items, from his EBay store. I think I'll place another order.... you are right, the prices on his website are cheaper, I could have gotten 100 transistors for about the same as I paid for 50 on the EBay store.
Shipping from Colorado, no charge, is a real plus for those of us in the USA.

TinselKoala · « **Reply #189 on:** October 18, 2013, 07:53:59 AM »

Quote from: picowatt on October 17, 2013, 07:44:49 PM

Regarding high side current sensing:

http://www.analog.com/library/analogdialogue/archives/42-01/high_side_current_sensing.pdf

Something like this,

http://www.analog.com/static/imported-files/circuit_notes/CN0116.pdf

driving an active integrator with low drift and high DC precision (instead of just a passive RC).

PW

Nice advice, added to the MH analog computer idea.

Where you been? We had a bit of fun there a little while ago with LMM, and missed your participation. I hope you watched my "highlights" of the demonstrations.

picowatt · « **Reply #190 on:** October 18, 2013, 03:27:34 PM »

Quote from: TinselKoala on October 18, 2013, 07:53:59 AM

Nice advice, added to the MH analog computer idea.

Where you been? We had a bit of fun there a little while ago with LMM, and missed your participation. I hope you watched my "highlights" of the demonstrations.

LMM?

TinselKoala · « **Reply #191 on:** October 18, 2013, 07:52:57 PM »

Quote from: picowatt on October 18, 2013, 03:27:34 PM

LMM?

Little Miss Mosfet.

TinselKoala · « **Reply #192 on:** October 18, 2013, 07:59:09 PM »

Meanwhile, here's an illustration of siphoning off the spike to power an external circuit. It quickly charges the reservoir cap of the little 2-element ring oscillator and provides power to run it quite well. At the end of the video as I discharge the cap I was lucky enough to capture a single frame showing the shower of molten metal and plasma from the tiny spark.

Video is uploading and will be ready in a few minutes at
http://youtu.be/T5I_BM4E00E

The frame capture of the spark discharging the main 150 uF cap is here:

TinselKoala · « **Reply #193 on:** October 18, 2013, 08:14:13 PM »

And some power measurement considerations. I am powering the driver/strobe unit from the lower 12V battery of the 24 volt stack, and I can turn off the strobes, but obviously I can't turn off the driver or the motor will stop running. But I'd like to be able to separately measure out the power to the driver/strobe circuit and the power to the drive coil. So far, I know this: I can get the motor to run stably at 750 RPM, moving air with the prop, and drawing about 48 mA with the strobes on, and around 31 mA with them off. And I know that, with no drive coil connected, the driver circuit, without the strobes, also draws around 18-20 mA.

So, it would seem that I am running the drive coil itself on very little power indeed, once the driver and strobe powers are accounted for.

However... since the measurement points are as shown in the diagram below, I'm not sure about the validity of the measurements since the supply voltages are split the way they are, but all the current goes thru the milliammeter.

Any help or comments appreciated.

synchro1 · « **Reply #194 on:** October 18, 2013, 10:39:35 PM »

@Tinselkoala,

Does the rotor speed up when the BEMF power's collected by the capacitor?

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Author Topic: Self accelerating reed switch magnet spinner. (Read 291755 times)

synchro1

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