1000000 RPM magnet video - would like the schematic!  - Page 1
Forum section: electronics / projects

author: applicanon
author_rank: Contributor
timestamp: December 05, 2019, 02:36:41 pm
content: I saw a video a few years ago which was quite impressive, and I would like to duplicate the results. The video was of a fairly simple circuit which utilized a hall effect sensor, a coil, a mosfet, and various neodymium magnets. When the circuit was operating, it pulsed the coil at high frequency, causing the magnet to rotate at extremely high RPM. The coil pulses were triggered by the hall effect sensor which was in turn triggered by the rotating magnet.The video shows a super simplified version of the circuit, but I would like to have a schematic complete with part numbers etc. which would allow me to simply build it myself without any trial and failure. If anyone out there can help me with this I would very much appreciate it, as would many others, as I'm sure it will be a popular project for people to put together.Last but not least, the link to the video!

author: applicanon
author_rank: Contributor
timestamp: December 05, 2019, 02:48:38 pm
content: OK so it turns out the schematic is available on the guys website!I don't really understand some of the things on the drawing, however.. Can anyone fill me in on what the item is which is labelled "BP" / "BP2"?? I'm guessing it may be a push button?? If it is a button, why 4 terminals? Is it normally open or normally closed? Is it not a button at all??I'm assuming the coil gets connected between terminals "BB1" and "BB2".The hall effect sensor connection points are easy enough to interpret.Hope someone else thinks this would be a fun project too and will join me on this build!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 05, 2019, 05:12:49 pm
content: "BP", looks like "Bush Putton".Or "Button, Push" may be more grammatically correct in their original language (French?).Seems the purpose is to pulse the circuit just to give an initial kick.Q2 and Q3 appear to be swapped and reversed. I think they are intended to be a complementary emitter follower, to drive the gate; as shown they would just short out the supply, not very fun. R4 isn't really needed and can be removed (shorted out).Note that the loop between Q4, D3 and C3 must be short; place them close together.Beware that the output transistor is unlimited in current, and is dumping all the reactive (magnetic) energy from the inductor into a diode, which is shorting out the inductor half the time, which won't do any favors for discharging said magnetic field. It may be better to place a TVS in series with D3, though it will probably get rather hot rather fast. Better still, dump the energy into a capacitor (making a boost circuit), then dissipate the energy more gradually with a power resistor (discharging the capacitor's excess charge into the supply).The next best thing is switching both the top and bottom of the coil at the same time (called a two-switch flyback converter), but this requires more hardware to pull off, so I won't try to list all the changes that would need..The concern is that, if you expect real mechanical power out of this system (i.e., a few watts of friction is probably spent bouncing around that magnet), expect poor efficiency, say 10s of watts input. A lot of which will be lost in the magnetic field, which is weakly coupled to the magnet on account of the air-core coil, the large distance between them and so on. So the circuit will be a boost converter, first and foremost, with a quirky side-effect of also making a magnet spin.Tim

author: capt bullshot
author_rank: Super Contributor
timestamp: December 05, 2019, 05:49:27 pm
content: Quote from: T3sl4co1l on December 05, 2019, 05:12:49 pmThough agreeing to the rest, I disagree here. To me it looks like it's intended the way it's drawn and is drawn correctly. Q2 and Q3 would be an inverting driver stage, R3 turns on Q3 when Q1 is off, R4 turns on Q2 when Q1 is on. Kind of unusual (not as one would expect) and maybe ugly, but should work.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 05, 2019, 06:11:41 pm
content: Nice!That looks like the ideal setup to test if a magnet turned very fast would produce electromagnetic waves or not. Turn the magnet, cut the power, then with a receiver look for any corresponding radio waves coming from the swirling magnet.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 05, 2019, 06:12:23 pm
content: As shown, Q3 keeps Q1's collector between ~0.1V (Q1 on) and 0.7V. In either case, R4 has 4V across it, so Q2 is hard on and current will be limited by hFE, to a few 100 mA.Tim

author: capt bullshot
author_rank: Super Contributor
timestamp: December 05, 2019, 07:32:17 pm
content: Dang, you're right. One could use BS170 / BS250 instead to make it work as shown or use the emitter follower configuration.

author: Yansi
author_rank: Super Contributor
timestamp: December 05, 2019, 07:42:36 pm
content: Quote from: capt bullshot on December 05, 2019, 07:32:17 pmWould not work.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 05, 2019, 09:23:47 pm
content: Right, changing Q3 to Nch would do, though it would still be slow.Both, complementary, say 2N7002/BSS84, it's not bad, but rather slow to drive from a pullup resistor. I'd rather have the emitter follower in front.The cross-conduction wouldn't be too awful at 5V supply, at least (under 300mA, for a few 100 ns at a time).Tim

author: Yansi
author_rank: Super Contributor
timestamp: December 05, 2019, 09:28:04 pm
content: Note just replacing the PNP with a P mos and NPN wit Nmos will put it into heavy cross-conduction.

author: iMo
author_rank: Super Contributor
timestamp: December 05, 2019, 10:04:28 pm
content: Does it turn 1mil rpm? I doubt so..

author: applicanon
author_rank: Contributor
timestamp: December 06, 2019, 07:43:24 am
content: Why doubt? If the transistor can switch at 1 megahertz or greater, and the magnet can keep up with it, then thats your 1 mil rpm... guy shows the hall effect sensor on the scope pulsing at 1 mhz in the video doesnt he? that represents the magnet rpm right?

author: RoGeorge
author_rank: Super Contributor
timestamp: December 06, 2019, 08:01:30 am
content: RPM stands for Rotation Per Minute, not per second. 1 MHz at sensor switch means 60 million RPM.Also, 1 mhz means nothing, 1 mHz = 0.001 Hz, while 1 MHz = 1 000 000 Hz.

author: iMo
author_rank: Super Contributor
timestamp: December 06, 2019, 08:41:32 am
content: The hall sensor could show 1MHz, sure, it does not necessarily mean a) the sensors senses the magnet, b) the magnet rotates 1mil times per second, however..

author: Yansi
author_rank: Super Contributor
timestamp: December 06, 2019, 08:52:24 am
content: The hall senzor will certainly not work @1Mhz, neither will the rest of the stupid driver circuitry.As was already kindly pointed out, 1M RPM = 16.67 RPs (16.67 kHz). Which is well within the capability of a generic hall sensor and the driver circuit.Also note, that there may be multiple flux changes per physical revolution of the magnet, as the circuit may feedback on itself or any kind of harmonics.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 06, 2019, 09:22:07 am
content: Should be possible to measure the RPM optically, with a LED stroboscope and a painted magnet, as a double check.

author: applicanon
author_rank: Contributor
timestamp: December 06, 2019, 09:49:10 am
content: ima build a better version tomorrow based on this...Vin is the hall effect sensor output.

author: iMo
author_rank: Super Contributor
timestamp: December 06, 2019, 10:24:03 am
content: If I were you I would start with a simulation..

author: Yansi
author_rank: Super Contributor
timestamp: December 06, 2019, 10:31:13 am
content: To hell with that C1... and lower the value of R1.Another interesting idea with some clear benefits;)

author: applicanon
author_rank: Contributor
timestamp: December 09, 2019, 10:09:44 pm
content: YANSIDo you mind explaining the circuit you posted? What are the clear benefits that you are suggesting? Please give some additional info! Thanks

author: Yansi
author_rank: Super Contributor
timestamp: December 09, 2019, 10:44:17 pm
content: Least amount of components to implement an (unfortunately) inverting voltage amplifying gate driver, that does not go into cross conduction during a transition.

author: james_s
author_rank: Super Contributor
timestamp: December 10, 2019, 03:52:40 am
content: If you're gonna try to spin anything up to a million RPM you'll want to set up a very sturdy blast shield. Even a tiny magnet spinning that fast will be dangerous, the forces created by the rotation will be tremendous and if it breaks up you will have a shower of potentially supersonic tiny little bullets.

author: applicanon
author_rank: Contributor
timestamp: December 10, 2019, 03:57:05 am
content: James,if you watch the video, there is a magnet explosion which occurs and is shown! Yes, the centrifugal force upon the magnet literally ripped the magnet to shreds!Very dangerous indeed.

author: Jwillis
author_rank: Super Contributor
timestamp: December 10, 2019, 04:04:05 am
content: I had a toy a few years ago that consisted of a magnetic top that opposed a magnetic base. If you got the base perfectly level the top would spin and levitate . I wonder its you could do the same thing here by making your winding perfectly level. It sure looks like the ball wanted to levitate at the centre of the coil. Of course your coil would have to be perfectly round . Or as near as prefect as you could get.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 10, 2019, 11:12:08 am
content: That toy is called Levitron.Levitron arrangement is a very clever way to circumvent the Earnshaw's theorem, which roughly says a magnet can not be made to levitate using only magnets (no matter how many permanent magnets are used, there is no arrangement that can levitate another magnet on top).https://en.wikipedia.org/wiki/Earnshaw%27s_theorem

author: Yansi
author_rank: Super Contributor
timestamp: December 10, 2019, 11:18:12 am
content: But it does not levitate by itself. It uses rotating mass to stay put on.Otherwise, there is an active circuitry inside to balance it.