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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Steve Conner wrote ...
Jmartis wrote ...
it is not stable (the levitated object sticks to the electromagnet above it)
Did you see the earlier posts that mention the need for a lead compensation circuit to keep it stable?
yep I saw those posts, but didnt have opamp(s) handy so I tried it without them, of course it didn't work. I will buy the LM324 and make the lead compensation (similar to cjk2's) but I have just one IR photodetector so I am not sure if it will work well.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I got the lm324 and built this circuit (original from cjk2), the white section is modified (in Paint ) :
No, that does not work! I have tried adjusting both variable resistors, and haven't found a stability point (the levitated magnet bounces up and down couple times and then sticks to the electromagnet). Any ideas why it does not work??
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The gain (ie, change in output voltage per unit distance moved by the levitation target) of the phototransistor detector is probably far higher than the original Hall effect sensor, so the compensator can't cope. Uzzors obviously got it to work, so he should know how to modify the compensator to account for this.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
uzzors, I see you also used light beam to detect object's position. Could you please explain the changes you did to the circuit and how you got yours working? Thanks.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I actually based my circuit around Barry's Magnetic Levitation . By the sound of things, you will need to adjust the compensation network, or just build a different circuit. 10K and 10µf are miles from what I had to use, you could try 150K and 100nf first. If that doesn't work, check my site.
I just added the Magnetic Levitator , so check it out if you need more guidance. You seem to have all the parts handy, just use a potenimeter to simulate the reference detector, if you don't have two IR detectors. Tell me how it goes!
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
uzzors wrote ...
I actually based my circuit around Barry's Magnetic Levitation . By the sound of things, you will need to adjust the compensation network, or just build a different circuit. 10K and 10µf are miles from what I had to use, you could try 150K and 100nf first. If that doesn't work, check my site.
I just added the Magnetic Levitator , so check it out if you need more guidance. You seem to have all the parts handy, just use a potenimeter to simulate the reference detector, if you don't have two IR detectors. Tell me how it goes!
Thanks for that circuit. I can't seem to get the damn thing to work , I built the circuit exactly as it is on your page, except I replaced the reference detector with a potentiometer (10kOhm, if that matters). I tried levitating a magnet and a metal nut, I also tried both bipolar and MOSFET output transistor, nothing seems to make difference. It is always exactly the same, as soon as you bring the object close to the light beam, it starts vibrating and bouncing around, and when you release it, it sticks to the electromagnet. Maybe I have some weird photodetector, because the "linear" object position region is very small (maybe half a mm). If everything else fails, I'm going to find some Hall effect sensors and build that version instead.
EDIT: Do you think this will work for the Hall sensor version? (I'm especially not sure about hysteresis of this device and if it is wanted)
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
Don't give up so easily! Mine behaved in just the same way until I got it figured out.
Try adjusting the poteniometer so its output voltage is exactly what the output from the beam detector is. Then put your hand in front of the beam and it should turn off.
Now that that is working, how heavy is the object you're levitating and does it block the entire beam? Its too heavy if it should fall after fluttering, and if its too light it will get sucked up. Find something that is just in between.
Once you've done that, the only room left for error is the lead compensation network. Try different resistor values, check here for more info.
You should be able to get it working, as it sounds like you're pretty close. Good luck!
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Well, so I replaced the resistors in the Phase lead network with potentiometers, got a big "fridge" magnet, and started adjusting these potentiometers while adjusting my electromagnet's height, and after about a hour of adjusting it worked!! well, at least for a while. After about 10 seconds the magnet started vibrating and then fell down. Maybe after some more adjusting I can get it stable but just for this only object. Just a little different magnet and is totally unstable without re-adjusting. Edit- Now I tuned it stable. The output transistor is getting hot, probably operating in linear mode, here the tl494 comes for help (I do not have any more time right now, will play with it tomorrow)
Registered Member #71
Joined: Thu Feb 09 2006, 08:23AM
Location:
Posts: 63
Just out of curiosity as to just how unstable these things get, I built a "bare bones" levitator, which doesnt take differences of any signals nor have a compensation circuit. It uses a laser diode and LDR to sense the object's position. So basically... LDR-->transistor (turns on when no light) --> drives mosfet --> coil.
Sure enough, it is unstable as heck, and the object behaves like a woodpecker, slamming against the electromagnet before falling down then slamming on it again etc. etc.
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Magnetic levitation
) :
(the levitated magnet bounces up and down couple times and then sticks to the electromagnet). Any ideas why it does not work??
well, at least for a while. After about 10 seconds the magnet started vibrating and then fell down. Maybe after some more adjusting I can get it stable but just for this only object. Just a little different magnet and is totally unstable without re-adjusting.