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brettduncan (Electrical) (OP)
16 Mar 09 4:58
Good day,

I need to build a two dimensional magnetic levitation , but the problem i'm having is that the electromagnets are very sluggish in response time.

Would a ferrite core work better then normal mild steel? I'm controlling the current with a PWM signal at about 4kHz.

What other materials (for cores) would be suitable for quick response?

Thank you,
Brett Duncan
MagMike (Materials)
16 Mar 09 7:43
Ferrite cores will have a faster response time.
brettduncan (Electrical) (OP)
16 Mar 09 11:37
thanks MagMike,

I have searched extensively to try and locate ferrite rods with diameters between 15mm and 25mm in South Africa, do you perhaps now of a good source to purchase similar sized ferrite rods?

Could I also get a bunch of smaller rods and bind them together with epoxy to form a larger core? Will this work?

Thank you,

Brett
MagMike (Materials)
16 Mar 09 15:18
I'm based in the US.  Unfortunately, I do not know of a source in South Africa.

Smaller rods bunched together will work, although any spaces between neighboring rods will "dilute" the performance a bit.
brettduncan (Electrical) (OP)
16 Mar 09 15:46
Thank you once again MagMike,

I have searched extensively regarding ferrite rods? Will you be willing to help me out in getting some rods and shipping them to me. I will wire the money from a bank here to you over there.

Thanks,
Brett
MagMike (Materials)
16 Mar 09 16:44
Sorry, I won't be able to help you with that.
brettduncan (Electrical) (OP)
17 Mar 09 0:45
thanks MagMike,

Just a question regarding want I want to do. The formula that I'm using to calculate the number of turns, etc. is

V = 4.44 * N * f * Omax

where Omax = area * Tesla rating

Do you thin that this formula will actually work?

Thank you,

Brett
MagMike (Materials)
17 Mar 09 8:31
I can't say if a given formula will work.  You haven't provided nearly enough information to make a decision.  Aside from mentioning magnetic levitation, you haven't given much information as to what you are trying to do.

Formulas are just useful for describing behavior within certain parameters.  You need to have an understanding of what goes into them, why certain variables are present and, most importantly, their range of validity.
brettduncan (Electrical) (OP)
17 Mar 09 16:18
Thanks again MagMike,

Here is a break down as to what I'm trying to do.

It needs to be a two dimensional levitation system whereby a user can change the position in the vertical and the horizontal axis. Firstly, the system must perfectly levitate the object and then be able to externally (via a POT)change its position.

Please find attached my current design that I'm working on.

I will be using a DSP. The output of my DSP will use PWM (at a frequency of about 25kHz - it doesn't have to be this frequency though) that will control the current throught the magnets. That is why I will need to use a ferrite core electromagnet so that I can swtich at those speeds. I will be using Hall effect sensors as feedback for my system

My first biggest problem is designing the magnet. The formula that I posted earlier is the one that I will use for the design of the electromagnet.

Can you please give me some feedback as to what perhaps I should look out for and perhaps help me out with the electromagnet design using a ferrite core.

Thank you and kind regards,

Brett








 
MJR2 (Mechanical)
18 Mar 09 7:54
Magnetic levitation is very unstable. As you have begun to understand the response time in your electromagnets is an issue. There is only going to be one 'sweet' spot here and the forces that want to move the object out of that are much faster than your electromagnets can respond.  

Mike

MagMike (Materials)
18 Mar 09 9:59
I couldn't agree with MJR2 (Mike) more.  The magnetic interation of the side electromagnets is going to prevent any stable levitation.  The fields from the side electromagnets will travel to the center electromagnet as well as the permanent magnets in ways to prevent stable levitation.
IRstuff (Aerospace)
18 Mar 09 14:15
Is this a school project?  Student posting is not allowed.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

brettduncan (Electrical) (OP)
19 Mar 09 5:41
no this is not a school project.

 

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