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Old Aug 26, 2003, 03:01 PM
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Cannes Mandelieu, France
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another question:did you try to make remote ones with your system?
patrick.;
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Old Aug 26, 2003, 06:13 PM
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MSC Rödinghausen, Germany
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Patrick,

yes, your question is difficult to answer. Basically I think that for any given magnet the current times the number of turns is proportional to the torque because all the magnetic flux generated by the current in the coil will concentrate in the magnet (and not in the air around it) anyway. So, if you make a coil with big diameter and 100 windings, it will generate the same torque as a small coil with 100 windings. I have made experiments and they seemed to confirm this.

Obviously you will need more energy to drive the current through the bigger coil because the wire is longer. On the other hand, if you use PIC outputs directly then the energy is limited: A PIC chip can deliver about 5V and 25mA, so the resistance of the coil has to be 5V/0.025A = 200 Ohm.

Furthermore I believe that it is best to use the same weight for the coil and the magnet. My magnets weigh 0.4g, so I use 0.4g of copper wire to wind my coils. This leads to 23m of 0.05mm diameter wire, which weighs 0.4g and has 200 Ohms.

Now, to optimize efficiency, you have to make as many turns as possible, which is done by choosing the coil shape as close to the magnet as possible. I use these longish magnets because I believe that a longish magnet generates more torque than a short one, and I wind my coils oval because that is closer to a longish magnet than a round one.

I have never used a round coil, but I try to make my coils smaller all the time and make a smaler gap between the coil and the magnet, which gets difficult quite quickly. The coil shown in the first picture is wound onto an oval Teflon core and then hardened with CA. See the picture.

I have done everything described above more by engineer's instinct that by exact, scientific calculations, although it might be quite interesting to sit down and try to calculate the torque by the basic physical rules. I have tried to find a mathematical approach for this but have failed so far, so as long as my actuators work for me (which they do) I will probably leave that aside.

Hope that helps,

Regards, Jochen
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Old Aug 26, 2003, 06:18 PM
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My winding fixture in parts (I use a layer of PE film around the steel core wires so that the CA does not stick to them).
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Old Aug 26, 2003, 06:47 PM
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Australia
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Robert,

I got my roll of wire from guiter pickup winder as Graham mentioned. I got his last roll.

Jochen,

Maybe you could answer my earlier question regarding current rating for wire sizes from say 0.02mm - 0.08mm.

Thanks

Dave
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Old Aug 26, 2003, 07:01 PM
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Thought this formula wheel might be handy for some people.

Dave
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Old Aug 26, 2003, 09:07 PM
FLB
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Montreal-Toulouse
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This thread has a lot of good information and pictures. Thanks for the ones who are sharing their knowledge.

Dave,
You're right, this formula wheel will be handy, at least for me I have found a useful "Wire sizing chart" by Park Flight:
http://www.smarttoolsinc.com/TechTip...zingChart.html

Patrick,
In fact, my Conrad link for 0.05 mm copper magnet wire came from the website you mentioned. Are you sure for the length of the "bobine" (1500 m) at 5.70 euro because on the Conrad website it's written 1500 mm which I found honestly much too short. I will probably have to go in France in 2 weeks. Maybe I can buy there some cheap plastic clocks... Hope I will have no problem to go back through customs

Thanks, Frederic
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Old Aug 26, 2003, 09:48 PM
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Thanks Fred,

thats what I was after
thanks also for your contribution

Dave
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Old Aug 27, 2003, 12:26 AM
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Cannes Mandelieu, France
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frederic.
i confirm it's 1500 metres,weight 31 gr,ref:60-75-09-33 page518.
i don't think you'll have problems with customs.
clocks are in "all at 1.70 euro" shops or others.
if you come in south of france i'll be happy to meet you.
patrick.
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Old Aug 27, 2003, 06:07 AM
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USA, FL, Fort Lauderdale
Joined Feb 2002
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Jochen,

Thanks for showing an example of your formula with all of the actual figures. It allows me to follow the formula even though my math skills are weak. In high school I was working in the metal and wood shops when I should have spent some time in math class. Skipped college and went straight into the family printing business. Thanks again.

Dave
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Old Aug 27, 2003, 06:22 AM
Sticky Shepherd
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Oxford/England
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I have added this thread to the useful thread, thread.

God it needs a more catchy name

Graham
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Old Aug 27, 2003, 07:07 AM
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Annapolis, MD/Venice, FL
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I agree with Jberg that oval coils work better than round coils for typical magnet geometries. I am currently building coils that closely match magnet clearance. This is because magnetic field strength is related to flux density and not just flux. Flux is related to the turns in a coil along with the current (Amp-turns). If the area of the coil is large, the flux is dispersed over the whole area and will have less effect on a magnet.
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Old Aug 27, 2003, 08:31 AM
Sticky Shepherd
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Oxford/England
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Also making the coil internal diameter smaller gives more turns for a given resistance so it is a win win situation.
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Old Sep 03, 2003, 09:32 PM
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Australia
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200 ohm coil specs are:

center (straw) outside dia. is 4.8mm
side outer dia. is 8mm
overall width 4mm
1160 turns
0.05mm wire
0.5 gram

3mm x 2mm magnet 0.1 gram

Remote actuator 0.1 gram

Remote actuator complete with coil and magnet 0.7 gram.
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Old Sep 03, 2003, 10:42 PM
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United States, VA, Clintwood
Joined Nov 2002
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Hey
Here is my lightest coil the whole assembly weighs 270mg.

46 or 48 guage wire from 1964 guitar pickup. I lost the pickup last year.
I think it fell in my trash can beside my building board. Since then I have moved the trash can.

5mm I.D.
2mm wide
I think around 50 ohms might have been 36 I'll have to look it up in another thread.

The magnet is either Sm or Nd one of them rare earths and 3mm x 3mm x ~ 2mm.
I had made it for use on a 6" bitplane but didnt have too much
success with the airframe or getting it to fly consistently but the rudder worked pretty good on the glide.
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Old Sep 03, 2003, 10:46 PM
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United States, VA, Clintwood
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I'm going to have to upgrade my camera seeing my picture compared to the rest of them. Sometimes I can get a decent picture out of it and other times it's really grainy.
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