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I need help building a solenoid controled by a rheostat

Adeboye Thompson

Oct 20, 2015
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I am trying to build an electromagnet that I can increase or decrease its magnetic force using a variable resistor or some other means. The solenoid should be about 33inches long. I have access to copper wire and I can wind the wire easily also depending on the recommendations I get. Please I will appreciate any help I can get in terms of suggestion for the construction, wiring anything. Thanks
 

BobK

Jan 5, 2010
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What are you trying to do? Are you going to try to control the position of the solenoid by controlling the current? This will not be very efficient or accurate. A better solution might be a linear actuator, which is a motor and gearing that move in a line.

Bob
 

Adeboye Thompson

Oct 20, 2015
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Thanks a lot. How can I get access to this linear actuator? I am trying to use the solenoids to alter weight of touch for my piano.
 

BobK

Jan 5, 2010
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Okay then, it sounds like you want to vary the force on the solenoid, not the position, so a linear actuator would not be appropriate. Why 33 in long? That sounds rather huge for your purpose. Can you explain in more detail what the mechanics look like? Do you have a drawing of your design?

Bob
 

Adeboye Thompson

Oct 20, 2015
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I dont have drawings yet. In fact I don't know how to build a solenoid. I have access to copper wire and I have access to someone that can spun the wires for me. I am using it for a piano. I want to be able to increase the weight of the keys by turning a knob like you do with a volume control. Thanks Bobk. I really appreciate an suggestions you might have. I also dont mind doing some technical drawings of my keyboard construction. The solenoid will be places behind the rows of keys. Sorry our power situation here in Nigeria is horrible so I am usually able to respond usually only when our power comes on. Regards
 

duke37

Jan 9, 2011
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I do not think that you need a solenoid. You could fix a bar magnet to the underside of each key and a long U shaped electromagnet the length of the keyboard to repel the key magnet.

A long solenoid will have a strong magnetic field at each end and very little in the middle.
Repulsion rather than attraction should be used to prevent key lock down.
 

Colin Mitchell

Aug 31, 2014
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You need to supply diagrams and then we can tell you to add a transistor so the rheostat (pot) will work.
 

Adeboye Thompson

Oct 20, 2015
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vlcsnap-2013-09-05-01h14m54s24.png
This is a sample of the keyboard. I want to put the magnet at the end of the keys and I think it needs to attract. When the player presses the key they have to overcome the electromagnetic field. It kind of gives the feel of opening a valve as is in a mechanical organ or tracker action organ. Thanks guys, I really appreciate all your contributions and I want more. Regards
 

Adeboye Thompson

Oct 20, 2015
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I initially placed a bolt at the ends of the keys and a magnet bellow the bolt. I also placed some felt pads on the magnet to reduce the noise of the bolt when it hits the magnet. I just want to be able to increase or decrease the electromagnetic field to vary the intensity of the pull of the magnet or solenoid on the bolt. I also feel a solenoid might be stronger than a regular magnet.
 

duke37

Jan 9, 2011
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So, you are opening the magnet gap when the key is pressed. The key will go down easier as the key is pressed due to the attraction getting less as the gap gets larger. This is different fom the organs I have played where the key becomes harder as the ranks are added.

If you wish to use an electromagnet with blocks of iron on the keys, then a long channel with one winding on it for the entire length of the keyboard would suffice.

You could use a permanent magnet on each key and a strip of iron beneath which can be raised or lowered to adjust the force.
 

Alec_t

Jul 7, 2015
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.... or you could try a mechanical approach. Looks as though there's room to accommodate a dowel/tube the length of the keyboard with a respective hole drilled diametrically through the dowel/tube at each key position to receive a short length of springy wire which bears down (up?) on the key to exert a force controlled by the angle of axial rotation of the dowel/tube. A lever or servo would set the angle.
 

Adeboye Thompson

Oct 20, 2015
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Thanks I really apprecitae all your responses. duke37. I agree with you that keys on a tracker action organ get heavier as you add ranks but I think the weight of the key decreases as you press down on the key if you are not adding new ranks.
Alec_t I don't un derstand your suggestion but I will try to read it again or share with someone with a mechanical background. Maybe they might be able to explain to me. I am concerned about the construction of the solenoid. When I made one and connected it to a battery it worked but was getting really hot really quick. How can I avoid this and still get strong magnetisim?

Thanks so much guys
 

duke37

Jan 9, 2011
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Relays are thirsty beasts and get hot. They are designed with the minimum gap to do the job to keep the dissipation as low as possible. In your case you want a considerable force over a fair distance.

A solenoid does not concentrate the magnetic force, it just sprays out the end. A better configuration is a U shaped core, attracting an iron plate extending from one pole piece to the other.
To cover the whole keyboard, you could take some square steel pipe and cut one side off to make the core. The coil could be wound on the base or two coils could be placed on the legs. You will need to measure the ampere.turns to get the force you want.
 

duke37

Jan 9, 2011
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As an alternative to a spring in Alec's suggestion you could use a bar magnet. They would not need a power source.
Some experimentation to find the best or simpest solution would be needed.

Edit: and be friction free
 

Adeboye Thompson

Oct 20, 2015
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Thanks for the picture Alect_t. Please will you mind also sharing the circuit? I hope I can find bar magnets here in Nigeria. Its always a struggle getting anything here.
 

Adeboye Thompson

Oct 20, 2015
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Some pictures from my pedal board construction. Maybe the magnets might also work here?
 

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