electromagnetic button/carriage array controlled by midi

Discussion in 'The Projects Forum' started by wooly239, May 12, 2013.

  1. wooly239

    Thread Starter New Member

    May 12, 2013
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    Hi there - Ive been searching and found this website - spent some time browsing and also searching within it.

    It looks like a lot of knowledge and experience here so I thought I'd join and ask for some expert advice and help.

    This is my first post and to be honest I know so little about practical electronics (though know basic terms and generally understand the principles behind how an electromagnet works - i did some basic soldering once and can follow instructions well) and that I foresee a steep learning curve.

    However I am prepared to learn and willing to take advice :)

    I know there are a lot of steps in the project, so I guess I am asking if it is possible to build, what kind of estimate cost would the parts be (max $2000), and can a newbie like me with help from members here actually have a chance of being successful


    The Project: a controlled electromagnet array of pressure buttons mounted on a carriage that travels along a pair of straight trammel type rods.

    My aim is design and build an array (minimum 4 / max 16) of fingertip (1/2") sized 'buttons' that can be actuated by electromagnets to deliver pressure of approx 3 pounds (perhaps a little more), displacing the button 'head' about 1/2" toward 'target areas' that are about 1/2" directly below.

    The buttons should be able to operate singly or simultaneously

    The buttons will be side by side perhaps 1/8- 1/4 inch apart

    The buttons will also be mounted on carriage that is mounted on two slide rods so the carriage can move along the slide rods (perhaps with a screw thread cut into the rods for a drive, drive belt, or some other means of moving the carriage to certain points back and forth on the rod trammel say within accuracy of 1/8")

    The button response time should be a fast as practicable (at least 10 ms ) _ I think perhaps with some sort of spring return for each button that retracts the button once the electromagnet is turned off

    The carriage response time should be about 250-500 ms

    I'd like to control the system (and this is a first set of ideas and I'm open to suggestion) with something like arduino and USB using midi controller data

    Using midi data is a requirement but the arduino is not

    So im looking for a reality check on the possibility, a shopping list and some technical help on programming.

    I have access to a workshop for metal and computers for programming.

    I am looking forward to hearing from you all

    Thanks in advance

    W
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Welcome to All About Circuits and I'm certain that you have found a great site to help guide you through any questions you may have on electric and electronics circuits.

    For your first post, that is a fairly lengthy one to have to read through. While that is better that a short one liner that hardly describes the problem, it is best for you to state up front what exactly you are attempting to do in a concise statement. Once we get the big picture we can then get down to the details in a subsequent follow up.

    Having read through your lengthy post I still cannot figure out what you are trying to do.

    So we have some kind on mechanical plunger that hits buttons and send out MIDI data?

    Why do we need mechanical fingers in the first place?

    Why do we need buttons?
     
  3. wooly239

    Thread Starter New Member

    May 12, 2013
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    Hi Mr Chips

    Thanks for your response. Sorry if it was not concise enough.

    Yes we have mechanical plungers that 'are the buttons' - i.e. i wasnt sure what to call them but plunger is good.

    The plungers don't send out midi data they will be operated by it. i.e I can use maxmsp or simple midi controller data to operate on/off (I am very familiar with midi as protocol)

    We need fingers (plungers are fine, not articulated fingers, just a set of vertical plungers) because I want to depress wires at certain points along their length that will create a different wavelength from their default position.

    I suppose I can name the machine a 'player string machine' if that helps abstract visualisation.

    I have ideas about how it looks but wanted to hold off and get mechanics first then create form from function.

    Thanks again

    W
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    No. I have found it is best not to "hold off" but get the "big picture" clear up front.

    Let me see if I can get this right.

    You have a stringed musical instrument such as a guitar, violin, double bass etc.
    You want to send MIDI data to actuate mechanical fingers to hold the string down on the fret board in order to select the desired note.

    Something else is going to pluck or bow the string.

    Incidentally, this approach to describing a problem is called Top-Down Design.

    You're in luck. I happen to be a musician and I teach engineering systems design.
    There are other members here with similar qualifications who would be more than happy to assist you with such an interesting project like yours.
     
    Last edited: May 12, 2013
  5. wooly239

    Thread Starter New Member

    May 12, 2013
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    Hi again Mr Chips

    Yes you have it correctly with a few twists on my part...

    Very glad to hear that you are a musician and think it is interesting and worthwhile.

    I was a furniture maker years ago in my 20's and have a been a music technologist for almost 30 years and musician since I was a kid. I can make things out of wood to exacting dimensions
    so I intend to make a fretboard as yet with undefined number of strings. THis may or may not be flat and could even be a thick cylinder depending on how the carriage mechanism develops.
    I havent decided whether to make a sound box or use pickups for amplification, or both.

    As for the pluck or bow - I'd prefer a bowed operation. I was intending to first see if I can get one plunger system to work first then if successful, duplicate that and then think about the using the same system with some modification lower some sort of motorised rollers (variable speed) with brush material or some other appropriate coating and rosin on them to bow each string, again with on/off midi control for each

    Sorry about the inside out approach - I get the top down
    The way I think is probably problem based and I was trying to solve the problem of not having to use my hands to play the machine but to use a set of midi controllers along with additional sampling tools in a live performance context. The shape or design of course can take lots of directions and I was thinking about the playing mechanism as my first problem.

    I do hope the members find this interesting enough to help.

    Thanks again

    W
     
  6. williamj

    Active Member

    Sep 3, 2009
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    32
    Wooly239,

    I'm not a musician nor am I an electronics expert. Mr. Chips, and a whole bunch of others here are experts, and has help me several time in the past. I am however a retired industrial electrician/mechanic and the way you described the movement seems to be a little problematic.

    Using two rods and a stepper motor, with screw drive, should work for short distances, but for longer distances (like the length of a fret board) it's not going to happen in the time frame given.

    The only thing that comes to mind right now is a magnetic drive (think maglev without the lev) or compressed air. Controlling a magnetic drive way beyond me and compressed air is a whole nother set of headaches.

    Just my thoughts on the matter.

    Good luck, williamj
     
    Last edited: May 13, 2013
  7. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Yes, I agree that a stepper motor driving a lead screw is too slow.

    But, I would suggest using a stepper with timing pulleys/timing belts

    For example a 20 tooth 1/5 inch pitch pulley would give 4 inches/rev travel
    Using a 400 step motor would still give .01 inch resolution. Steppers are relatively slow speed but can reach a few revs per second.
     
    Last edited: May 13, 2013
  8. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Edit: Removed duplicate post.
     
    Last edited: May 13, 2013
  9. MrChips

    Moderator

    Oct 2, 2009
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    The seek time of the print head on an ink jet printer is pretty good.
    I agree that a belt and pulley drive is a better choice. A linear motor with analog drive can reach some remarkable speeds.
     
  10. wooly239

    Thread Starter New Member

    May 12, 2013
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    Thank you all for adding comments.
    It seems we so far have consensus on a stepper motor with pulley

    I was thinking further on the plungers and these could have hard rubber rollers as 'finger tips' that could also travel along strings when the plungers are depressed to provide a glissando function.

    The same rollers coated appropriately could also be part of the motorised brushes?

    Also one other thought - the electromagnet for the plungers - is this better that one large magnet operates for all plungers? or one each? I was thinking if there was a power consideration each plunger could have its own magnet, but for construction it may be easier to construct one magnet for all - with some form of interruption system to select which plungers actually get turned on?

    Thanks again all for responding :)

    W
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    Depends. Are you going to be playing one note at a time or is this going to be a polyphonic instrument, playing double stops, chords and arpeggios?
     
  12. wooly239

    Thread Starter New Member

    May 12, 2013
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    Yes on the second one, plyphonic with stops.
    All plungers should be able to play together or singly in melody or chords

    I will try to sketch a few basic forms (albeit without technical detail or schematics) as potential springboards for ideas for operation and function, that I think encompass the functions as described so far.

    Thanks again
    W
     
  13. MrChips

    Moderator

    Oct 2, 2009
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    Well, you have introduced an added complexity.
    If you wish to select specific notes on more than one string you will need a separate rail for each string.
     
  14. tubeguy

    Well-Known Member

    Nov 3, 2012
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    What about having the moving carriage replicate the hand position of a stringed instrument player. You can reach all of the notes needed to play various chords. You wouild need many plungers, but maybe less movements.

    How many strings are you thinking ?

    BTW - After arpeggios these days I usually need a nap. :p
     
  15. MrChips

    Moderator

    Oct 2, 2009
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    Whoa! This is getting complicated.
    On a 6-string guitar you can stretch three semitones.
    You would need 4 x 6 = 24 solenoids to replicate the human hand.
     
  16. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Yep, I know. Just wanted to throw that idea out here.
    But playing multiple notes/chords would then require maybe a separate motor pulley for each string?

    Edit: Sorry MrChips, you already mentioned multiple rails. :)
     
  17. MrChips

    Moderator

    Oct 2, 2009
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    That's the benefit of open source brain storming. You get to throw all the ideas into the hat.
    I bet we haven't seen the winning one yet!
     
  18. wooly239

    Thread Starter New Member

    May 12, 2013
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    Hey all
    Thanks for the input today.
    Yes I had envisaged something like a matrix of plungers (I think I said 16 in my first post ) but mr chips is right with the reach and yes six steps sounds right - i was thinking of 3 sets of 4 strings bass, cello, violin as a medium goal. It all depends on the length of strings for each section and wavelength that is divided up into octaves notes and harmonics .

    So a carriage that moves its reach up and down a set of two rods but with its own fixed stretched reach of plungers approximating that of a players hand

    I ll def try to get back with some basic drawings soon to reveal more clarity if that's possible.

    Thanks again
    W
     
    Last edited: May 13, 2013
  19. tubeguy

    Well-Known Member

    Nov 3, 2012
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    I realized there's an issue with the moving carriage idea.

    The spacing between notes changes as the hand moves around the neck, so the spacing between let's say 4 plungers, would have to be adjusted depending on the position on the neck. More complexity.

    Now I'm thinking the idea to have a single moving plunger for each string might be more do-able.
    A player's hand does take some amount of time to move around the neck of an instrument. As fingers on the hand do, the group of four plungers would normally stay near each other. I'm guessing the same time it takes a player to move around the neck of an instrument could be replicated this way.
     
    Last edited: May 14, 2013
  20. wooly239

    Thread Starter New Member

    May 12, 2013
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    Hi Tubeguy
    Good morning
    That's a good point.
    I was thinking that with frets the plungers only need to be between the frets to plunge so less accuracy would be needed but with shorter wavelength the notes are closer together as you mention providing another hurdle.

    What if the carriage concertina'd open and closed to provide finger stretch and compression whilst still running on two rods - each plunger could have a sub transport for short range adjustments - or am I barking mad?

    Of course conventional thinking isn't a requirement but i would like to have accuarate semitone playback - so any approach that retains accurate note frequency should be considered even if it adds complexity

    If on the other hand as you suggest there were rods for each string there is no reason why the strings could be further apart than conventional stringed instruments to provide space for the mechanism on each string if that's what would work.

    I am still not clear myself how much width an electromagnet would need per string? Perhaps this detail could or will drive the question?

    Thanks again for your input

    W
     
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