University Project..Need some help

Discussion in 'The Projects Forum' started by martgreg, Mar 24, 2008.

  1. martgreg

    Thread Starter Member

    Mar 24, 2008
    17
    0
    Hi guys !!!

    I was wondering if anyone could be kind enough to give me some ideas or inspiration, guidance direction ..

    I want to make a personal fan ...After plugging it in, i would like it to be started up buy spinning the fan blades. Stopping it buy grabbing or impeding the blades...

    the blades are soft and moving slowly..so there should be any loss of limbs...:)

    so i thought i could use a centrifugal switch, or 2 or three mercury switches connected at angles....

    I am a complete newb when it comes to electronics so anything more than connecting a few off the the shelf products and soldering them together will be a challenge for me so as of right now my goal is simpler the better....


    right now I am trying to gather info and find out as much info as possible...

    Right now I dont know where to source parts or even the correct names for what I am looking for

    I have a little over a month to complete this project and time is as usual of the essecne (sp)

    So any info would be great..

    thanks in advance
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    The greenies won't let us use mercury switches any more. You could try an accelerometer. Not sure how one would couple signals & power between the rotating bits and the stationary bits. Perhaps a custom wound transformer on the fan shaft would suffice. (Could be quite a challenge for a beginner.)

    Another approach might be to use an encoder of some kind on the shaft of the fan. Signal out from the encoder would trigger power on, and lack of signal would trigger power off. If a quadrature encoder is used, one could have a reversible fan.

    Some terms for Googling:
    "accelerometer"
    "shaft encoder"
    "quadrature encoder"
     
  3. martgreg

    Thread Starter Member

    Mar 24, 2008
    17
    0
    I didnt know they got rid of mercury tilt switches...

    however when you brought up the fact of connecting between moving and non moving parts it got me thinking , i have to consider that now.. originally i thought i would take care of that later......

    is there a kind of switch that stays on when it is being made to spin .. like a small wheel connected to a micro switch that is in the on postion when it is spinning around and off when it isnt....

    or how about a simple motion detector...ie a eye that detects a ring of black and white squares that when spin are moving and when stopped they are not...... is there anything like this...

    simpler the better :)
     
  4. Pich

    Active Member

    Mar 11, 2008
    119
    4
    The switch you are talking about is called a plugging switch used for industrial puposes but that may be expensive. Any micro swith will do for the setup below.
    You could use a rotating magnet with a steel plate coupled but not touching the magnet. The steel plate would be free to move a few degrees, which in turn would make a switch. The idea would be that the motor would be spun by hand the magnet moves the steel plate making the switch, then the motor would keep running because the switch applies power to the motor. The switch would stay closed because the motor is now rotating. To stop it all you would need to do is hold the fan the steel plate would relax come of the switch and power would come off the motor.
     
  5. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    Use a current sense circuit to detect when the motor is blocked and have it shut off the motor.

    Use a voltage sense circuit to detect when the unenergized motor is being spun.
     
  6. martgreg

    Thread Starter Member

    Mar 24, 2008
    17
    0
    Thanks pich... this sounds like somehing I could manage ... however i dont really get what you are trying to explain.. do you have any apllications that this is used on already.. so I can see it in action?? or get a better understanding of what you mean....

    thanks
     
  7. martgreg

    Thread Starter Member

    Mar 24, 2008
    17
    0

    I take it these will have to be built by my self.. right.. these aren't just off the shelf deals......

    do you know of any products that use this already ?


    i am not being lazy or lame its just I need to figure out how to build these things as well as all the other parts...


    thANKS mrmeval

    it has to be a visual model so it has to look good....:) AND WORK TOOO.... AHHHHHHHHHHHHHHHHH
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
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    As a point of curiosity, since this is a "University project", what course is the project for?

    Is the fan AC or DC...what voltage/current?
    What do you want to happen if the fan is manually spun the direction opposite of the running direction?

    Ken

    Added:
    "as well as all the other parts..."? Is this just part of a bigger project?
     
  9. martgreg

    Thread Starter Member

    Mar 24, 2008
    17
    0
    Basically I am studying industrial design...This means come up with a "cool" concept that is basically feasible, work out most of the general problems... articulations, Human factors , ergonomics etc... then create an aesthetically appealing model/product.

    All the tricky stuff is meant to be ironed out by engineers...

    so technically i don't have to do all this stuff but enjoy sleepless nights and shooting myself in the foot.. plus i learn a little aswell. and if i get it to work i will be very hapy :)


    at the moment i dont mind ac or dc.. whichever is is "easier" voltage current would be 120 volts 60 hz..just a basic motor or similar you would find in a regular box fan...

    ideally if it is spun the other way i want nothing to happen... but if i have a jerry rigged circuit/system.. then i can myself figure a way of preventing in from moving backwards... but ideally nothing should happen.

    I am more type of person to think about it in a mechanical way by tripping micro switiches etc... and am not very confident in my electrical ability and the time frame I have... i would love to find a simple solution that i could but the parts from mouser or similar and just connect a few parts...or if it is possible find a hobbyiest that can do it real quickly for a fair price.... but i want to try the learning diy route first...

    please let me know if you guys have any questions.

    we can do this :)
     
  10. martgreg

    Thread Starter Member

    Mar 24, 2008
    17
    0
  11. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Your first description was a fan with "the blades are soft and moving slowly", that you could stick your finger in without injury. This is not a "boxer" fan or anything like "most" off the shelf fans. Spec'ing and sourcing this will be the first job. Then, each part after that can sort of fall in place with help from the forum. :)

    Ken
     
  12. martgreg

    Thread Starter Member

    Mar 24, 2008
    17
    0

    I agree that I need to spec the motor first, which I will in the next few days after i conduct some more tests with real size blades (not same material as final.) I have to machine them out of high density foam.

    however the motor i am using now slows down alot when i increase the pitch on my tests blades so my tests should give me more info to work with..


    thanks every one for all your help so far i will keep posting...

    :( peace
     
  13. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    I liked the current sensor idea myself, when an electric motor is stalled (stopped) it draws maximum current. Make an electronic breaker setup that has a pushbutton reset and you're good to go.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Many years ago, we had a small portable fan that was shaped quite like a blimp, where the blades were attached to the "nose" of the blimp. The three fan blades were made of a light gray flexible vinyl material, and were nearly circular. Each blade fit into a curved slot in the "nose", giving them a slightly concave curvature towards the front. The curvature served to make the blades somewhat more rigid, but more importantly gave the blades a slight airfoil shape. I don't recall precisely what the angle was, but it was rather shallow. When rotating, the centrifugal force kept the blades perpendicular to the direction of rotation.

    The construction of the fan hub and DC motor rotor was lightweight, so there was little inertia, and the speed of the fan was pretty low as well. The blades had no guard; none was necessary.

    The blade material had a similar thickness and resiliency as those anti-electrostatic vinyl mats used on electronic workbench stations.
     
  15. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    I remember that type of fan mounted on the dash in cars in the 50's, before air condition was available...rubber blades and no guards. Maybe J.C. Whitney still has them. ;)

    (Am I dating myself?)

    Ken
     
  16. Pich

    Active Member

    Mar 11, 2008
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    4
  17. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Yes. There are lots of things like this. Once again - try a Google search on "shaft encoder," and/or "quadrature encoder."
     
  18. Ganglia

    New Member

    Mar 26, 2008
    2
    0
    to me it looks like Pich has given you the way already... so let me explain.

    what you need are these.

    http://parts.digikey.com/1/parts-kws/magnetic-switch

    put small magnets into the fanblades that cross the exact same point (radius from axel) where you place the switch... the more blades / magnets and the closer you place magnets/switch to the fans axel, the better the 'sensitivity' of the device

    when you spin the blades, the magnet comes into range of the switch, that close a simple circut and powers the motor causing enough motion for the next blade to come into range... and so forth.

    stopping the blades at a position where the manget is out of range will break the circut and the spin stops.

    this do require some testing of the sensitivity, since too high sens will make the fan difficult to stop and very easy to activate.

    all you need then is:
    the fan housing
    a psu
    a motor
    the switch
    and appx. 3 magnets.

    tadaa... and here is a nice little drawing for you and your engineers ;)
     
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  19. SgtWookie

    Expert

    Jul 17, 2007
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    I'm afraid the magnetic switch won't work very well.

    1) They won't handle very much current before the contacts either weld together or burn open.

    2) Once the contact is made, the entire frame of the motor will become magnetized due to the field windings. Depending upon the orientation of the magnetic reed switch, this will tend to keep the reed switch either open or closed.

    3) The magnetic field caused by the current flowing through the windings of the motor will become much stronger when the motor is being held in a "stalled" condition than when it is relatively free-running.

    There may be a possibility of it working IF:
    1) The reed switch is used to energize a relay's coil, where the relay's coil is very high-impedance, or perhaps used to drive the gate of a MOSFET or IGBT.
    2) The magnetic switch is oriented very carefully so that the motor's magnetic field has a neutral effect upon it, no matter whether it is free-running or held in a stalled condition.

    BTW, Allied Electronics carries reed switches for about half what Digi-key is charging for them.

    Electronic Goldmine has some interesting reed switches that are tiny, and 2/$1 - along with an assortment of reed switches for a couple of bucks.
     
  20. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
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    My two cents:

    1. Reflective or transmission IR sensor: Non-contact sensing of blade/hub movement with "minimal" ambient light interference.

    2. AC coupled output from IR sensor: Provides only pulses with moving blade/hub.

    3. Missing pulse detector: Output indicates stationary or moving blade/hub.

    4. Delay: Allows motor to start and reverse direction of blades if manually spun in the wrong direction.

    5. Motor driver: Turns motor on when blade/hub motion is detected, and off when blade is manually stopped.

    No details...just a concept. :) Started with an IR sensor, RC filter, and a mosfet driving a DC motor...then got carried away with "what ifs". ;)

    Ken
     
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