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Starting DC motor by squeezing handle

Discussion in 'Sensors and Actuators' started by homer2121, Jan 2, 2016.

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  1. homer2121

    homer2121

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    Jan 2, 2016
    Hi, I am a newbie when it comes to electronics and circuits but would like help with an experiment I am working on.

    With a round handle (aprox 15-20mm diameter) I want to be able to send a current to start a small DC motor based on how hard the handle is squeezed. I don't want the motor to run when the handle is squeezed say 5,6 or 7 on a scale of 1-10 (will take some trial and error to figure out exactly how hard that is) but if the handle is squeezed harder or lighter than that range I want it to run the motor. I am thinking I would also need a switch to turn it off so when nobody is holding it the motor isn't running. If it isn't possible to start the motor when squeezed both lighter and harder than the range then I at least want it to start the motor when it is squeezed harder than the desired range. All of the components would need to fit inside the handle which will be 10-12 inches long (so all stacked on top of each other).

    As I mentioned I have very little knowledge in this area but I have some battery holders with attached leads and a DC Motor. Once I get a switch and whatever else I need I really have no idea how to connect it all together. Also, based on some of the research I have done I came across piezo film sensors and thought that could possibly be wrapped around the handle but I was wondering if that is the best way to do it or if there was other options. It needs to be able to withstand a little bit of wear and tear. It won't be thrown around but could be dropped occasionally.

    Any suggestions??

    Thanks
     
  2. BobK

    BobK

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    Jan 5, 2010
    I don't think you will get very good answers with the vague description you have given.

    Is this handle something that deforms when squeezed, or is it a solid piece of tubing that does not deform, or is it two pieces that come together when squeezed like a hand brake on a bicycle, or something else entirely?

    A better description and pictures would help.

    Bob
     
  3. homer2121

    homer2121

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    Jan 2, 2016
    Sorry about that. The handle is to run a fan when squeezed. So picture a round broom handle shape about 2cm in diameter and about 10-12 inches long. The handle is solid piece that will not deform when compressed. I may put a rubber grip over top but I just want it to detect the amount of pressure when it is squeezed and start the motor when it is squeezed either below or above the desired range. When it is squeezed within the desired range I do not want the motor to turn on. It needs to be able to detect the pressure almost everywhere on the handle which is why I initially thought I would need to wrap the handle with something like the piezo film. I do not have a picture as I have not built it yet. Does this make it more clear??

    Thanks
     
  4. homer2121

    homer2121

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    Jan 2, 2016
    It has been suggested to me on another forum to interface with a microprocessor and that I should try arduino as I have limited knowledge. Does anyone know if arduino would teach me what I need to know to accomplish this?

    Thanks
     
  5. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Lets see if I understand this... someone picks up the handle and the fan motor starts. If they squeeze hard enough the motor stops. If they squeeze a little harder the motor starts again. The fan motor is stopped in between these two levels of squeeze. If they lay the handle down you want a switch available to turn the fan motor off. Presumably this same switch turns the fan motor on initially. Is this some sort of psychology lab experiment?

    Anyway, the problem is finding a suitable "squeeze sensor" and interfacing that sensor to the motor. I think I would use a short length of largeish diameter plastic tubing, seal the ends and add a linear differential pressure transducer to the bottom end, one input exposed to air and the other to the inside of the (slightly) compressible plastic tube. You may have to fill the tube with an in-compressible liquid such as water or mineral oil to obtain sufficient pressure variations. An Arduino or other small microprocessor can measure the transducer output to determine the amount of "squeeze" and drive the motor appropriately.
     
    Last edited: Jan 3, 2016
  6. davenn

    davenn Moderator

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    before you get to any sort of micro controller, you need to sort out the handle

    My first thought would for it to have two conductive strips and the act of squeezing more or less tighter changes the resistance between the two of them via the hand
    there may be dual layer conductive layer materials that could be used
    Getting this sorted is definitely your first mission, as your project isn't going anywhere without it


    D
     
    hevans1944 likes this.
  7. Martaine2005

    Martaine2005

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    Ok, I admit I am completely confused here...An Arduino and a fan inside a "broom" handle diameter tube?
    Anyway, I am with @hevans1944 with air.. Adjusting it to turn on and off is easy. The bit in between will take some playing with..
    I found a "squeeze" switch. It will basically force air down a plastic tube. But wont fit inside the tube either!
    Have a look at Euro syphons. They have two buttons for more or less air.

    [​IMG]
     
    hevans1944 likes this.
  8. hevans1944

    hevans1944 Hop - AC8NS

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    I didn't know you could buy these off-the-shelf. Could you provide a link? Does it activate a switch in the box or some sort of pressure transducer? Looks like it could do a nice job of measuring squeeze pressure. Pretty blue color too! What are these normally used for? What do they cost?

    Edit: Umm. Nevermind! Google "squeeze switch" and a whole bunch of stuff shows up.
     
    Last edited: Jan 3, 2016
    Martaine2005 likes this.
  9. Martaine2005

    Martaine2005

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    Yes Hop.
    The picture I posted was from a 'special needs' web site without further info on the switch. Just a hefty price!
    But as far as I can make out, they are all just diaphram pressure switches like boiler (furnace) switches.

    Martin
     
  10. hevans1944

    hevans1944 Hop - AC8NS

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    @homer2121 hasn't replied to our comments yet, but I can't help but notice this is yet another example of a newbie posting their "solution" to a problem without telling us exactly what the problem really is. For example, stating that the handle must be incompressible, like a broom-stick, without saying why this is necessary. Why is a stick handle necessary or desirable? Why not a spring-loaded pair of squeeze-grip handles? Why not a ball you hold in your hand and squeeze? What's wrong with a little compressibility, enough to effect an internal pressure change from the concomitant reduction in volume with pressure? And how big is that fan? Is it located inside the handle? Is the motor inside the handle with the fan an external attachment to the motor shaft? Is this contraption powered from one or more energy cells stacked inside the handle? Since the motor is already on hand, how much voltage does it require and how much current does it draw? What are the physical dimensions of the motor and battery holder (with leads attached)?

    It would be so much easier if folks would tell us what problem they are trying to solve, rather than their "solution" that may or may not be appropriate.

    Hop
     
    Last edited: Jan 3, 2016
    Martaine2005 likes this.
  11. hevans1944

    hevans1944 Hop - AC8NS

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    A MEMS pressure sensor is quite inexpensive, but they usually do require some signal conditioning. See attached datasheet.
     

    Attached Files:

  12. Martaine2005

    Martaine2005

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    I hear ya Hop, but it does keep the grey matter ticking
    I also think you nailed it!! Air switch..
    Hospitals use them all the time too rather than leaving the inferm with wires..
    Now the trick is not turning on in the central points.
    But as you said, the OP hasn't responded yet..

    Martin
     
  13. hevans1944

    hevans1944 Hop - AC8NS

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    @Martaine2005 not turning on in the central points is easy: it's called a window comparator. But it does need an analog signal representing the squeeze pressure. I was thinking of thick-walled large-diameter Tygon flexible tubing when I wrote my first response. If you fill this with water or mineral oil and couple it to a MEMS pressure transducer on one end, with the other end sealed, then it should produce enough of a change in pressure when squeezed to drive the MEMS transducer full-scale. You could try it without a liquid inside, but air is so compressible that there would be relatively little change in air pressure until the tube was squeezed almost flat. You want a very small change in internal volume to produce a large change in pressure. Might have to worry about getting all the bubbles out when filling it though.

    I think I have an application for this broomstick/motor/propeller device. With suitable battery, motor, and propeller all integrated into the handle, you pick it up and hold it overhead at arms length (like the Statue of Liberty in New York Harbor). The motor begins to wind up and lifts you off the ground. When you are at a suitable altitude you squeeze harder to stop the motor and allow you to descend. If descending too fast, you apply your panic grip to restore lift. Too late for Christmas giving, but someone should talk to Mattel about marketing this.
     
    Martaine2005 likes this.
  14. Martaine2005

    Martaine2005

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    Sir Hop Poppins comes to mind...:p Or should that be Inspector Hop..
    And then the fan stops and a camera pops out for the SELFIE!!



    self.png
    Martin
     
  15. BobK

    BobK

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    Yes, but we need another propeller at right angles to stop the counter-rotation of the person using your device. Or perhaps multiple counter-rotating propellers like a quad-copter.

    Bob
     
  16. hevans1944

    hevans1944 Hop - AC8NS

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    Actualy, the counter-rotation from the reaction torque on the propeller is a "feature" of this new toy. It allows a full 360 degree panoramic view. Rotation speed is varied by extending the other arm and legs to change the moment of inertia about the ascension axis. See photo of Peggy Fleming below demonstrating an early prototype. Please note that the lifting device in Peggy's left hand is hidden in this photo because she was using a secret beta prototype. Foot ballast was necessary to maintain vertical orientation and assist in changing the rotation rate about spin axis. She later went on to other amazing feats showing extraordinary skill and determination, but chose never again to use the "lifting stick" which subsequently vanished from sight for lack of a commercial sponsor. Ms. Fleming was married two years after this photo was taken (breaking my heart) and has lived happily ever after. She was (and is) a real sweetheart.

    [​IMG]
     
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