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  • Heart cam size

    How to calculat a heart cam shape size?

  • #2
    Nobody else seems to be helping, I'll try.

    A circle is a cam with all radii being equal length. A cam is a circle with radii of unequal lengths.

    A cam rotates and pushes some cam-follower in and out by the variation of it's radii as it turns. To calculate the shape of the cam, you make a list of what distances you want the cam follower to be from the center of revolution of the cam for each unit of turning.

    In the case of a heart shaped cam for a wiring traverse, you pick some minimum radius for the innermost extent, and some maximum radius for the outermost extent. The difference between them is the traverse distance. Since a heart-cam is symmetrical, you only have to calculate one half, the other is the mirror image.

    If, for instance, you want a 1/2" (0.50") traverse, you can calculate the length of the radius at each degree for 180 degrees. Notice that if you start with a circle of some radius and make that radius be the minimum, then you only have to add the calculated distance to the radius. Each degree gets another 1/180th of the 0.5" traverse added to it.

    So at
    0 degrees, d=0 ("d" stands for what you add for each incremental degree)
    1 degree d= 0.5/180 = 0.0027777"
    2 degrees d= 0.00555555"
    3 degrees d = 0.00833333"
    4 degrees d = 0.011111"

    and so on, adding 0.0027777" each time.

    I haven't said how big a basic circle to add these to. That's because in some ways it doesn't matter. If you start with a "circle" of radius 0", then you add 0 to each of the calculated lengths and you get a "heart" that varies from 0 radius up to 0.5".

    Why isn't it done that way? Because it's hard for the cam follower to follow it. The bigger the radius of the center circle, the easier it is to follow the variations in distance from the center.

    Looking back I realize this explanation is a modell of obscurity; it wasn't intended that way, it's just hard for me to explain without pictures or equations.
    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

    Oh, wait! That sounds familiar, somehow.

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    • #3
      Wouldn't a heart shaped cam pile more wire on one side of the bobbin than the other?
      I used to have an old sewing machine (Singer) that came with all sorts of cams to move the needle from side to side to make different stitch patterns. I bet you could buy a box of those cams and play around with them -eventually filing them down to get just the right tone. Sewing machines are amazing in that they so closely resemble a coil winder that needs to be unscrambled like an anagram.

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      • #4
        David, the idea is supposed to be that it piles more wire in the middle, but this compensates for a regular side to side traverse tending to pile more wire on the two ends of the coil.
        It would be possible to describe everything scientifically, but it would make no sense; it would be without meaning, as if you described a Beethoven symphony as a variation of wave pressure. — Albert Einstein


        http://coneyislandguitars.com
        www.soundcloud.com/davidravenmoon

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        • #5
          The point of a cam is that it converts rotary motion to linear motion.

          If you had a circular "cam" with a pushrod crank on it, the pushrod end would move in something close to a sine wave velocity - speed fastest in the middle, with lots of dwell at the ends as it changed direction. That's what DS is referring to. The side to side motion of a traverse piles up more wire where it moves most slowly. So a pushrod style traverse would pile up wire at the ends of travel.

          By changing to a cam, you get a chance to "program" the motion by making the lateral distance pushed by the cam surface be non-sinusoidal. A cam that linearizes the traverse motion to a constant movement per unit of rotation with two reverses has an inward point and an outward point, because you want the reversal at the end of the traverse to be instantaneous to keep from having a pileup at the ends.
          Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

          Oh, wait! That sounds familiar, somehow.

          Comment


          • #6
            Originally posted by Achiles View Post
            How to calculate a heart cam shape size?
            With great care?

            A heart-shaped cam is intended to impart linear back-and-forth motion to the cam follower, with abrupt changes of direction at the ends. So, there are two segments. One segment is the linear increase of radius with angle, going from minimum radius at 0 degrees to maximum radius at 180 degrees. The other segment is the mirror image of the first segment, going from max at 180 degrees back to minimum radius at 360 (=0) degrees.

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            • #7
              Originally posted by Achiles View Post
              How to calculat a heart cam shape size?
              You mean caridiod? Just use the polar quation in this Wikipedia article. For more info go here.

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              • #8
                Originally posted by Arthur B. View Post
                You mean caridiod? Just use the polar quation in this Wikipedia article. For more info go here.
                The desired cam shape is not necessarily a cardioid

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                • #9
                  how should be a football ball shape cam,making it "fat" or "slim"?

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                  • #10
                    How about a sketch, diagram, or photo of something that works? I don't think any of us hobbyists are out to steal trade secrets from you "pros".

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                    • #11
                      Originally posted by minime View Post
                      How about a sketch, diagram, or photo of something that works? I don't think any of us hobbyists are out to steal trade secrets from you "pros".
                      I liked Brad's approach to drawing a CAM the best. Made the most "technical" sense to me. Here is his post from the "Ugliest Winder" thread where he describes it.

                      http://music-electronics-forum.com/t31329-2/#post284486

                      I believe this image is the one Brad had in his post before all site images were lost a few months back.

                      Click image for larger version

Name:	Heart_CAM.jpg
Views:	1
Size:	65.9 KB
ID:	832743

                      Here is an image of one I made in SketchUp (free CAD drawing software) for a 7/16" bobbin height bringing the benefit of digital accuracy to the base CAM shape drawing.

                      Click image for larger version

Name:	CAM Layout in SketchUp.JPG
Views:	1
Size:	131.5 KB
ID:	832726

                      The overall size of the CAM is not important other than it has to be a satisfactory fit on your winder. However, the spacing of the concentric circles is important and is the
                      = (bobbin height ÷ (number of segments ÷ 2))
                      = (7/16"" ÷ (24 ÷ 2))
                      = 7/192" or .036458"

                      Hope that helps a bit.

                      The segments here were just Brad's 15°. 360° ÷ 15° = 24 segments. The number of segments equates only to resolution of the CAM shape. More segments equals higher resolution. I found that 15° worked great as it was as fine a resolution as you could accurately shape by hand in any event. This CAM shape produces a flat coil.

                      Hope that helps a bit.
                      Attached Files
                      Last edited by kayakerca; 03-10-2014, 01:10 PM. Reason: More detail to satisfy my need for anal level accruacy. :-(
                      Take Care,

                      Jim. . .
                      VA3DEF
                      ____________________________________________________
                      In the immortal words of Dr. Johnny Fever, “When everyone is out to get you, paranoid is just good thinking.”

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                      • #12
                        Originally posted by Jim
                        Here is an image of one I made in SketchUp (free CAD drawing software) for a 7/16" bobbin height bringing the benefit of digital accuracy to the base CAM shape drawing.

                        cam-layout-sketchup.jpg

                        The overall size of the CAM is not important other than it has to be a satisfactory fit on your winder. However, the spacing of the concentric circles is important and is the
                        = (bobbin height ÷ (number of segments ÷ 2))
                        = (7/16"" ÷ (24 ÷ 2))
                        = 7/192" or .036458"

                        Hope that helps a bit.

                        The segments here were just Brad's 15°. 360° ÷ 15° = 24 segments. The number of segments equates only to resolution of the CAM shape. More segments equals higher resolution. I found that 15° worked great as it was as fine a resolution as you could accurately shape by hand in any event. This CAM shape produces a flat coil.

                        Hope that helps a bit.
                        This is how I've gone about designing cams, and it works well. That's a great explanation of the math.

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