4 Replies Latest reply on Oct 24, 2018 12:08 PM by M. B.

    Why do these gears move in the opposite direction only in animation?

    Jacob Murray

      I have set up a screw and a couple of gear mates so that the jaw in the screenshot below closes when the middle gear is turned clockwise. Everything works fine in the model window - I move the jaw up and down and the gears move in the correct direction. In the motion study (number 5 in the assembly file), I can see the gears turning the correct way in each frame, yet when I make the animation they seem to turn in the opposite direction for some reason. I have set the frame rate to 60 to see if it might have been caused by missing frames somehow making it look like it was turning the opposite way, but even at 60 frame with no compression the middle gear goes counter-clockwise.

       

      Does anyone know what would be causing this and how to fix it?

      Capture.PNG

        • Re: Why do these gears move in the opposite direction only in animation?
          Dennis Dohogne

          Jacob,

          Nicely done!  The video looks great.  I have not downloaded and opened the zip file, but I suspect the issue is a speed issue or an optical illusion.  Try slowing down the rotation speed of the driving gear and see if that makes a difference.

          • Re: Why do these gears move in the opposite direction only in animation?
            Josh Brady

            100% it's a visual anomaly.  How many revolutions do the gears appear to turn?  During the whole video they look like they're only turning about 1/4 to 1/3 of a turn.  However, your shafts make many revolutions, as evidenced by the number of times the thread start passes by.  Also, examine the hex cut into the center of the middle gear.  It should turn just as smoothly as the rest of the gear, but instead it jumps all over the place, out of sync with the teeth.

            • Re: Why do these gears move in the opposite direction only in animation?
              M. B.

              I went through this several years ago with a video that had so many moving parts I had to write an excel formula to figure out the optimum frame.  It’s the same problem movie makers had with black and white western movies where wagon wheels appeared to rotate backward.

               

              To look smooth and appear to rotate in the right direction:

              -The gears must rotate < 360 / 14t / 2 per frame

              -The hex. must rotate < 360 / 6 / 2 per frame

              -The threaded leadscrew must rotate < 360 / 1 lead / 2 per frame

              So, each frame when gears, hex. and thread are rotating must satisfy all the above.  The more moving parts you have with different teeth/flats/threads, the more frames you'll need.  Linear frame movement doesn't have this limitation.

                • Re: Why do these gears move in the opposite direction only in animation?
                  M. B.

                  To expand a little further, these deg. values would work also.  For lots of moving parts, figuring out the optimum rotation angle per frame with the technique below is tedious but once determined it can greatly reduce the number of frames required.  That's where excel helps.

                  Hex –      0 < 30 deg

                                 > 60 < 90 deg

                                 > 120 < 150 deg

                                 > 180 < 210 deg

                                 Etc.

                  Gear –    Same concept as shown with hex. above.

                  Thread – Same concept as shown with hex. above.