• Marten de Groot posted an update 2 years, 2 months ago

    I’ve made a other servo pully.
    I hope to get soon the springs because they are needed in this design.
    Here two pictures from a mounted pully at a servo and a picture with some views from the drawing:

    • Hi Marten
      I think before changing the pullies we should agree what the mechanical requirements are for the fingers.
      In my arms I use mg996R and they can turn about 110 deg to the left and to the right (total 220). So when Gael says he can move all fingers with the exception of the middle one with an unmodified HK15298 servo which allows only 45 deg to left and right it looks like I have a lot of dead band in my setup where the fingers are mostly sluggish – and I agree with that.
      But besides the mechanical limits we have the control by MRL – and MRL lets us specify the servo range to use with the map() function.
      So in your scripts you just need to specify the mapping to be used with your servos and for perfectionists it can also be non symmetrical to still have your pullies look north when in 0 position?

      • Hi Juerg,

        Thanks for your input about this.

        The good thing to use a 180 degrees pully, is that there is less change to break any mechanical parts.
        A other good thing is, there is a higher resolution to place/hold the finger at his position.
        Have you seen my Finger Starter video ?
        Here I’m using a MG996R servo and it turns a full 180 degrees without any problems and with a good torque.
        (did you changed something with the servo’s, to get the 220 degrees range ?
        I will check tonight how many my MG996R can turn mechanical)

        In MRL all sliders will move the servo normally a max of 180 degrees.
        So this means that people can’t overkill the maximum positions.

        For some fingers I need to make the pully a bit bigger or smaller.
        I’m now printing all the part for the right hand and underarm.
        I hope to finish this soon so I can play with the Pully sizes.
        This week I hope to receive the springs to, this will help a lot.
        With the Finger Starter kit I can test the new spring configuration and I’m almost sure it will work fine.

        • Agree that individual pulley’s for your combination of servo and finger would be safest for builders. Just go 0 to 180 without having to worry about limits.
          I am rather the software guy and think – once the mechanical part looks good – I can control movements with the mapping function of MRL.
          For me the springs are rather an option to add a bit more “intelligence” to the fingers. I am imagining a linear resistor attached to the spring. In addition I would loop the connection between the servo controller and the built in potentiometer on the closing side through this linear resistor. The servo will add up position and pull and stop?
          With the help of InMoov’ s camera and google image recognition it might even be possible in some cases to calculate a servo target position that will take the items delicacy into account? Just dreaming – I know.

          • Dreaming is a good part of your life :-)

            Sounds interesting about the linear resistor position feedback and the camera / google image recognition.
            I hope to see more if you have done some tests ;-)

            About the servo pully sizes, the size is based like the http://inmoov.fr/wp-content/uploads/stl/Forearm-and-Servo-Bed/servo-pulleyX5.stl
            They will fit to a basic Futaba 21mm pully.
            Sadly these pully’s are not included with a MG996R :-(
            so they need to be ordered separate.

            The reason why I like to use these 21mm Futaba pully’s, is because the holes are closer together…
            This gives the option to make the pully’s as small as possible.

            Tonight I will make some more pictures from all pully parts.
            So it’s more clear how they will fit together.