Robotic arm select servo motors

[efirvida]

Hi i?m designing a robotic arm based on this idea of the [NOVABOT][1] I only want to change its structural parts by aluminum tubes. In this design [3D][2] model it use the servo hs-311 wish have a max torque of 3.7 kg/cm, and its made of some plastic material.

I made my calculations following [this url][3] and made a excel that I append here... the mass of my design have been taken from iProperties of Autodesk Inventor, so they are in mass units not in weight. And I?m dismissing the mass of the joints (m5,m6) to have a first idea of the values, because I dont have the selected motors.

And my problems is that I think I?m missing something here because the it results in a very high torque motors, for this simple design.


[here is my excel][4]


  [1]: https://www.behance.net/gallery/47856101/NOVABOT
  [2]: https://grabcad.com/library/novabot-industrial-robot-design-concept-1
  [3]: http://www.societyofrobots.com/robot_arm_tutorial.shtml#joint_force
  [4]: https://mega.nz/#!XRwDmbQR!jY_BNDgnkUeu2V4_tonrNdlxFQoix7zs1SRXicYOdSQ