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Re: RES: RES: [diy_3d_printing_and_fabrication] Servo motors

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  • Graham Stabler
    well the angular resolution stays the same as it is an angle but with a longer arm you get more movement for a given angular resolution so I know what you
    Message 1 of 8 , Feb 27, 2013
      well the angular resolution stays the same as it is an angle but with a longer arm you get more movement for a given angular resolution so I know what you mean. Adding gearing is good if it has extremely low backlash, ideally you want to stick the encoder on the output and have a really good gearbox like a harmonic drive to stop servo oscillation. You can get high res encoders fairly cheaply, there are some 16bit absolute Avago (formally HP) ones that not too horrendously expensive and some of the magnetic ones have lots of bits, not sure of the accuracy though.

      It can be done but not easy just need to do the sums and check your wallet :)

      Graham



      On 27 Feb 2013, at 15:53, "Murilo Torres" <murilo@...> wrote:

       

      Ok... got it.

       

      Well, the angular resolution decreases when you get far from the axis. Using a planetary gear box or other precision reduction is a way to mechanically multiply the resolution, and of course, sacrificing the speed…

       

      De: diy_3d_printing_and_fabrication@yahoogroups.com [mailto:diy_3d_printing_and_fabrication@yahoogroups.com] Em nome de Graham Stabler
      Enviada em: quarta-feira, 27 de fevereiro de 2013 12:37
      Para: diy_3d_printing_and_fabrication@yahoogroups.com
      Assunto: Re: RES: [diy_3d_printing_and_fabrication] Servo motors

       

       

      except he is not driving a leadscrew he want to use it on a robot

       

      Graham

      Sent from my iPad


      On 27 Feb 2013, at 15:20, "Murilo Torres" <murilo@...> wrote:

       

      It’s quadrature, so you get 8192 readings per revolution. If you drive a 5mm lead ball screw with this resolution you would get 0,0006mm precision.

       

       

       

      De: diy_3d_printing_and_fabrication@yahoogroups.com [mailto:diy_3d_printing_and_fabrication@yahoogroups.com] Em nome de Graham Stabler
      Enviada em: quarta-feira, 27 de fevereiro de 2013 9:05
      Para: diy_3d_printing_and_fabrication@yahoogroups.com
      Assunto: Re: [diy_3d_printing_and_fabrication] Servo motors

       

       

      if you do the sums to get say 0.1mm of resolution at the end effector needs much much more than 2048 ppr 

       

      Graham



      On 27 Feb 2013, at 11:32, Murilo Lana <murilo@...> wrote:

       

      Take a look at www.keling.com

       

      They have servos and other stuff at a vey good price.

      About the encoder I recommend the AMT CUI capacitive encoders. They cost about 25 bucks and have selectable resolution from 48 to 2048 PPR quadrature. Much simpler and cheaper than optical encoders. 

      Enviado via iPhone


      Em 27/02/2013, às 07:37, Graham <grezmos@...> escreveu:

       

      I doubt you would achieve suffiecient positioning resolution with that robot, the angle errors add up quickly, you really need extremely hi res encoders and servos, I doubt the installed encoders are up to it nor will the gearbox quality be up to it probably

      Graham

      On 27 Feb 2013, at 02:39, "prkeays" prkeays@...> wrote:

      > Scorbot training robotic manipulator

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