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Re: binding process ,selection of material and resolution

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  • afogassa
    ... it won t work. Rc servos have a limit travel, if you hack it to turn many times then you need to adapt encoders to it to keep track of position. Rc servos
    Message 1 of 6 , Apr 19, 2009
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      --- In diy_3d_printing_and_fabrication@yahoogroups.com, "infibit" <infibit@...> wrote:
      > Fogassa I worked with many RC servos.One can get a minimum angular resolution of 0.1 degree.Will this help improve the resolution of printing.This servo here:
      > http://www.himodel.com/radios/30Kg-cm_Large_Torque_Metal_Gear_Servo_S8166M.html
      > is a pretty cheap one compared to the torque it offers.It gives you a resolution of 0.075 deg.Also on commercial 3D printers the minimum layer thickness is 0.0035 inches which is about 0.09 mm.Can we achieve this using the servo mechanism?
      > I have worked with servos and they are pretty easy to control.
      > Please let me know.

      it won't work. Rc servos have a limit travel, if you hack it to turn many times then you need to adapt encoders to it to keep track of position.
      Rc servos works by getting a feed back position from a potentiometer
      and converting the voltage to a pwm signal, then it compares the Rx pwm signal from the internal servo potentiometer and adjust position based on the pwm signal ,it's like a analog position feedback
      As a potentiometer can only move 270 degress it's impossible to make a full servo rotation and keep track of position.
      As the feed/build bin moves about 8" up/down you need alot of turns on the lead screw.
      high end servos are digital, I don't know how it works.
      You can achive any resolution you want if you use comercial servo motor and drive.a cheap servo motor+drive runs for about 200 U$D a step motor and drive is about half of that.
      the main difference between servos and steppers is that if you overload a stepper it will lose position, servos won't.
      The cheaper solution is step motors.
      A step motor has 0.9 degress resolution if it's driven in 1/2 step mode.
      Resolution is your lead screw pitch/step drive resolution.
      Let's say you have a sep drive running at 1/2 step and you have a 1.25mm leadscrew pitch. at half step (1/2) the motor takes 400 steps to make a full revolution then 1.25mm leadscrew pitch / 400 = 0.003125
      So each step on the motor = 0.003125mm move on the leadscrew nut, thus if you want 0.09mm resolution you need to tell the step drive to send 0.09/0.003125= 28.8 steps.
      as you can see, the resolution on a step motor is far more then needed.
      Servos are good for high speed needs, like my cnc router :-)
      But I'm using steppers on my laser with speed of 1800"/min. with a resolution of 0.001" per step, this is 10 faster then my cnc router but not strong as.As you can see you can adapt the resolution and speed to whatever machine you make based on transmission resolution.

      Take care.
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