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  • teun's instructable Constructing a Robot Arm's weekly stats: 4 weeks ago
    • Constructing a Robot Arm
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      6 comments
  • teun commented on teun's instructable Constructing a Robot Arm1 month ago
    Constructing a Robot Arm

    If both arms would move at the same time in the same direction with the same angular acceleration relative to their own center of rotation, let's say 20deg/s^2, that would result in the end effector moving (relative to the base) at 40deg/s^2. I'm not sure, but can these accelerations be added up without creating difficult second order effects? If so, than the 40deg/s^2 can just be included in the formula for sizing the motor. However, it doesn't happen offten that the maximum load at maximum reach is accellerated by both motor in the same direction. With programming, the motors could be opperated so that when they are at e.g. 80% max reach, and both accelerating the in the same direction, only one motor is allowed to move at at time.

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  • teun commented on teun's instructable Constructing a Robot Arm1 month ago
    Constructing a Robot Arm

    This image should not be completely black... hopefully

    Thanks! I'm happy how the arm optimalisation pattern turned out to be.Good question, it made my think back to when I was figuring out how to calculate the motor torque. I added an image to help with the following explaination,but in this preview window it looks like a black square... we'll see what happens when I hit the reply button.Any position of the end effector, except for when both upper and lower arm are in line with each other, can be reached in two ways of positioning the arm. Either by both arms rotating counterclockwise, or one rotating counter and the other rotating regular clockwise (see image).Often the movement can (and should) be done by rotating the motors opposite to each other. When however this is not possible, the arms are by definition not fully stretched, so the e...see more »Thanks! I'm happy how the arm optimalisation pattern turned out to be.Good question, it made my think back to when I was figuring out how to calculate the motor torque. I added an image to help with the following explaination,but in this preview window it looks like a black square... we'll see what happens when I hit the reply button.Any position of the end effector, except for when both upper and lower arm are in line with each other, can be reached in two ways of positioning the arm. Either by both arms rotating counterclockwise, or one rotating counter and the other rotating regular clockwise (see image).Often the movement can (and should) be done by rotating the motors opposite to each other. When however this is not possible, the arms are by definition not fully stretched, so the effective length of the arm (x force) is reduced in calculating required torque. Adding to this, most torque is required when the load is accelerated, when the effective arm is the smallest. As the arm moves closer to where the effective arm length is the maximum arm length it will decelerate the load, adding negative torque to counter the inertia of the mass.A programmer could program in that when the arms are close to fully stretched out, the acceleration is decreased or that the motors do not move at the same time.In my mind this explaination makes sense, what do you think?.

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