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My goal is to create a cheap and capable robotic arm (Capcharm = CAPable CHeap ARM) using as many recycled parts as possible (mostly from old scanners and printers).
So far, the arm has fully functional shoulder and elbow.
The shoulder uses a DC motor and an axis mounted magnetic encoder for position feedback. The elbow uses a stepper motor. I may be using it above specs as it gets quite hot. I need to add position feedback to the elbow in order to detect missed steps.
Both are controlled through an Arduino. I am getting reasonably good results at controlling the shoulder in position and velocity. The shoulder can follow a trapezoidal velocity profile with little deviation thanks to a PID controller. With open loop position control (generation of a trapezoidal velocity profile, then closed loop velocity control), positioning precision is about 1~2%. I can't wait to add closed loop position control (actually, double loop position+velocity control, as in real industrial robots).
As of now, elbow control is simply servoed to shoulder position. Thus, both joints are proportionally synchronized and shoulder velocity profile is scaled down if necessary, so that the elbow doesn't exceed its maximum velocity.
When I'm done with closed loop joint motion, I'll see what I can do for Cartesian motion. :)