Add design files for hardware

implementation/SCARA/hardware/hardware_specs.md

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+# Specifications requirements for MCU
+For my whiteboard writer I require a microcontroller board that will be responisble for the control of the system.
+For the operation it has to drive four stepper motors and one servo.
+For the homing of the stepper motors some analog sensors are planned.
+The system requirements are divided in to four categories:
+
+## Must
+
+1. Connect to four stepper controllers ([TMC2208](https://nl.farnell.com/trinamic/tmc2208-silentstepstick/stepper-driver-board-2-phase-motor/dp/2822166)) via UART.
+2. Have debugging capabilities.
+3. Read read four analog sensor signals.
+
+## Should
+
+1. Connect to each of the four stepper controllers directly. Prefered over a switching solution.
+2. RIOT-OS support.
+3. have UART-baud > 200k
+
+## Could
+
+1. have a FPU.
+
+## Wont
+
+1. force me to work with MBED.
+2. run on dieselfuel.

implementation/SCARA/hardware/openSCAD/arm1.scad

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+
+$fn = $preview? 32 : 72;
+
+// arm 1
+rotate([0,0,90]) arm1();
+
+// arm 2
+thinkness=3;
+width = 10;
+bore = 4;
+rotate([0,0,180]) {
+translate([0,0,thinkness])  arm2();
+translate([0,0,-thinkness]) arm2();
+}
+
+// arm 3
+translate([-25,0,0]) rotate([0,0,90]) arm3();
+
+// arm 4
+translate([0,65,thinkness]) arm4();
+translate([0,65,-thinkness]) arm4();
+
+module arm(holes, width, thinkness, bore){
+    difference(){
+        hull(){
+            cylinder(h=thinkness, d=width,center=true);
+            for(hole = holes){
+                translate([hole,0,0]) cylinder(h=thinkness, d=width,center=true);
+            }
+        }
+        for(hole = holes){
+          translate([hole,0,0]) cylinder(h=thinkness*2, d=bore,center=true);
+        }
+    }
+}
+
+module arm1(){
+  arm([0,65],width=10, thinkness=3, bore=4);
+}
+
+module arm2(){
+arm([0,25],width, thinkness, bore);
+}
+
+module arm3(){
+arm([0,65],width=10, thinkness=3, bore=4);
+}
+
+module arm4(){
+arm([-25,0,50], width, thinkness, bore);
+}

implementation/SCARA/hardware/openSCAD/arms.scad

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+use  <arm1.scad>
+
+arm1();
+translate([0,15,0]) arm3();
+translate([0,30,0]) arm2();
+translate([40,30,0]) arm2();
+translate([25,45,0]) arm4();
+translate([25,60,0]) arm4();
+