M3HoleDiam = 3.4;

MountSize = 40;

$fn = 100;

difference() {
    MainBody();
    M3MountHoles();
}

module M3MountHoles(){
    edgeDistance = (MountSize-20)/2;

    translate([0, edgeDistance, edgeDistance]) M3Hole(40);
    translate([0, MountSize-edgeDistance, edgeDistance]) M3Hole(40);
    translate([0, edgeDistance, MountSize-edgeDistance]) M3Hole(40);
    translate([0, MountSize-edgeDistance, MountSize-edgeDistance]) M3Hole(40);
}

module M3Hole(thickness) {
    rotate([0, 90, 0])cylinder(h = thickness, d = M3HoleDiam);
}

module MainBody() {
    // left mount plate
    cube([5, MountSize, MountSize]);

    // bottom frame plate
    translate([5, 0,0 ]) cube([50, MountSize, 5]);

    // motorholder plate
    translate([0, MountSize,0 ]) cube([40+5, 5, 40]);
}