$thickness = 3;
$foot_depth = 100;
$flatness = 2.5;
difference()
{
translate([$foot_depth/$flatness,0,0]) cylinder($thickness,d=$foot_depth,$fn=100);
translate([$foot_depth/2+1,0,$thickness/2]) cube([$foot_depth+1,$foot_depth+1,$thickness],center=true);
translate([-($thickness+$foot_depth/2),0,$thickness/2]) cube([$foot_depth,5,$thickness],center=true);    
}