$fn=48;
difference(){
    //full chassis base
cube([16.5,8.2,0.2]);
    // 4 holes for the clamps
translate([6,8,0]){
   cube ([1.2,0.2,0.2]) ;
}
translate([6,6.15 ,0]){
   cube ([1.2,0.2,0.2]) ;
}
translate([6,0 ,0]){
   cube ([1.2,0.2,0.2]) ;
}
translate([6,1.85 ,0]){
   cube ([1.2,0.2,0.2]) ;
}
// the switch
  translate([5,3.5 ,0]){
   cube ([1.3,0.8,0.2]) ;
}
  translate([4.93,3.7 ,0]){
   cube ([0.07,0.4,0.2]) ;
}
  translate([6.3,3.7 ,0]){
   cube ([0.07,0.4,0.2]) ;
}
//the battery holder for imagination purpose
 translate([7.4,1,0.2]){
   cube ([5.8,6.2,0.2]) ;
 }
 //the 2 holes for screws of the battery holder
  translate([10.2,1,0]){
   cube([0.3,1,0.2]);
 }

    translate([10.2,6.2,0]){
   cube([0.3,1,0.2]);
 }
 // the 4 holes of the castor wheel
translate([13.6,2.5,0]){
cylinder(r=0.2,h=0.2);
}
translate([13.6,5.3,0]){
cylinder(r=0.2,h=0.2);
}
translate([15.5,5.3,0]){
cylinder(r=0.2,h=0.2);
}
translate([15.5,2.5,0]){
cylinder(r=0.2,h=0.2);
}
}

// check all dimensions
//make wheel
//make castor wheel
//https://www.thingiverse.com/thing:1755397