I'm designing a small scale X,Y,Z overhead crane. it is for moving objects to accurate locations in a 2X2X1 meter tank. for the X and Y movement it will have a rail and a on it a cross rail. for the z movement i have to make a lifting mechanism to move an object of around 1.5 kg up and down. for all 3 movements i am going to use a stepper motor because of its accuracy and ability to hold postion. for the lifting mechanism i've thought of a rack and pinion arrangement but it i think it will increase the weight a lot. plz suggest a suitable lifting mechanism. also suggest mechanism for x-y movement (rail and cross rail) using stepper motors.