hi, I'm doing an experiment, in realisation of which i need to move a steel plate up and down. Please consider the following constraints faced by me: -The plate would rise to 12mm at most. -The speed should be such that it rises 12mm in around half a second. -I want to be able to stop the plate anywhere between 0-12mm. -Variation of the speed may also be needed. -The plate will be exposed to high pressurefield above, so will tend to come down. -I have only 75mm(L)*175mm(W)*25mm(H) space to accommodate the lifting mechanism. -I can also mount the motor outside the above mentioned cavity, but the motor diameter less than 30mm is preferred. After considering all the above mentioned constraints, i've thought of getting a miniature rack and pinion system manufactured. But the driving motor is still not finalized and i'm facing a problem in it. Initially i thought of using a geared dc motor but then i won't be able to stop it at the precise positions (4mm say). Servos can definitely be used but the speed control is a problem. Stepper motor seems a good choice but i haven't got much experience working with them. So, please help me choose a good motor or a new mechanism. Thank you in anticipation. Abhishek.