Maxon will occasionally donate motors to students in my experience, but I have not found them to be particularly generous with hobbiests and their motors tend t

Maxon will occasionally donate motors to students in my experience, but I have not found them to be particularly generous with hobbiests and their motors tend to be fairly pricey. You might consider the motor control packages from this guy http://www.kelinginc.net/index.html http://www.kelinginc.net/index.html or similar. They close the loop for you and you position your motor based on a pulse train which can be generated by a variety of devices. The step-direction control of the servo does tend to generate more vibration than other kinds of inputs, but is very easy to interface with. There are others vendors as well, just search for hobby cnc and servo and examples will pop up. Advanced Motion Control also offers servo amplifiers which take other forms of input than step and direction which might be quieter. As mentioned before, gear boxes are a big producer of noise as are powertrains in general. Toothed Belt drives, especially at low speeds or capstan drives for finite rotation machines can be very quiet. To figure out your motor sizing you need to estimate the speeds and forces / torques on your system. From there you can estimate the power your system needs to produce and then calculate a gear-ratio based on the available motor torques and powers available from off the shelf devices. Maxon's catalog has design rules, equations and worked examples if you want samples of the math. For what it is worth, I would guess that the Kelling 350W motors would be able to move a 2KG mass with what looks to be high accelerations and speeds with a decently designed drivetrain.