USB powered Centrifuge for under 10$. I used a small DC motor (1.5-6 Volt, 4000 RPM) and a DC motor speed controller kit to make this USB powered Bio-Centrifuge. The Radius is 40 mm (you can make longer rotor arms) and the motor will spin up to 4000 RPM on 4.5 volt/100 mA USB port power giving a centrifugal force of 500 gravities (link to nomogram and online calculator provided). I used 0.2 ml PCR tubes that when filled weigh-in at about 0.5 gram so at 500 Gravities, each "bucket" will weigh about as much as a half of a 17 ounce bottle of water. The capacitor across the terminals of the small DC motor provides enough energy to keep the motor running smoothly when the armature shoots by the stator and to minimize noise in the circuit (you can look that up for a better explanation than I can give). Do you see the small piece of reflective tape on the top side of the Right Rotor arm. That's used by the Tachometer to measure the RPM. It tacked out well over 4k RPM (wicked fast). I used an old USB cable's red and black wire to power it up (with safety gear) and it worked perfectly. Total control over speed. If placed in an appropriate enclosure (like a metal coffee mug) you've got a cytocentrifuge that actually works and uses only USB power, for under 10 dollars. Inspired by: http://www.thingiverse.com/thing:33818 http://www.thingiverse.com/thing:1483 http://www.thingiverse.com/thing:12390UPDATED with "Enclosure Files" for safety 3/4/13. Print out 4 of the "Enclosure" walls and 4 supports. Centrifuge Instructions: Print out the parts. Find an old DC motor from a previous project. Wear safety garb and "spin-r-up" Parts list: 7.99$ FK804 DC Speed Control PWM from Bakatronics Kit makes a 0-12 volt output DC Pulse width motor controller. 20 Watt. Great for hand held switching throttles Detail: • This DC Motor speed control circuit uses pulse width modulation to control the speed of the motor • The potentiometer controls the width of the pulses to control the speed of the motor or train engine. The Pot can be mounted remotely on a control panel of in a FB enclosure to make a hand held throttle. • Power supply : 12V. (can also be used with voltages as low as 5 VDC) • Recommended housing : FB03 • PCB dimensions : 1.8” X 1.3” Add an optional DPDT slide switch for reversing the direction of the motor. 3.00$ DC motor, Find a small DC motor that has speed up to 4k-5k at 1.5-6 Volts. http://www.allelectronics.com/make-a-store/category/400/Motors/1.html 1 Old USB cables from your abandoned tech box. Test equipment that I used: