DIY USB Servo-Guided Water Gun 66
An anonymous reader writes "What better way is there to learn something than by making your own DIY gadget? Here's a new video showing how to use a common hobby servo, in conjunction with a small water pump, to create a USB controlled water gun! You can use your keyboard to aim and fire at an unsuspecting passerby. Both fun and educational, this project looks like a great DIY weekend project for any IT guy, wanting to make sure people think twice before asking a stupid question!"
Re:And if using a hard drive step motor? (Score:2, Interesting)
That's probably the worst brushless dc controller ever built. As you can see in the video the circuit cannot recover from too low rpm of the motor. He mentions better waveforms at the bottom of the site, though.
A proper sensorless BLDC controller measures the back EMF at the undriven coils and uses that information to figure out which coils to drive. Also you don't need a common ground for the coils, instead the polarity should switch when both ends of a single coil have the same potential. Of course it's possible that each of the coils actually has a third contact in the middle.
Properly driving a sensorless bldc motor is quite an interesting challenge for microcontroller programming. You'd need the analogue input and 3 PWM channels. Probably 3 digital outputs, too to switch the polarity.
In other words: I'm taking apart a harddrive right now.