The assignment specifications translated into a pretty simple solution in the hardware simulator.

I also provided a Java solution to show how it would be implemented in software. But an actual hardware solution is invaluable in seeing how everything fits together.

This cracked-open drive, which I've used for years for show-and-tell, was a perfect candidate. It's still in good shape, although it obviously doesn't work anymore.

Here are some of my other demonstration goodies. Eye candy gets kids' attention.

I used to have a ton of these drives, but I gutted them for the platters, which are great for machining.

The guts are easy to disassemble without damage. Of course, this thing doesn't work anyway, but I want it to look as though it still did.

Here's a test of using a servo to drive the arm. The original voice coil is still operational, but it's a nasty animal to drive. I don't want to go there. This is supposed to be a quick, relaxing project over a few evenings.

Likewise, driving the original platter motor isn't an option. I want complete control over positioning at any speed, so I'm using a stepper motor. But first, I have to get the seal off the original motor to see what's in there. I took a few stabs at it (see the dimples) with no luck. Now it's time for real action.

A quick stab with a 1/2" end mill did the trick!.

The servo and the stepper motor will be located below the hard drive so the top looks original. Here the channel for a vertical connector from the servo horn is being cut out. This was done by hand because it's not a precision job. I'm trying to do this quickly, and this hole is covered anyway.

The same goes for the circuit board. I think this voids the warranty...

Now it's time to dig through the box of motors for something suitable to drive the platters.

The disk drive already has its own embedded motor, which I needed to circumvent. This involved boring out the original shaft to make room for the shaft on my stepper motor. It was actually a three-step process with progressively bigger cutting bits. This is the smallest.