dvd rom motors, servos, steppers

anyone had any experience of using these parts? i have googled and had zero luck on finding info on these.

Thanks Haydn

You mention three different things...

There is lots of information in the playground about stepper motors.

"servo" motor is a bit ambiguous. It can mean a radio control "servo", which usually includes motor, geartrain, and assorted electronics, designed to move a shaft to a particular position based on a digital input. It can also mean a random high-performance motor usually designed for use with position feedback systems (ie the motors in half-inch computer tape drives were frequently known as servo motors.) There is lots of info in the playground and forums on the first type of servo motor.

Now. DVD ROM motors. The average DVD drive yields three motors. There is usually a DC motor for moving the tray. There is a DC or stepper motor for moving the optical head. And there is usually a three-phase spindle motor for spinning the disk. It's the last one that people are usually interested in, since they tend to be pretty powerful, and ... unusual. There is a lot of information on using such spindle motors, either as-is or "modified" in the RC plane community, but they tend to rely on commercial speed controllers (or dedicate entire arduino-class electronics to just running the motor.) This isn't out of the question; you can get such speed controllers for less than $15, and you control them pretty much like RC servos.) In THEORY, you can also drive them like stepper motors with one-too-many or one-too-few coils, and I've always thought that there ought to be a pretty simple circuit that would let a microcontroller drive them in a rather slow and jerky fashion, but I don't think I've even seen one :-( (Another problems is that such motors tend to be pretty power-hungry, even if you're just trying to make them hold a position...)

DVD-ROM and CD-ROM motors usually also contain three hall-effect sensors, which are used by the motor controller to sense the angular position of the rotor. Then, they do electronic commutation based on the position data. You can use the sensors to make a "spinner" control, rather like the Griffin Powermate.

You can use the sensors to make a "spinner" control, rather like the Griffin Powermate.

Huh. Now why didn't I even think of using just the sensors to implement that sort of thing? I always thought/assumed that people doing that were reading induced voltages from the coils!

You can use the voltages induced in the windings, of course, but the voltages get smaller the slower you turn the spinner! The hall-effect sensors work right down to a standstill. I used three sections of a TLC3704 comparator chip to get three digital outputs from a CD-ROM motor’s sensors:

Imgur

I used three sections of a TLC3704 comparator chip to get three digital outputs from a CD-ROM motor's sensors:

That is so cool... Anachrocomputer, seriously, you're my hero!

:)

Dude, thanks, but wait until I've got a proper description of how to build it, and working sketch code!

I saw this on the makezine site the other day:

http://profmason.com/?p=703