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I've seen CS's Doom3 mod, first of all, the man is a legend, all we need is a mini Marine and some ghosts swarming around the case!!
So, I came out with one question, what makes a CD tray motor change its mind and go backwards and forwards??
I'm sorry if anyone is bugged by all these questions, but I feel if I understand "how stuff works" then I can get a better design.
Passing the electricity through it in the opposite direction makes it turn the other way. Not all motors can do this, but obviously the motor in your CD drive can.
-Dave
Yes I know that, I was wondering if there was anything inside the motor itself that changed the direction of the current?? You see, I saw the videos in CS's Doom3 mod, and saw the CD motors change directions, may be he used a switch or something. But how does it happen in a normal optical drive??
The easy way to drive a DC motor in two directions is with an H bridge.
Turn on the transistors in diagonally opposed pairs.
So, top right + bottom left, current passes right to left.
So, top left + bottom right, current passes left to right.
Turn them all on and it blows up...
Doh!! Sounds like experience talking there!!! :)Quote:
Originally Posted by xmastree
Sort of. I used to work with such circuits, but driving big stepper motors. Big, as in about 6" diameter and 12" long, running of a 60V supply. If the logic failed, then the wrong combination of transistors would turn on and let the smoke out.
You might want to also look at Mashie's Y2K bug mod. He's using model boat sail servos to open and close the wings of the bug on startup.
I'm currently doing a mod that has a door similar to the Doom 3 mod. I'm using a servo modded to be continuous with a servo tester attached to control the movement from a knob. http://www.robotlogic.com/product_servotester.html
I'll let you know what I find out as things progress.
xmastree is correct that you can burn up the motor if the motor is not stopped before reversing direction or something similar. Most sites that I've found recommend a series of relays to control the motors. I experimented with the phidgets servo kit for the control and will be using their USB knobs for other interfaces but the servo tester above was a more compact solution.
IIRC, the Doom 3 mod doesn't use microswitches. The motor opens with the switch and closes with another. In the off position, the door is stationary. This is the blast door btw.
It's not the motor which burns. If you imagine all those transistors on at the same time (or any two on one side) there's basically a dead short between the suply rails. The fuse ought to blow, if there is one. If it's a fast enough one, it will blow before the transistors...Quote:
Originally Posted by Mach
I'm electrically challenged, I must admit I understand fragments of what you say! To get started, what does a transistor do and how does it work?? And what makes 2 transistors work alternately?? Sorry if you're getting bored or anything.
Think of them as switches.
Apply a small signal to the base (the middle connection) and it allows much higher current to flow between the other two.
Actually, they're more like throttle controls. If you know about engines this will mean more to you. However, in this application they should be either fully on (throttle open) or off (throttle closed). Nothing in between.
As for making them work alternately, that depends on the control circuitry.
The bases are the ones without conenctions on my drawing. To turn on the bottom ones, you need to push current into the base, by connecting it to a positive voltage with a resistor to control the current.
For the upper ones you need to pull current out of the base, by connecting it to a negative voltage via a resistor.
You could, in fact, connect them together with the resistor, so that each one becomes the other's source.
