CD ROM Read Head Actuator - Hacked Gadgets

http://hackedgadgets.com/2009/04/29/cd-rom-read-head-actuator-head-scratcher/

Here is the question. The CD-ROM drive had 3 DC motors, one to open the drive door, one to spin the CD and one to move the read head back and forth. We normally see a small stepper or something similar that can provide accurate position moves of the read assembly. In this case the read assembly moves via a rack and pinion drive system powered directly from a DC motor. When there is a CD in the system I can imagine that the drive would be able to get accurate head position information by reading the CD tracks but how could it move with any accuracy? It has me puzzled, if anyone can fill in the blanks I would be real interested to find out what makes this tick.

Category:

Science & Technology

Tags:

• CD
• ROM
• Read
• Head
• Actuator
• Hacked
• Gadgets

[fizxgod]

how many leads are coming off the motor area? if more than 2, there's probably an encoder.

if just 2 wires, it's probably just a simple open loop control system. (i.e. on/go-off/stop)

[abbtech]

You can see the pictures here. There is just two wires on the motor. I am wondering if it is looking at the CD information for position and shorting the motor windings when it is in position to quickly stop the travel.

[Davidbzm01]

dude. thats not a hack. thats just a ripped apart cd rom. WTF

[physicmad]

When the laser is scaning you have two levels of track allignment - major and minor, the major track alignment is performed by the motor moving the head assembly. Now to keep the laser acurately set on the pit track, the lens head iself has an 2d plane movement. if you were to look at the lens focus coils, they are indipendently wired. If both are powered with the same voltage the head goes up and down. if one coil is powered and the other has the opposite polarity it moves side to side.

[zolberserk]

do you know what the 17 pin connector RFO VR PD LD C B A E F VCC VC GND FCS TRK TRK+ FCS+

[idricool]

You morons the group and website is called hacked gadgets. Fucking retards. No one claimed the Cd rom "was hacked".

[canadiandude1919]

whats the model??

[flash11588]

yo some one would me the man if he can get a dvd laser the work in the dreamcast

[nrdesign1991]

There is a tiny push-switch that the head triggers when fully moved in (to the spindle motor). The position of the head is controlled by timing the power that goes to the motor. The actions the motor can do is stop (short wires), forwards (normal polarity) and backwards (reversed polarity). If the head loses track, the motor simply drives it back into the reset positikon. You can easily confuse a CD drive by pushing the button :-)

This assembly is cheaper to make, that's why it took over.

[ZXRulezzz]

DC motor that moves head assembly, and some circuitry that controls that motor, actually acts together as a servo.

Control circuit are designed to control not a movement, but motor's angle depending on a data that comes from the laser head itself.

[Gonamez]

???

[physicmad]

if you listen to a portable CD player, you can hear the motor pulse as it passes each block,

[physicmad]

now this side to side lense movement is what gives the minor track allignment. Since the motor has a absolute minimum movement the motor is only used ot move the laser lens to the next "block" or so. the lens control "stitches" these blocks together. making the data read seamless.