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Old February 12th, 2006, 05:08 PM   #1
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CD-ROM motors

I recently killed a DVD-ROM and a CD-burner (2x, bought for $350 in 1998 - that hurt!). What I found was two very nice motors. They seem much more solid than the ones in portable CD-players and have a very nice way to fit the cd. They use a magnet to squeeze the cd to the motor, making in easy to fit different cd's.

Anyway there's one problem. Both the motors have a circuit board attached underneath, and the problem is that I don't know where to feed the motor with power. I haven't yet tried to remove the cirtcuit board since they also serve as a very good mount that might be useful for mounting the motor in the DOF-adapter. Also, I haven't figured out how the motor actually is attached to the board.

So, what I really wonder is if anyone else has tried to use these kind of motors, and in that case, where was the power fed to the circuit board? Or did you manage to remove the motor from the board? If I find the motors I can post some photos.
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Old February 12th, 2006, 05:22 PM   #2
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Hi,
Early on in the SG35 development I looked at these as well as hard drive motors. Problem is, they are brushless motors and as such, require a brushless controller. This is most likely what this board attached is. I think there are guys around here (Keith Wakeham) that could help with wiring it up?

I ended up using a PC fan motor for the SG35. Its brushless and has an intergrated controller. Problem is finding a high quality fan motor thats up to the job.
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Old February 12th, 2006, 05:47 PM   #3
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I've also, inspired by your work, tried a chassie fan. Unfortunately, it was low quality. I also had major problems centering the cd, which resulted in an oscillating device. Wobbling was also an issue.

I just read some article explaining brushless motors, didn't really know what they were. Know I see the problem.
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Old February 12th, 2006, 06:01 PM   #4
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Carl,
Yes centering the disk was the first major problem, there is a thread about is somewhere i started. Also made it harder that i was using a real glass disk.

Lets just say the trick was mounting the glass then cutting the circle out after its mounted.
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Old February 12th, 2006, 07:39 PM   #5
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Carl, I have a bunch of (new) 3 - 4.5 volt motors including collets to allow mounting a spinning disc with 5mm centre hole. pmail if you're interested.

Got discs too!
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Old February 13th, 2006, 01:29 AM   #6
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Many of those brushless CD-R motors have the same shaft diameter as the DC motors. They are also used in some DVD players and most likely exclusively in DVD recorders. They also have the same end-float issue as the DC motors.

Provided you set backfocus when the motor is running, it is something you can live with as the magnetic field will centre the armature of the motor once it reaches speed.

It becomes a problem if you are moving the camera about violently or tilting up or down. In those crcumstances the motor likely will chatter in end float and spoil the focus.

Best practice is to try to add a thrust bearing. If you can harvest the thrust device from the player, and set it up the same, this is the best solution.

Some forms of these motors you can carefully prise the hub off and remount to a DC motor. With others unfortunately, the motor shaft prefers to remain integrated in the hub and actually pulls out of the motor itself. It reinstalls into the motor no problem.

Pulling pressure to remove the hub has to be applied at the very centre against the motor shaft as the hubs will break otherwise. Some of the hubs with a full metal flange cannot be removed without damaging them. They never run true afterwards.

Bear in mind, these brushless motors emit a high frequency whistle but this dissipates after the motor runs up to selected speed and the loading comes off.

If you use the brushless or the player motors, make sure you use the front mount screws and not the soldered connections or the board at the back, otherwise it may be harder to get the disk to run true bcause of the extra leverage an out of balance state will have on the mount structure.
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Old February 13th, 2006, 11:33 AM   #7
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I realise my hasty grammar may be confusing in the previous post.

Some of the DC motors are mounted by the front screws to a metal panel. They often have a common "L" shaped circuit board attached to them. The motor in and out contacts are soldered directly into the board and are the sole means of supporting the board.

I don't recommend using the board itself as a motor mount. It seems a robust attachment to the motors but it is not intended to be a stressed component.
This is what I was getting at in my post above.

Unsoldering these connections and attaching wires to the little posts on the back of the DC motors is fairly simple. Don't dwell on the posts too long with the soldering iron as the plastic insulation around the posts may soften.

If you don't have a solder sucker for drawing the solder out of the joints, try fine copper braid from around shielded cable as a wick or a wet soft toothbrush swept rapidly in a single stroke across the melted solder.

You will find there is enough flex in the board that you can alternately heat one connector and draw the motor away slightly, then go to the other, then back to the first one and eventually rock the motor away from its soldered joints.

The brushless motors still require their controller circuit and it is not a simple task to use them for an electrical novice like me.
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