Is it possible to use an old hard drive to spin ground glass?
 

Hi,
I am completing my 'Agus35', but am already thinking of ways to improve. The first thing would be to replace the plastic cd with real spinning ground glass. I was thinking weather it would be possible to use the internals of an old faulty hard disk drive to attach a spinning ground glass? The internals seem perfect for this use, as its designed to spin several disks that must weigh more then 1 glass disk. It could spin at high rpm and also be very quite. Im guessing the motors in these things are brushless motors meaning much more quite and longer life, and im sure you can use the onboard electronics in order to make the thing spin?

I have read nearly every post on this topic of spinning real ground glass, and it looks like Bob Hart has done the most research on this subject, but did he ever get anywhere with the idea? Bob, if your around I could really do with some help!

Any help would be great,
Wayne.

Wayne,

From a technical point of view, I think that's not a bad idea. The biggest hurdle you'll face is relocating the drive electronics out of the way so that you can have an exposed face on the spinning disk to project through. I would even go so far as to suggest using an older 3.5 inch drive spinning at lower rpm.

Interesting idea though.

-gb-

Thanks for your reply, Greg.

An older model will probably be more suitable, yeah. You can buy these faulty drives off ebay for a few bucks.

Do you know how easy it is to take these things apart and remove the (metal?) disks? Is it all just screwed together?

I found this website about using the internals of hard drives for other applications, including the spinning motor, and how to wire it up using the onboard electric speed controller: http://www.epanorama.net/circuits/diskstepper.html

I hope Bob Hart can help out on this one.

Wayne.

I have had a look at hard drives and agree that the motors are an attractive option for spinning a full sized CR-R disk. The centre of the hard drive I have studied however is a bit wide and it seems that there will only be just enough space on the outer portion of the CR-R to fit the standard 4:3 35mm movie frame of 24mm x 18mm. The motor appears to be the brushless type and requires a control and drive circuit. I have not yet dismounted the motor from the die cast drive case. If there are things like permanent magnets integrated into the case itself, then it will be a dead end. The motors are built for continuous duty and high rpm which should iron out any runout in the disk. The same high rpm may however cause breakage of a thin glass disk due to gyroscopic forces which will be correspondingly high and resistive to pans and tilts. I don't relish the idea of glass shards coming off a disk spinning at 7200rpm remaining within the confines of a CD-R retail case. A piece coming off a disk rotating at 1500rpm was enough to smash a big chip off a prism in my gadjet. Floppy drive motors are not continuous duty motors in the same league and their RPM is very slow and possibly too slow to adequately dissolve the grain of a groundglass at 1/50th of a second shutter speeds. Another motor which might work well would be the drum motor of a VHS video recorder or the mirror motor of a checkout scanner.

These motors should run very true as they appear to have long life ball bearings in them.

I'm way out of my league when it comes to electronics so you would best learn from others on this subject.

I'm not a big follower of the whole mini35 stuff so forgive my ignorance if its been suggested but wouldn't a computer fan motor be fairly acceptable. It has an intergrated controller, is brushless, can be obtained very easily.

A quality delta 60mm fan should be enough to spin a glass big enough, but it might be loud if you want to try running it fast. Should be easy to modify (cut the fins and body away).

They are continous duty and no controller is necessay - just apply voltage, and some even have an rpm feedback line to tell how fast it is spinning. If I remember correctly the vancecam used a fan motor to accurately spin a shutter for a camera that was a hefty piece of plastic.

Keith,
I have also been thinking of a pc fan motor to. I knew some were brushless but didnt know the controllers were intergrated? Ill research into the right away. Thanks for pointing that out to me.

Wayne.

I'm not building a mini 35 clone either at this time, but to answer the concerns about glass shards coming off of a glass spinning at 7200 rpm. That's why I suggested an earlier, slower spinning hard drive in my original post. If you went back to an older 5 1/4 drive, you would also have a motor that was designed to turn a larger diameter disk. Something like an old Seagate ST-225 20mb drive. Whatever you mount in there, it needs to be balanced in some way just like your automobile tires so that it won't vibrate and/or shatter. I was in the semi-conductor industry for 25 yrs and I can tell you that it's not pretty when a 6 in. diameter silicon wafer comes apart at 10,000 rpm from not being centered properly on the vacuum chuck. BTW, that's how the photoresist is applied to the surface in such a thin layer.

Thanks for your help guys,

Greg, i certainly know what you mean by the importance of being balanced. I have been doing radio controlled model helicopters for years, and its the same thing having to have the blades perfectly balance otherwise you get major vibration.

So in that case, if i get a circular glass cutter, how would i go about fixing this glass to the pc fan to get it perfectly central? I think this is the biggest challenge in this design.

Anyone got any clever ideas?

Wayne.

One of my technical reference books says that some DVDs/CDs are mastered on glass. You might try to find either a place that does mastering or the supplier of the blanks and see if you can sweet-talk someone there into sending you a few glass blanks.

Wayne,

Computer fans act just like standard brushed dc motors. IE: Spin faster at 12 volts rather than at 6 volts. So even though they are brushless they are very simple to operate. If you want it to go faster just supply more voltage (until the limit of course).

Sorry that its a little off topic on the Computer fan motors, I know you guys are talking about hard drive motors. On that topic though, brushless DC motors like that have hall sensors that detect position of the drive, so you can make a simple driver for it from a few transistors that activate a coil depending on the state of the hall sensor.

No No!!! I appriciate the idea and help man. Going from my model helicopter days, on a brushless motor the speed was not determand by the voltage as a brushed motor, but by the speed controller. This maybe down to the difference in the speed controllers used in model aircraft.

So your saying that on a brushless pc fan, if you supply less voltage the motor will run slower like a DC brushed motor would? This as great news if this is true.

Anyone have any ideas about centring the glass on the motor to avoid vibration? With a diamond drill bit, 3 holes could be cut into the glass in a triangle shape to hold it to the motor, but how to get them holes central?

I think if we can get this design idea going, it will give us the best 'spinning ground glass' version as far as quality is concerned.

Thanks,
Wayne

Wayne, that is absoultly correct operation of a brushless fan motor. When the hall sensor is tripped by the pole of the magnet and it just turns on a transistor - What ever voltage behind that transistor gets sent directly to the coils, so with more voltage the magnet force increases and results in it spinning faster. Very simple but effective controller.

Also, I think the fan blades make much of the noise so once removed they should be more quite I think.

I'm definetly thinking that the centering wil be the hardest to do, but I don't have a clue about how to make well placed mounting holes.

You could put a circular piece of glass in a metal lathe to find the center, but thats all I can think of

To find the center point on a piece of circular glass, make a square pattern on a piece of paper whose side dimensions are the same as the diameter of the glass. Draw two diagonals inside the square. Where the lines intersect is your center point. Place the paper under the glass making sure both sides are in alignment. Since the glass is clear(unless you have already frosted it), the center point will be visible directly under the glass.


-gb-

Yeah,
The centring will be the hardest thing to get right. Maybe an idea would be to get a 5x6 glass from a photo frame, drill 3 holes using a diamod drill bit in the centre as best we can (maybe using Greg's method above) then mount it the the motor of the fan.

Next, apply low voltage to the motor to start it spinning very slowly, then as its spinning use a perminant marker pen and touch the area of glass with the point of the pen where we want to cut (about 2 inch from centre). This will result in a black line running around the glass in the exact position where it needs to be cut. then cut at the line using a circular glass cutter. This way, the cut should be perfectly central in relation to how its mounted on the motor.

Do you think this would work?

Wayne.

If you were to do it the way I suggested, you could then take a template of the three holes, draw straight lines between them, then draw 90 degree perpendicular lines toward the center from the midpoint of the 3 sides of the triangle. Where the three lines intersect is your center point of the three holes. Align this new centerpoint over the one found in the earlier post. Easiest way to do this is go to the school supply section of your favorite store and buy a 30-60-90 triangle. You could also draw a line from the three hole centerpoints at 30 degree angles toward the center and accomplish the same thing.

-gb-