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.

Sorry that its a little off topic on the Computer fan motors, I know you guys are talking about hard drive motors.

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.

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-

Or just do it in photoshop accuratly and print it out the right size.

Only problem is your only centring the outer diameter cut in relation to the holes in the centre of the disk. even with this perfect, there still maybe offset once mounted to the fan motor.

With my method, it marks the outer diameter perectly taking into account any inaccuracies made when drilling and any slight offset in relation to the centre of the fan motor. Challenge is to cut exactly on this line with the circular glass cutter. I guess both methods are open to potential inaccuracies during cutting/drilling, the question is which method is the most accurate? I guess the proof is in the puddling.

Im just wondering how much better real glass is going to be compared to the plastic CD in terms of light loss?

Wayne.

Or just do it in photoshop accuratly and print it out the right size.

Only problem is your only centring the outer diameter cut in relation to the holes in the centre of the disk. even with this perfect, there still maybe offset once mounted to the fan motor.

With my method, it marks the outer diameter perectly taking into account any inaccuracies made when drilling and any slight offset in relation to the centre of the fan motor. Challenge is to cut exactly on this line with the circular glass cutter. I guess both methods are open to potential inaccuracies during cutting/drilling, the question is which method is the most accurate? I guess the proof is in the puddling.

Im just wondering how much better real glass is going to be compared to the plastic CD in terms of light loss?

Wayne.

I think the glass would maintain better optical properties than the plastic. Maybe not so much with light loss, but maintaining image clarity on the frosted surface. I am purely speculating here.

Totally agree that both methods should work in theory about centering the holes and that the end result depends alot on accuracy of machining. I was putting forward a method that should keep everything in close to perfect relation to the physical center of the glass. That may not get you perfect balance, but it's a good starting point.

-gb-

Greg,
You methed is very good and I think I will be trying both methods in the future. As you point out, getting it spinning without vibration is difficult without special tools, but i think its possible.

The cool thing about my method of using the pen to mark the outer diameter when its spinning, is that the mark will be perfectly central in relation to the axis of the motor, which is whats important.

Wayne.

can you spin it and then mount it against sandpaper so it spins against the sandpaper until it's a perfect circle centered on the axis?

Ben,
I thought of that but think it would take too long. However, I was planning on using my method first to cut it, then do as you sujested to clean it up after. Thanks for your sujestion.

Wayne.

After speaking to Nick Bartleet on this design, he had tried it and failed. His main issues were balance of the glass and gyroscopic effect.

His glass was cut buy a company called Knight Optical. Nick had his glass crack twice. Due to the weight of the glass, the gyro effect has much more force.

So what do you guys think about this issue? Would thickness of the glass help? Would 1.5mm or 2mm be better thickness? 1.5mm would mean lighter but weaker, 2mm would mean heavier but stronger.

What do you all think?

Wayne.

Wayne.

Any of the .jpg files titled "ohara008.jpg" or similar at ww.dvinfo.net/media/hart are tests of a glass disk dressed to 5 micron and slightly backpolished for better light transmission at expense of the "filmlook"

The disks can be had in 1.2mm thickness from ohara in Japan but the downside is you have to dress and polish them both sides then groundglass one side yourself. It is a seriously difficult task and of the ten disks I got in, only two now survive. Four were lost in wax composite disk attempts, one (the best) was broken accidentally in service. Three are still in semi-complete state. If I go glass again, I will likely use the smaller CD-R size and spin them at 3000rpm than the 1500rpm I use with the full size CD-R glass disk. As AU$50 an item, the glass is not cheap to be breaking. I was pleased with the result I got before disaster struck.

Subjectively, I think the image looks slightly more solid than the plastic CD-R spacer result. I've since tried splitting DVD+Rs and I got a good result however they are also difficult to dress as the plastic seems to have some hardening enhancements which resist the grit and take longer to dress in my machine than the actual glass ones. The DVD+R when split is very thin and forgives misalignment if you spin it at 3000rpm (3vdc on a Mabuchi style CD spindle motor.) as it flexes enough to run true on the focal plane. When drewssing, you have to protect the clear surface with stick-on material you can peel off later. I found plastic book covering sheet to be adequate.

Due to some family issues the whole R&D is been on hold for about three months.

Wayne.

Furthur to above, "grabmon.jpg" on www.dvinfo.net/media/hart is an assembly of images shot in a low budget production environment, time pressures, a location, two man crew and powersaver flouro incandescent lamps of combined tungsten 340watts equivalent plus an overhead 18watt overhead flouro light. Lenses were Nikon f1.8 50mm and Nikon f1.8 85mm. Image path was Nikon Lens >> oharadisk >> 2 x 90 degree prism to erect image >> Century Optics 7+ achromatic dioptre >> PD150 P camcorder.

glass disk dressed to 5 micron and slightly backpolished for better light transmission at expense of the "filmlook"

Bob,
Thanks very much for your reply. When you say at the expensive of the "filmlook", do you mean that backpolishing reduces overall diffussion and therefore letting more aerial image through and killing DOF?

The shots of your tests with the disk are very clean indeed. I think i'll try cutting my own glass, dont want to go to the trouble and expensive of getting hold of them disks from japan.

Was gyroscopic effect ever a problem for you?

Thanks,
Wayne.

Maybe the glass can be held on the outside so it doesn't have to be drilled or anything like that. Could build a gear on the outside of a short cylinder and let it rest on some gears that have ball bearings in them.

I've seen a p & s mount for an xl1 and that is how I think they might hold the glass and deal with the weight, but they spin it in the center so you have a spot in the center that doesn't move.

Keith,
Yes thats the design Nick Bartleet went with, but as you point out it spins slower towards the middle and in theory not at all in dead centre. Thats why i didn't want to go down that path.

Wayne.

You can still spin it off center, it just needs to be a larger ground glass, that way the groundglass looks like it is just a continous sheet moving up or down. The P & S I saw spun with the center of the spinning ground glass in the center of the screen, but using a larger gg the center would be off to the side.

You probably thought of that anyway and one side will still not spin as fast as the other but at least you don't see that its spinning in place.

Keith,
That would certainly make the centring of the glass a simple process. Nick Bartleet used a big bearing with a 50mm diameter hole with the ground glass fixed to the inner race.

Is this how you mean? Or do you mean the glass supported by a few smaller bearings? Could you elaborate?

Wayne.

I was thinking something maybe a little larger. Like I said a little earlier, just throwing out ideas, not to experienced with this and haven't followed all so I'm just thinking out loud a lot.

I was thinking a large metal gear with the ground glass placed in the center, possibly 10 - 12 cm in diameter, surrounded by a metal ring with gear teeth that rests surrounded by 3 smaller gears that mesh with the large one which holds the glass and one of the smaller gears is driven by a motor. The other two gears are only to hold it in place. The side of the ground glass would be used to reduce the spinning that you see.

This might not be the greatest setup for simplicity, I'm a little tainted by access to metal lathes and mills and cnc machines. So it might be better to replace the gears with a metal ring that rests on some wheels, with a rubber wheel for grip on the motor.

Again, just thinking out loud. I'm involved with designing some other stuff, but if I get the time I'll see if I can do up a simple drawing or something if needed

Keith,
Your idea certainly solves 3 of the problems of the other designs. I would just be concerned about the ammount of noise gears would make. Probably something you could develope?

Wayne.

I know I can do it and I have the tools, just really busy with another project, but If I have the time I'll do up a little design in solidworks and post a drawing and stuff like that. The gears can be replaced by wheels or small bearings of some kind with a track so long as their is some good grip between the motor and the ring that holds the glass.

I would love to see a design Keith, when you have the time.

Thanks for your input,
Wayne.

Wayne,

i am seeing the problems associated with a plastic GG CD now , the colour separation I wasn't noticing until lately. I am down with the Glass GG if you figure it out for a CD player motor. Keep me posted, pls.

Mandy,
Im still trying to get my agus box together and complete with a support. As soon as I do Ill start work on the real glass design.

If im successful ill post full details and photo's of how I accomplished it.

Wayne.

Keith,
You said that you just apply voltage to a brushless pc fan motor, right? Well, the one I have has 3 wires running from it, yellow, red and black. Do i just connect to the red and black, is the yellow one an RPM feedback wire?

Thanks
Wayne.

Wayne, your 100% correct.

Black is gnd, red is V+ (usually +12v for normal operation) and the yellow is a feedback so it can be ignored. This is the normal setup for almost every fan that I've seen

Thanks Keith,

You have been very helpful

I was wondering. The fan on my CPU right now has a speed control connected to a rotary knob that mounts to the back of the pc. I was wondering if its a good idea to buy a fan like this to controll the speed of the ground glass, as the real mini35 does?

What ya think?

Wayne.

That control knob is called a rheostat (spelling???) and is kind of like a big variable resistor. You should be able to use it without problem to control the speed of the GG so what you want to do should work without a problem.

The only think i'm not sure about is how many watts they can usually dissapate because when that GG first starts spinning the current is going to be high until it gets upto speed, so It is possible to blow the rheostat or even the coils if that initial current is just to much for the fan.

I've never tried spinning glass so the angular moment might just be to much to handle so a really "beefy" fan and rheostat is perferable.

Should probably start the motor on a very low setting with the rheostat because it will keep the voltage low and as a result lower the current so it is easier on the coils and rheo until it gets the GG spinning and then speed it up after.

Thanks again Keith!!!

On another note, what batteries would you recommend for running this fan motor? I wonder if duration will be a problem?

Wayne.

I'd probaly say its all about convience in the battery selection.

The big option I see are AA nimh high capacity batteries like people mainly use in digital still cameras. They are usually around 1.2v @ 2000mah. So if you wanted the fan rated 12v @ .4 amps you need 10 AA's and they should run continously for 4 hours at top speed.

Another option is a camcorder battery. Usually 7.2 or 8.4 volts which is plenty to spin the motor and they are usually pretty high capacity li-ions. The only problem is getting the battery mount, an old charger could be modified for the mount but beyond that will be hard to get a mount for any type of camera specific battery.

Lots of options out their but this are the easiest I think, could be wrong though

Keith,
I think sticking to the AA's NiMH batts would be best. I probably wouldn't need to supply the full 12v, so maybe 6 to 8 AA's would be fine?

The camcorder battery is a good idea, im just thinking about weight. I'll have to compare a heavy duty cam batt and the AA batteries.

Cheers,
Wayne.

2. Glass GG and rotation.

I would not recommend rotating a CD-R sized glass gg at any more than 3000rpm. 1500rpm I found to be adequate for 1/50th second on the PD150.

3. Rainbows in image.

I suspect the culprit to be the close-up lens on front of the camcorder or any home brew condenser setups, rather than the gg. Before going to the ordeal of making a glass spinning gg, try a fixed gg made from a microscope slide first. These are also handy for wax tests.

Does the colour separation occur as a parallel rainbow effect or as a radial rainbow effect - possibly also associated with radial smearing or blur most noticeable at the outer edges or corners of the image. If the separation is radial and especially if the blur is there, then the relay path, ie., close-up lens and or condenser arrangement is likely to be implicated.

A plastic gg which is opaque through its entire thickness is going to confer a halo effect around highlights or sharp light/dark edges, but we are not going to use these for serious imaging are we??

I know my colour separation is not the close up lens, because I was not using it and still saw the colour separation. I am not sure that a glass GG would fix it, but I can't figure out why I am getting it with a plastic GG. I get it when looking at a lamp shade so I can see the inside and the outside (a lower angle). This is combated with closing the iris on my camera, but it makes everything much darker.

Wayne,

8 cells would give you 9.6 volts which should be plenty. These run fine at 7v (people use the 5v to the gnd and the 12v to the power and the potential difference is 7v) So you won't have a problem even with 6 cells because that is 7.2 volts.

Would a 7.2v, 2 cell lithium polymer battery do the trick? as these come in very high capacity.

Wayne

Wayne, lithium polymer would definetly work and great if you can find them, downside is they will require a charging circuit but if you can get by that then more power to you (a pun was so intended)

Hehe, thanks Keith,
Luckily im very familiar with LiPo's from my R/C helicopter days. They are both lightweight and high capacity, but need the special charger.

Something to concider i guess.
Wayne.

To Frank Ladner,

Frank, I read that you are also trying to build a spinning glass solution, using the case from a hard drive? Looks like me and you are the only 2 on this board trying to push this solution. I love the hard drive case idea, im thinking of using that.

Maybe we can get our heads together to come up with a working solution? Maybe we can chat via msn messenger if you wish? my msn is waynekinney@hotmail.com

Looks like the main problem is being able to drill a centre hole in the glass in the EXACT centre. Im very interested to see how far you have got with this.

If you can contact me via email or msn, or even on this thread, that would be great.

Thanks,
Wayne.

OK,
I am just getting ready to buy the tools required to build this spinning glass adapter. Below is what I intend to use:

1:A plastic project box to house everything in. size - MB5 145 x 95 x 57·5 (mm):
http://www.maplin.co.uk/Module.aspx?ModuleNo=1676&TabID=1&WorldID=&doy=3m9

2:1 Circular glass cutter like here:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=4402699540&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1

3:Pack of 1mm Diamond drill bits like here:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=5997131218&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1

4:Coolermaster 80mm Tri-Blade Silent Fan:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=6797075948&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1


Firstly ill cut the fan blades off and the outer body. Ill then drill 3 holes in the centre of a 5x6" glass from a photoframe using the 1mm diamond drill bit, the 3 holes will form a triangle shape to mount to the pc fan.

i will then place the glass in top of the pc fan where it should be mounted as accuratly as I can, then mark 3 holes on the fan. Ill then drill the holes on the fan ready to take 1mm screws to hole the glass to the fan. Ill use rubber grommets/washers, as to prent the screws from cracking the glass when they are tightened.

With the glass mounted, Ill start the glass spinning slowly, then using a perminant marker pen, touch the surface of the glass exactly 45mm from centre (90mm diameter glass), keeping the pen very steady. This will result in a line in the perfect position in relation to the axis of the motor.

Unmount the glass from the fan, then using the circular glass cutter, cut the 90mm diameter glass disk exactly on the line.

Once cut, you can then grind the glass with aluminium oxide (maybe its best to grind before hand?)

Remount the glass and you have it. The glass should be centred perfectly in relation to the centre axis of the motor.


There are 2 possible problems with this method. 1: Any inaccuracy when trying to cut on the line with the cicular glass cutter and 2:making sure the glass mounts to the fan in the EXACT same position each time.

Anyway, im going to buy the tools next week and give this a go. the 90mm diameter disk is the smallest possible while being able to use a 36x24mm frame area. The smaller the diameter of the glass, the less gyro effect i beleive. Ill let you all know how I get on.

Thanks
Wayne.