Mechanical drive source?

I figured I could use floppy arms for precision positioning. By useing the same mechanical drive as the one positioning the magnetic head in a floppy:
http://www.ohs.rcs.k12.tn.us/Technology/Floppy%20Drive.jpg (178kB)
--------- | Motor | ==============[Head]===== --------- ^ | This "screw"
So where does one get/buy "screws" like this ..? Preferebly slightly longer. like 200mm ;)
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snipped-for-privacy@spamnuke.ludd.luthdelete.se.invalid wrote:

Dunno...I have used a piece of threaded rod and a stepper motor for positioning
Same idea
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I have thought of that too. But I guess speed will suffer. Maybe it also is more prone to jameing ..?
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Hi,
Have a look at old inkjet printers. I salvaged a 30cm long thread (it actually has 6 threads that run parallel to each other) from a old cannon BJ.
Regards Ian Dobson
Home of the Atmel based UDP mobile web cam http://www.planet-ian.com All mails scanned with av-filter.pl (F-Prot / perl)

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Could you post any picture ..? (curious)
Any other parts you found useful?
I looked inside a still working hp5550-usb, it uses tractordrive with some plasticfilm/opto feedback loop to control sideways motion.
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Hi,
I'll post some pictures tomorrow.
I'm also building an XYZ cnc system (pop over to my site and have a look under the projects page). I'm currently using M8 threads to drive the axis (I plan to replace them one day when I have the money). Laser printers are the best for getting good stepper motors, their usually much stronger than the ones used is ink jets.
Tomorrow is the "big wedding" were the controller/X axis, Y&Z axis come together. Uptil now I've only been testing individual parts.
Regards Ian Dobson
Home of the Atmel based UDP mobile web cam http://www.planet-ian.com All mails scanned with av-filter.pl (F-Prot / perl)
wrote:

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You want a lead screw or a ball screw. Do a search on mcmaster-carr (http://www.mcmaster.com/) or SDP-SI (http://www.sdp-si.com /). Lead screws are cheaper, but have only about 30% efficiency. Ball screws are more expensive, but have in general a 80% efficiency. Look on ebay and surplus stores as you will find it even cheaper, but your specs must be flexible enough.
Cheers
Padu
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What do you mean with efficiency in this context? I need precision (~10 mil). But speed or powerwaste is no big deal. My plan is something like 200x200 millimeter X-Y-Z board.

I think I will look into old printers.. They tend to be a good source for stepper motors these days when floppys are onto the scrapheap.
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It is the force utilized on anything other than driving your load. For example, if your motor produces 10Nm or torque, approx. only 3Nm will be transfered to your load if you use a 30% efficient device, all the other 7Nm is wasted on friction basically.

That I can think, there are two things about what you are trying to do. When you say precision, you may be referring to two different things: repitability and accuracy. Accuracy would be the resolution you can move your load. That will depend on the motor torque, speed and backlash on your power transfer system. Repitability is how often can "hit" the same spot. For example, you want to move your load to position 10 and you hit 10 on the target 90% of time, but 10.1 10% of time. Usually it is represented by some kind of statistical distribution. It will also depend on a couple of different things, including what type of sensor you are using for position feedback.

I have automated agents for stepper motors on ebay, they are veery cheap, but printers could be a potential source too. I've never played with them, I don't know how easy it is to hack them, but I know that stepper motors have a pretty standard interface.
One final note though is from my very limited experience, price of things increase exponentially proportional to the degree of precision you seek. In my project, I've tried to define what is minimally acceptable and then go shop for it.
Cheers and good luck
Padu
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[snip]

[snip]
Another source of stepper motors is FAX machines. Thrift stores around me are packed with them, and the last few I scrapped had two motors each, and some other fun parts (LCDs, microswitches, etc.).
Jeff.
--
Jeff Shirley
snipped-for-privacy@mindspring.com
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Jeff Shirley wrote:

Not that you'd do this, Jeff, but fax machines are also a great way to collect sensitive personal information about people and businesses. Most folks don't realize that many fax machines retain the numbers called, and the numbers received, including the ID stamps. This even after printing a journal. Erasing the memory isn't always straightforward. One business-level fax machine was known to have had in its memory complete copies of faxes it had broadcasted within the last several weeks of its use. Embarrasing to the law firm that had discarded the machine.
So the lesson here is: never throw out your fax machine. Take it apart instead. What you don't salvage do the Office Space routine with it. To music of your choice.
-- Gordon
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"Gordon McComb"

Hehehe, I love that music. Sometimes I have the same death wish on my computer.
Cheers
Padu
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[snip]

Excellent point, Gordon. And you are right, it is not something I would do.
Oh, I forgot about the SCSI storage expansion boxes I bought at a surplus sale at my alma mater. I was curious, so I plugged them into a Linux box to see if they had left anything on the drives.
I had a great time reading old student emails expressing some rather candid thoughts about a few of my professors. ;^)
Jeff.
--
Jeff Shirley
snipped-for-privacy@mindspring.com
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