Mechanical drive source?

Posted by ian dobson on June 16, 2006, 4:29 pm

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)

>>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.

> 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.
>

Posted by Padu on June 16, 2006, 2:24 pm

>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 ;)

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

Posted by on June 16, 2006, 2:51 pm

>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.

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.

>Look on ebay and surplus stores as you will find it even cheaper, but your
>specs must be flexible enough.

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.

Posted by Padu on June 19, 2006, 5:05 pm

> What do you mean with efficiency in this context?

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.

> I need precision (~10 mil). But speed or powerwaste is no big deal.
> My plan is something like 200x200 millimeter X-Y-Z board.

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.

>>Look on ebay and surplus stores as you will find it even cheaper, but your
>>specs must be flexible enough.

> 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.

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

Posted by Jeff Shirley on June 21, 2006, 11:11 am

[snip]

>>>Look on ebay and surplus stores as you will find it even cheaper, but your
>>>specs must be flexible enough.

>> 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.

> 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.

[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
spam-fried-rice@mindspring.com
"Bill Gates is filthy rich, but that doesn't mean I want to be married to him."

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