new linear drive system

[rceebuilder]

I was using 8 mm metric screw to drive the axis of my small router The speed was not so disturbing for a small distance The max jog speed was about 6 mm per sec .Then I built a new router with a 1 meter long X axis but now I have a new problem :low jogging speed. I checked the cost of ball screw , rack pinion and belt drive but all of them require usd 100 per axis. So I decided to try steel wire drive method .I have tensioned a 0.2mm steel wire and wound it on a 8 mm steel shaft at 3 turns. With this way the motion transmission is perfect and there is no backlash at all.The only problem is linear motion of the drive shaft .When the shaft is turned it is forced to move axialy too .it is because of the wound effect of the wire. I hope I could describe what I mean . May be this picture help. The shaft will be directly driven with a step motor. Do you have any idea to compansate the linear motion of the shaft?

Murat..

[chuckknigh]

Yes -- the screw is moving 1 thread laterally, per rotation. If you mount the screw on a nut, and then allow the whole thing to move laterally, the entry and exit points for the wire will remain constant.

A similar idea cropped up on DIY-CNC a while back. You might check the Yahoo archives.

-- Chuck Knight

[davesaudio]

solid wire?
Has anyone determined the wire life span?
D

[rceebuilder]

it works on some photocopy machines more than 10 years.

[zoltan]

Rceebuilder,

You made me curios. I do not understand very well your system. Could you, please, get in more details? Eventually a sketch will be helpful.

Thank you,

Zoltan

[rceebuilder]

Zoltan , Here is the 2 type of wire driven gantry project. Of course the wire will be plied type. The only problem is how to compansate drive shaft's lateral movement.

[Charlye]

rceebuilder,

If you are going to directly drive the 8mm shaft with a 1.8 degree/fullstep motor then you'll get 0.1256mm (0.0049 inch) of linear motion per step. With micro stepping it gets slightly better. 8mm rod with 0.2 m wire you can drive 600mm of linear motion with only 24 full rotations.. so that's only 5mm of lateral motion. Is that fatal?

I'm looking seriously at using the looping wire system on my first machine, which will be a simple 2d plotter and foam hotwire cutter.

Of course going with a small diameter drive rod gets better resolution, but more wear and tear on the wire and even more lateral movement.

Playing around with numbers I found that using a 1/4 inch drive rod results in a ~0.1mm step (0.0997mm but who's counting). Using English parts to get metric motion, a bit funny.

Ideas for the lateral movement.. I like Mr Knight's idea of using the nut and threads. If your steel wire 'threads per inch' matched that of available nut/screws you'd be all set. Changing the gauge of the wire can help get you there.

Charlye

[geoff p]

How about setting the drive shaft at an angle to the wire: you know the diameter of the wire and that of the shaft, so calculate the angle, and squint the beast a bit. I used to do this on a home-made machine of very limited travel. It might work for you!
Or set two small ball-races, one each side of the shaft, to force the wire to enter-and-exit the helix where you want.

[Netjams]

Originally Posted by geoff p How about setting the drive shaft at an angle to the wire: you know the diameter of the wire and that of the shaft, so calculate the angle, and squint the beast a bit. I used to do this on a home-made machine of very limited travel. It might work for you! Or set two small ball-races, one each side of the shaft, to force the wire to enter-and-exit the helix where you want.

That will work

[rceebuilder]

I applied it to my 40" x 20" router in x and y axis . The result is awesome . Particularly I liked gantry speed. Precision is enough for me. I will send some pictures soon.

Murat..

[dkowalcz]

You could use allthread, no? A 3 foot piece of 1/2" dia is about $5 USD, and add 35 cents for a nut. Not the greatest setup, but I think it'd be more reliable.

[dkowalcz]

It occurred to me that my other post could be construed as rude, so I'll add that MIT used wire drives in some of their experimental robots.

The idea was to get force transfer from a small shaft (eg, the motor) to a larger shaft (eg, an arm joint) with no backlash, and cheaply. Very clever design.