new linear drive system

[digital_life]

About this problem, i still didnt have the time to figure it out. but im thinking on a long "pulley" so the cable can move along it. (the size depends on the travel distance i guess)
any ideas????

[bigz1]

Would it be better,not to anchor the ends of the wire?

I was thinking maybe if you used to free wheeling axles of the same diameter of the motors at each end with the wire looped in the same direction and for tension join the wire ends with a small turnbuckle. The wire will still more lateral but it wont effect the accuracy because it will be moving lateral on the idle axles at the same time.

Using this sort of system what would be the maximum distances could you expect to travel?

[digital_life]

BIGZ1, if you use freewheling at the ends, it wont move, it will just rotate and dont produce any linear movement .... im i right? or maybe i didnt understand you at all!
any graphic to upload?

[bigz1]

You got me. Thats the sort of genius you get the morning after an England victory in the World Cup(no hand of God to stop us now). Plus its very hot at the moment.

But bear with me. How about using the same setup. This time anchoring the ends of the wire to a micro linear bearing with an 1" of travel(usually go for $10 on ebay). This would have to be attached to the part you wanted to move. . I will try and draw something but life is a little hectic at present as I am expecting to be a father again VERY SOON.

[digital_life]

with your setup, i think you will have some friction (not the necesary) loss on wire itself. i will turn and wont translate any move to the piece.

i think that the stepper should be mounted and fixed on the part itself. so on the very same axys of the stepper, one should mount a pulley with 4 to 6 turns of wire arround it.. just like the detail picture of the telescope transmision system.

we need about 79.79 mm of wire lenght for each turn in 1" diameter pulley, so in 5 turns arround it , we have 398.9832mm.
ok. supposed that the wire is 1mm diameter, we need 1.4 meters to have 1 meter displacement . and we`ll have a 10mm variation at the pulley, from end to end.
so in the pulley we should have a 12mm groove (*) to let the wire enaugh room to move side to side while turning all the way (end to end)
it doesnt need any compensation , as the wire will move itself, from turn to turn...
and then come back to its "original " position, as we reverse the turn direction.

(*) 12 mm grove or "thread alike" so the wire can we wrapped with some sort of guide.

im i clear? im i right about it ????

[thekm]

I'm digging this drive system. Would have to be the cheapest out there. My trials will most likely use the big spool of heavy woven kevlar thread... some 250lbs strength per line... I'm thinking the thread may be more grippy than wire line.... but I sure to have enough to through some away on trials

(can buy very large spools on ebay for $25... and I bought it already for composite construction, and it's very handy stuff)

[wjfiles]

Just a thought,
Could a toothed belt be used instead of wire. I am led to believee that there are belts with almost no stretch.

[thekm]

Originally Posted by wjfiles Just a thought, Could a toothed belt be used instead of wire. I am led to believe that there are belts with almost no stretch.

Yup, been looking into them recently. They all don't stretch, but you can pick what they're woven with, nylon, kevlar etc. But they have a cost that is higher than cheap drive screws, and approaching what appears to be the good middle-ground of drive screws. A belt the length for a 4 foot table is $29, with $10 for a pulley, so you're up running around $50 an axis, more if you figure tensioner pulleys or whatever.