Re: Pulley Advice

Postby neels on Thu 26/May/16 9:19pm

Adding more pulleys (there's a proper name for that but I can't remember it) shouldn't make it harder, something is wrong.

For reasonably cheap you can get stainless bodied pulleys with nylon wheels that run on stainless bearings, should be as close to frictionless as you can get.
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Re: Pulley Advice

Postby philstar on Fri 27/May/16 12:32am

neels wrote:Adding more pulleys (there's a proper name for that but I can't remember it) shouldn't make it harder, something is wrong.

For reasonably cheap you can get stainless bodied pulleys with nylon wheels that run on stainless bearings, should be as close to frictionless as you can get.


block and tackle?

that sounds what i am looking for, where? how much?
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Re: Pulley Advice

Postby Sims on Fri 27/May/16 9:48am

Can we see a diagram? I used to use all dads sailing pullies to rig up double purchase systems as a kid. Get enough pullies attached to your tree house, and you can lift anything...
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Re: Pulley Advice

Postby philstar on Fri 27/May/16 11:11am

Sims wrote:Can we see a diagram? I used to use all dads sailing pullies to rig up double purchase systems as a kid. Get enough pullies attached to your tree house, and you can lift anything...




https://xkcd.com/857/

cant take photo of it now as i have take down the extra pullys to add geaease to them.
DSC_0133 s.jpg
standard set up 1
DSC_0131 s.jpg
standard down
washing line pullys.png
sketch of pullys
washing line pullys extra.png
extra pullys
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Re: Pulley Advice

Postby danose on Fri 27/May/16 12:52pm

stock setup is already a 2:1 z-pulley system, the 2nd photo will be 4:1 and is kind of ridiculous if you're already only seeing 4kg of load on the line (it's not like 4kg is much load), plus you'll be going mad with the amount of line you have to pull thru to raise/lower it (since the 4:1 decrease in force comes with having to pull thru 4 times the amount of cord compared to direct)

having a pulley as a re-direct with only 4kg of load is again crazy (if it was 40kg maybe - if it was 400kg a 4:1 system and bearing pulleys would be just the ticket).
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Re: Pulley Advice

Postby philstar on Fri 27/May/16 2:28pm

danose wrote:stock setup is already a 2:1 z-pulley system, the 2nd photo will be 4:1 and is kind of ridiculous if you're already only seeing 4kg of load on the line (it's not like 4kg is much load), plus you'll be going mad with the amount of line you have to pull thru to raise/lower it (since the 4:1 decrease in force comes with having to pull thru 4 times the amount of cord compared to direct)

having a pulley as a re-direct with only 4kg of load is again crazy (if it was 40kg maybe - if it was 400kg a 4:1 system and bearing pulleys would be just the ticket).


it is probably up to 8kg with the line fully loaded (8 kg washing machine/2 +water +empty 4kg load= >8kg) and i want it to be easy to pull. if the extra pulleys had not added more load into the system is would not have gone to 4:1.

if it was 400kg divided by 4 i would still just be climbing the rope (and I am a fat bastard). I think the small rope is contributing to the problem but it is needed to fit in the standard pulleys (but maybe i should try and find some 4-5mm rather than the 3mm i am using (it originally had ~4mm but i had to swap it out with to make it long enough to deal with the 4:1 pull))
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Re: Pulley Advice

Postby danose on Fri 27/May/16 2:47pm

philstar wrote:I think the small rope is contributing to the problem but it is needed to fit in the standard pulleys (but maybe i should try and find some 4-5mm rather than the 3mm i am using (it originally had ~4mm but i had to swap it out with to make it long enough to deal with the 4:1 pull))


so the additional pulleys you added on the frame/roof - are they all the same as the one you're using for your redirect? if so you're not only multiplying leverage - you're also summing up all that drag.

unless you switch to pulleys with decent roller bearings you're fighting a loosing battle of adding drag faster than you're gaining leverage - 3/4mm with 20kg of load over a sane diameter rod will not significantly increase drag, keep it simple, it's not like your raising the titanic
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Re: Pulley Advice

Postby Sims on Fri 27/May/16 3:18pm

Retardis question - But are the pulleys routed in the correct order?
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Re: Pulley Advice

Postby danose on Fri 27/May/16 4:33pm

Sims wrote:Retardis question - But are the pulleys routed in the correct order?


looks good to me

Image
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Re: Pulley Advice

Postby philstar on Fri 27/May/16 10:23pm

danose wrote:
Sims wrote:Retardis question - But are the pulleys routed in the correct order?


looks good to me




given that i am limited to pulling down
(excuse that i did not draw the rope going round the 2nd top pulley in the 2nd drawing)
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Re: Pulley Advice

Postby philstar on Mon 30/May/16 7:21pm

DSC_0157.JPG


friend offered to lend me this but i think it would be a bit much :)

greased pulleys seem to be working much better :) we will see how long the grease lasts.

tried running the rope through an eye bolt instead of a pulley, went up form 6 kg to 9 kg. double pulley is sitting at 3-4 unloaded
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