Pullies Vs Gears

[John HaineParticipant @johnhaine32865]

Posted by jason udall on 07/10/2016 10:26:07:

250/36/60/60 = 1.9 mW
…
.

Autowind! Lift the weight with a little geared motor once a day.

Simples.

[SillyOldDufferModerator @sillyoldduffer]

Any reason why Izack shouldn't use a pulley system arranged 'in reverse' and suspended from the ceiling like this?

Proportionally more weight will be needed to maintain the pull on the clock drum. It will be necessary to add a significant allowance for friction. (5 pulley axles!)

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Haine on 07/10/2016 10:32:52:

Autowind! Lift the weight with a little geared motor once a day.

.

As per my post referencing the 'Basic Clock' thread

MichaelG.

[Izack MaddParticipant @izackmadd89335]

Posted by SillyOldDuffer on 07/10/2016 10:49:09:

Any reason why Izack shouldn't use a pulley system arranged 'in reverse' and suspended from the ceiling like this?

Proportionally more weight will be needed to maintain the pull on the clock drum. It will be necessary to add a significant allowance for friction. (5 pulley axles!)

Dave

This is approximately how it was envisaged with the gears between the pullies and the drum. And as the drum onlyhas to turn at a speed of 1rpm and the weight has a potential speed of 32 feet per second even reducing that by a factor of five still gives me 6rpm. And a pulley ratio of 4:1 so I'd have four times the travel and enough speed. And by gearing down as with a cars gear box I'd increase the force enough to turn the other gears in the clock. Or so I thought.

[Izack MaddParticipant @izackmadd89335]

Posted by jason udall on 07/10/2016 10:26:07:
Just in case anyone intrested..
2.5 kg .. rough terms 250 N
Falling through say 1 m
Is 250 J oules…
In say 36 hours…
250/36/60/60 = 1.9 mW
…
.

?…

[Izack MaddParticipant @izackmadd89335]

Posted by jason udall on 07/10/2016 10:15:39:
Here's a thought…this chaps lead weights only 9.5kg …where current esitmates are around 200 kg…
This would give a density of 9.5/200 *11 or 0.5 mmm…nice metal you have there…does it float on water by any chance?…

So what…

[Izack MaddParticipant @izackmadd89335]

Posted by jason udall on 07/10/2016 10:15:39:
Here's a thought…this chaps lead weights only 9.5kg …where current esitmates are around 200 kg…
This would give a density of 9.5/200 *11 or 0.5 mmm…nice metal you have there…does it float on water by any chance?…

Not relevant

[Izack MaddParticipant @izackmadd89335]

Posted by jason udall on 07/10/2016 10:06:37:
Re weight/size.

Well I have density of lead as 11 gramme/cc
Or 11 kg/litre
A litre is 100 mm cube

300x250x450 would by my reconing be about 33 litre 371kg 3/4 of that say 200 kg…:O

That's nice to know know deal with the question

[Izack MaddParticipant @izackmadd89335]

Posted by Michael Gilligan on 07/10/2016 10:04:13:

Posted by Izack Madd on 07/10/2016 09:21:53:

Posted by jason udall on 07/10/2016 08:49:06:
Btw…my estimate of ten kg of lead is less than a liter

100x100x100 mm

The lead I've got 75% fills a box 300 x 250 x 450 mm and that only weight 9.5kg. So I must have been sold a pup and it's not lead. But it looks like lead and it weighs the same and melts the same. So…

.

A quick 'sanity check'

In big units: the density of lead is given as 11340 kg per cubic meter

To keep things simple … What is the weight of a 250x250x250 mm block ?

11340 ÷ 4 ÷ 4 ÷ 4 = 177.1875 kg

i.e. … Roughly the weight of two people.

MichaelG.

.

Edit: Russell beat me to it.

Edited By Michael Gilligan on 07/10/2016 10:08:37

Big deal. Check the name. Sanity doesn't come into it

[Izack MaddParticipant @izackmadd89335]

Posted by Russell Eberhardt on 07/10/2016 09:58:15:

Lead weighs 11.34 g/cm³ so 11.34 x 30 x 25 x 45 x 0.75 = 287,000 g, about a quarter of a ton! How did you lift it?

Russell.

With high hopes

[Izack MaddParticipant @izackmadd89335]

Thanks for those that were adding helpful comments. All the others sorry you wasted your time.

I'm now considering this subject closed as I'll deal with it the hard way. Experimenting and learning not criticism.

[Izack MaddParticipant @izackmadd89335]

Posted by John Haine on 07/10/2016 09:46:12:

It's not a torque issue! What matters is the energy used. If you geared down to recover the torque, the output end of the gears would run 4 times slower, so the weight would have to fall four times further for the same running time. So you would still need 4 times the drop if you stay with a 2.5 kg weight. As has been said you really need to reduce the energy used by the clock, dissipated in friction. There are several designs for wooden clocks around that used ball races for critical pivots. Neither gears nor pulleys "increase power" they only lose energy, but they can change torque and speed. Power delivered is (loosely) torque x speed.

What is needed is not speed but potential energy in the form of turning force and speed of the turn. Which loosely equate to torque

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Izack Madd on 07/10/2016 09:21:53:

But it looks like lead and it weighs the same and melts the same. So…

…

… So … Please review what YOU have written, before being so rude to we who are trying to help.

[jason udallParticipant @jasonudall57142]

OK.

The op needs say 2.5 kg weight ( yeah I know kg is mass but lets skip that fir now) hanging on string. ..falling say 1 m
It does this in 1.5 days.
He needs 4 m of fall in 8.5 days.
Apart from needing a winding drum in the clock to hold 4 m of string..
A simple block system with four times the weight would work.

If comments along the lines of “are you sure your over a cubic foot of metal really only weighs 2.5kg” are un helpful… well sorry to have spoken.
Good luck and farewell

[SillyOldDufferModerator @sillyoldduffer]

Posted by Izack Madd on 07/10/2016 10:58:57:

Posted by SillyOldDuffer on 07/10/2016 10:49:09:

Any reason why Izack shouldn't use a pulley system arranged 'in reverse' and suspended from the ceiling like this?

Proportionally more weight will be needed to maintain the pull on the clock drum. It will be necessary to add a significant allowance for friction. (5 pulley axles!)

Dave

This is approximately how it was envisaged with the gears between the pullies and the drum. And as the drum onlyhas to turn at a speed of 1rpm and the weight has a potential speed of 32 feet per second even reducing that by a factor of five still gives me 6rpm. And a pulley ratio of 4:1 so I'd have four times the travel and enough speed. And by gearing down as with a cars gear box I'd increase the force enough to turn the other gears in the clock. Or so I thought.

I find the relationship between energy, force, work, speed and torque confusing!

In this case, the way I look at it is:

• You need sufficient force on the clock drum to turn the clock's mechanism. The force will be provided by a weight. As the clock regulates its speed you don't have to worry about speed, you just need to provide enough pull or 'weight' on the clock's winding drum. You know what the clock weight is.
• The pulley system has a ratio that could be used to extend the distance that a new winding weight will fall. This will make the clock run longer between rewinds, provided the clock drum is still pulled hard enough to work the mechanism.
• Assuming a frictionless 4:1 pulley system, increasing the effective length of the drop by four will also have the effect of reducing the effective weight at the clock by a factor of four as well. So the pulley weight has to be 4 times heavier than the original clock weight in order to provide the same 'pull'.
• As a real pulley system is far from frictionless, the pulley weight will probably have to be distinctly more than 4 times bigger. 6 times feels more like it, but you'll probably have to experiment to find a pulley weight that keeps the clock going consistently/

Your original proposal to use gears to restore torque reminded me of the way transformers are used in power distribution systems to step voltages up and down. As such I initially thought it might work, but that was due to me ignoring the fundamental restrictions that forbid perpetual motion.

Good luck with your clock,

Dave

[Sam Longley 1Participant @samlongley1]

Posted by Izack Madd on 07/10/2016 10:59:30:

Posted by jason udall on 07/10/2016 10:26:07:
Just in case anyone intrested..
2.5 kg .. rough terms 250 N
Falling through say 1 m
Is 250 J oules…
In say 36 hours…
250/36/60/60 = 1.9 mW
…
.

?…

Personally i would use a witch

According to sir Bedovere they are heavier than a duck

[Martin KyteParticipant @martinkyte99762]

as I said

"If you really want to be lazy.

Fit a pulley to the floor and another to the ceiling. Run the clock line down to the floor round the pulley up to the ceiling and thus to the weight. You then have the full height of the room for the drop."

This just increases the drop and thus the going time.

regards Martin

[Neil WyattModerator @neilwyatt]

Posted by Izack Madd on 07/10/2016 08:55:25:

Posted by Neil Wyatt on 07/10/2016 08:41:14:

The energy (potential for doing work) available is the weight multiplied by the distance it drops.

If you want to get the clock to run for longer, you have to reduce the work required to operate it – any change of puliies/gears/driving arrangements won't get you round the basic physics or otherwise you would be on the way to perpetual motion.

So… the best you can do is look very critically at each moving part in your clock and see if it can be improved to reduce friction. Did John Harris use lignum vitae or some other very hard oily wood for pivot bushes? Do you have teeth that could be brought to a better finish? Could you incorporate a ball bearing in the most heavily loaded pivots?

Neil

Hi Neil

I realise that I can't get back all the energy hence the reference to torque not speed. As I would be sacrificing speed to balance the equation and so it's not a perpetual motion device. Yes Harrison used Lignum Vitae for his bushings as well as some very complicated gear construction to compensate for humidity. Such as putting odd shaped pieces of different wood at angle to the growth rings. The original plans that have it running for just 1.5 days uses bearings and such likebut to still at its limit of power input to torque output. Once the power has gone through all the gears as they have to gear down the power as it's the number of teeth that's important. Not the torque as with a normal gear box.

My thought was as the speed is regulated by the mechanism not the drive force then the speed of the primary drive wouldn't matter so long as its faster than the minimum rpm the clock creates. Rather than the drive setting the speed.

I'm still baffled as to why gear can't compensate the loss of torque. As they seem to increase in power when geared up but loose speed. Which is fine. And would negate the problem of the loss of power of the increased travel of the weight on the pullies.

Because if you sacrifice speed to gain torque, you then have to gear up again or the clock will run slow, so and all the extra torque is lost…

Neil

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