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Amnon,
I've also found a not in-significant source of friction is the bushes
against the beams (or whatever your axle goes through). I've reduced this a
bit on occasion by not using bushes to hold axles in position, but having a
brick at each end, that the axle (almost) butts up against. It does allow a
bit of length-wise motion, but reduces the friction.
ROSCO
Amnon Silverstein <amnon@best.com> wrote in message
news:G526GG.IKB@lugnet.com...
> One of the tough problems in building a clock is to design a very low • friction,
> very tall gear ratio drive. I want the spool to turn around somewhat less
> than once every half hour, and the escapement to turn once every six • seconds,
> so I need around 1:350 drive. I've been using:
> 8:24 -> 8:40 -> 8:40 -> 8:40 = 1:375
> For every one turn of the spool, all of the axles in the drive train make • a
> total of:
> 1+3+15+75+375 = 469 axle turns worth of friction
> Also, I can total up how many times a pair of teeth mesh each time the • spool
> turns:
> 24 + 120 + 600 + 3000 = 3744 geartooth meshings of friction
>
> I would really like to reduce the friction. I am going to try to use the • large
> turntables fitted with plates to make axle holes. This could give a train • like:
> 8:56 -> 8:56 -> 8:56 = 1:343
> 1+7+49+343 = 400 axle turns worth of friction
> 56 + 392 + 2744 = 3192 geartooth meshings of friction
>
> So this drive train should have about 15% less friction.
>
> If Lego provided a huge 2800 tooth gear, I could have a system that • reduces the
> friction another 13% or so:
> 8:2800 = 1:350
> 350 axle turns worth of friction
> 2800 gear tooth meshings worth of friction
>
> Lubrication might help, but that is a sort of non-Legoy solution, and I am • not
> sure what to use. Maybe a dry lubricant like graphite or spray teflon • would be
> best.
> Any suggestions for designing an efficient drive? Am I analyzing friction
> correctly?
> Reducing the friction and improving the energy transfer of the escapement • would
> lead to the most dramatic improvement, but this is really tricky.
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"Ross Crawford" <rcrawford@csi.com> writes:
> I've also found a not in-significant source of friction is the bushes
> against the beams (or whatever your axle goes through). I've reduced
> this a bit on occasion by not using bushes to hold axles in position,
> but having a brick at each end, that the axle (almost) butts up
> against. It does allow a bit of length-wise motion, but reduces the
> friction.
The length of one axle is normally slightly shorter than a corresponding
beam, ie. an axle #4 is slightly shorter than a 4 stud beam. So this is
probably why you achieve some slack when putting bricks on either side
of the axle to support it.
But wouldn't your solution be analogous to using bushes to support the
axles, but letting there be some slack between the bushes and the
supporting structure? It appears to me that the effect of this would be
the same as the effect of removing the bushes completely.
Fredrik
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Fredrik Glöckner <fredrik.glockner@bio.uio.no> wrote in message
news:m3k89e4iva.fsf@crossblock.localdomain...
> "Ross Crawford" <rcrawford@csi.com> writes:
>
> > I've also found a not in-significant source of friction is the bushes
> > against the beams (or whatever your axle goes through). I've reduced
> > this a bit on occasion by not using bushes to hold axles in position,
> > but having a brick at each end, that the axle (almost) butts up
> > against. It does allow a bit of length-wise motion, but reduces the
> > friction.
>
> The length of one axle is normally slightly shorter than a corresponding
> beam, ie. an axle #4 is slightly shorter than a 4 stud beam. So this is
> probably why you achieve some slack when putting bricks on either side
> of the axle to support it.
>
> But wouldn't your solution be analogous to using bushes to support the
> axles, but letting there be some slack between the bushes and the
> supporting structure? It appears to me that the effect of this would be
> the same as the effect of removing the bushes completely.
The difference is, when the bush is rubbing against the beam, it's a much
greater surface area than when the axle-end rubs the end-stop.
ROSCO
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