I'm experimenting with intermittent motion. I'm trying to make a counter so I want a wheel to turn a tenth of a turn each time I turn the handle on my model. Two things - the display wheel turns 36 degrees each time I wind the handle - second, after ten increments I'll need an output of some sort that can be passed onto another counter. That way I should be able to stack counters and count up in tens, hundreds, thousands...
The picture left is my first attempt. Two ten teeth gears, one with all but one teeth removed, the other with the teeth trimmed. I generated the gear profiles here, imported them into Illustrator and edited the profiles.
Having tried out the profile by pinning it onto a piece of foam board (top picture) I created a 3D version. Only the single tooth piece was 3D - the other gear was made with a double thickness of card. Time to test.
Didn't work.
The problem being the perennial one of cardboard engineering, tolerance. As the single tooth gear turned, it caught on the other gear turning it prematurely. I can't see a way round this (any ideas?) It would word fine in metal or wood with proper bearings but not with card. Next - I'm now trying a pawl drive. More news soon.
Tuesday, October 30, 2007
Intermittent Motion
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Paper animations by Rob Ives.
6 comments:
Look out below? Perhaps position the one-toother on a lower plane than the other, and fold the "tooth" upward so it doesn't interact at all until you want it to? You could make it an extra-long tooth that could fold back on the wheel and attach to it...
Car odometers use an intermeadiate gear, mainly to make the indicator gears turn the same way, but driving a smaller diameter gear might reduce the tendancy to catch on the toothless part..
Regarding the intermittent drive.
Why not use a smaller root circle radius on the single tooth gear but leave the single tooth as the same radius as before...
Let's say that both wheels have a 4cm radius.
Using gear nomenclature as per Wikipedia image http://en.wikipedia.org/wiki/Image:Gear_words.png
The height between the bottom land and top land is 0.5cm
The root circles will each have a 3.5cm radius.
The distance between the two gears is 4+4-0.5(mesh) = ~7.5cm (allowing a little to ensure no binding)
Make the root circle of the driver (single tooth) to be 3.3cm instead of 3.5 and keep the outside (addendum) circle at 4cm. Keep them at the 7.5cm separation.
There will be a 2mm gap between the root circle of the driver and the teeth of the driven and this should be enough so that it does not snag. Yet the teeth should still engage.
Also, your teeth are a bit square, you may wish to soften them slightly by using a shallower angle.
ie not __|''''''|__
instead __/''''''\___
Hoping this helps.
Regards,
Keith.
I'm working on something similar, and had some success. Difference being I meshed the gears at a 90° angle, and used round teeth.
Blog Entry with pictures here
ok... chemcial enginner.. not mechanical.. BUT.. how about giving the left gear (the one with more toonts)a little more width (its waaay too thin)
then... the angles of the teeths could be a lil smoother... (not 90 but 85 mb?)
and last.. try using a "cover" on the uni-toothed gear... so that the edges arent paper borders..
thats it..
thanks for everyting...
I don't know if this will be any help, but have you taken a look at clockwork escapements?
They are simple, yet amazing (amazingly simple?).
The 'Eureka!' is similar to the answer of the riddle you feel you should've known.
Maybe off base, considering a hand power drive, but check it out!
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