How to draw sprockets?
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I have been driving myself slightly nuts trying to draw sprockets for use in a "supermileage car" transmission. (It's a lightweight vehicle to be built by my granddaughter's school for entry into a competition to see who can do the best gas mileage). There is fairly heavy use of bicycle componentry including chains and the sprockets which are giving me problems. I want to draw them faithfully so have calculated the correct Pitch diameter etc and set out a proper tooth profile (this is probably overkill and where it starts to go wrong!). So far I have come up with a couple like those below but they have taken longer than I would like.
The two shown have been done in different ways - the small one by creating a "tooth and socket" pair, shaping the top of the tooth then array copying it around the Pitch circle. This has promise but the tooth and socket pairs don't match exactly, leaving tiny gaps that need to be filled in and that takes quite a while. I am sure there must be a better way but so far haven't found it. The larger one, I made as a single piece but still found gaps that needed filling and then I started to shape the top of the teeth one at a time but that is just too much like hard work, so I gave up on that approach.
I'd be grateful for any pointers!
Chris
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These look pretty good.
Are you working in real world scale, or have you enlarged the model to avoid tiny faceless triangles--that is, if this has any thing to do with your difficulties.
Watch out for the Sketchup segmented "circle" problem. Otherwise, I have no clue where the problem lies.
I imagine that some respondents would like to see your skp file so they can "ferret out the gremlin". -
Hi Chris,
You have the right idea by creating a "tooth and socket" pair, but if you make them into a component before you rotate an array, when you edit one component to make it fit all components will be updated.
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Thanks guys for the suggestions. I think the problems do arise largely from Sketchup's distaste for small stuff as it definitely went better when I scaled the things up. I also need to overcome the expectation that it will behave like a full blown solid modeling CAD program as in truth I am not going to be using these drawing for any manufacturing - just as a guide to what goes where. The nature of the project is such that a lot of it will be done by youngsters on a trial and error basis any way.
For anyone interested, I attach the models.
Chris
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Hi Chris,
I am sure it could be a great fun for these youngsters once you have overcome these little problems. Have a look at this video below - it was modelled and animated entirely in SketchUp with the SketchyPhysiscs plugin (then rendered and exported as a video in Twilight render - but if you do not mind the watermarks, as a school project, its free demo version would also make it)
[flash=560,300:19pv9cls]http://www.youtube.com/v/q3Lp-fAg0oM&hl=en_US&fs=1&[/flash:19pv9cls]
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Gai,
That is indeed impressive! Thanks for the link.Chris
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