Smarter way to align a belt around a wheel

Grobe · Postby **Grobe** » Fri Sep 09, 2011 2:37 am

Hi.

I sometimes draw physics figures. When I have multiple wheel and a belt going around in any direcction, i use some time to adjust the path to align into the wheels until I'm satisfied.

But I ask for a more creative solution. I assume adjustment always will be needed, but is there a smarter way to achieve a near perfect alignment of the belt on the wheels with less work?

Thanks

: beltWheel_example.png (52.62 KiB) Viewed 12303 times

RobA · Postby **RobA** » Fri Sep 09, 2011 4:17 am

The development CAD tools would have helped as the belts are just tangents to the circles in all cases.

Too bad the CAD tools were never finished.

-Rob A.

Grobe · Postby **Grobe** » Fri Sep 09, 2011 4:34 am

Yes, that is too bad :cry:

In meantime (or eternity) there should be some clever ways to use guides to make this happend. Question is how...

Postby **brynn** » Fri Sep 09, 2011 4:50 am

Well I guess it depends on your preferences and drawing habits, and whether the wheels have to have some precise alignment. But you could use Guides. Or I'm thinking you might even find a way to use the Star shape.

With Guides, you can create a guide at any angle. First pull a guide out of the rulers, then highlight it and double-click on it. In the dialog that comes up, you can adjust the angle, and thus make a guide that touches the edge of 2 circles. Using that, you can make a node on each circle where the guide touches it, or otherwise use the guide to mark the line between them.

I'm thinking with the Star tool, 3 points, and switching to polygon, then use....I think it's either Shift or Alt, you can make the points rounded. Or on the control bar. Then I don't know....maybe make 3 of them of different sizes, and somehow combine each rounded corner, and then draw circles (for wheels) to match each rounded corner. Actually I think guides would be the better approach....

Or maybe you could use the rounded triangle from the Star tool, and do object to guide? I'm not sure how that would work. But it would be worth a little experimenting, I think

Grobe · Postby **Grobe** » Mon Sep 12, 2011 9:03 am

Hi.

Still working with this. I have a plan how to achieve a perfect match. But I just get a problem to solve first. I have to get a node to snap to intersection between guide and path/circle. When this is achievet I will try to post a little guide

[edit]
I've chechked out an old thread I wrote some time back - Snap to guide/path intersection.
Problem here is that the workaround I fount that time only work if guide is perfectly horisontal or vertical. This is not the case now

Postby **brynn** » Mon Sep 12, 2011 5:31 pm

Hi Grobe,
It would be pretty easy, with snapping, to draw a straight path (2 nodes) directly over the guide. Then you would be able to snap to the path intersection. That path can be deleted or hidden afterwards.

Grobe · Postby **Grobe** » Mon Sep 12, 2011 11:34 pm

brynn wrote:Hi Grobe,
It would be pretty easy, with snapping, to draw a straight path (2 nodes) directly over the guide. Then you would be able to snap to the path intersection. That path can be deleted or hidden afterwards.

Well, I also had that idea about using straight lines. However - I couldn't get that to work either.

The latest method I tried was to use Dynamic Offset. This worked great for ONE wheel. But to align the "belt" around the other wheels wasn't that easy. One step baahead and two steps back

[edit]
I think I start to move toward a possible solution now. I've made 3 wheels and 3 triangles where corners is placed at center of each wheel. Then I did Outset each of the triangels so they fit outside each wheel.

Further plan is to move the points of one outset triangle to match the other triangles nodes. But I just got a new problem. Some of the nodes from one soft triangle wont snap to nodes of another tringle, even if snap to cusp nodes and snap to soft nodes is activated.
It could be a result of me using Inkscape 0.48+devel r10611 (beta version).

RobA · Postby **RobA** » Tue Sep 13, 2011 1:21 am

I put together a jessyink slideshow on how to geometrically construct tangents to two circles using inkscape snapping:

http://www.silent9.com/incoming/belt.svg

More accurate, but certainly NOT less work

This is how I leaned to draw with a compass, ruler and drafting triangles...

Here is the final result:

: belt.png (27.6 KiB) Viewed 12221 times

-Rob A>

Grobe · Postby **Grobe** » Tue Sep 13, 2011 3:22 am

Thanks a lot for a nice guide RobA. Ten points direct to you

I can live with circle diameter isn't snappable. Just a comment to that - when drawing a line that snap to paths intersection, you would get a very precise reading of it's length in status bar. Remember this lenght (or write it down) and set circle diameter to be twice that lenght.

Just remember to set stroke to none for the circle, since there is a resizing bug affecting all objects htat have a stroke width > 0 (can't find that bug right now)

dvlierop · Postby **dvlierop** » Wed Jan 18, 2012 5:55 am

Things have become quite a bit easier, as demonstrated in this movie http://www.diedenrezi.nl/SnapTangentially.webm. As of revision 10866 (see http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/10886), Inkscape now tries to snap to paths both tangentially and perpendicularly... but only if "snap to paths" has been enabled, and it cannot be toggled on/off yet.

Please realize that if you try to snap two opposite ends of a single line tangentially, then only one can be truly tangential at any time. That is because if you snap the first end tangentially and subsequently move the second end then the first end will have lost it tangentiallity. This will likely not be a big problem though as it will converge quickly if you iterate a few times over the opposite ends (have a close look at the movie to notice this). This will be fixed in future revisions by enabling tangential and perpendicular snapping in the selector tool, such that one can rotate a line and still have it snap tangentially.

Have fun!

Grobe · Postby **Grobe** » Wed Jan 18, 2012 6:18 am

NICE

That is a feature that I have being awaited for a long time.

Too bad 871792 prevents me from effectively using latest beta versions on W7.

dvlierop · Postby **dvlierop** » Wed Jan 18, 2012 6:39 am

Are you user "pRototype" in that bug report? If not, then please drop a note there saying that you have this issue too. It hasn't been confirmed yet by others, e.g. people not having a Norwegian GUI language. That might help in bumping the priority a bit.

chriswww · Postby **chriswww** » Thu Jan 19, 2012 1:08 pm

been looking at this, and found another possible way:
select all circles and Extensions->Generate_from_path->Interpolate. Using suitable number of steps (use live preview) so that the inerpolated circles all overlap somewhat. Do the interpolation again from last circle in the series back to the first circle. Now select all the interpolated circles, which will have been created as groups. Ungroup them, and whilst all of them are still selected, Path->Union. Now do a suitable outset, duplicate and inset the duplicate, and difference the two. Now all that's left to do is to draw a solid black shape over the extra triangle in the middle, and difference the outline (belt) with that black shape. Should end up with perfect fitting "belt" around the circles. might help during the operation to move the original circles out of the way, for convenience in selecting objects. if the "belt" object seems to bite into the circle "wheels" too much, just resize whilst holding down control and shift keys, to resize in all directions uniformly from center.

Postby **druban** » Fri Jan 20, 2012 12:14 am

Since this topic is still active I thought I'd put in my ten cents....

: rect1233.png (250.78 KiB) Viewed 12014 times

chriswww · Postby **chriswww** » Fri Jan 20, 2012 11:14 am

love the illustration there Druban. the pictures almost come to life.
i found that you can also get the tangent only by:
- draw a rectangle. one of the long edges will become the tangent.
- select circle/elipse drawing tool, and turn on snap to bounding box.
- draw one circle (with control key pressed) by starting on a snap point on the rectangle edge, dragging out to desired size
- likewise draw a second circle, starting further along the rectangle edge.
- use bezier tool and have the right snap options turned on so that you can start a line and finish it on the rectangle edge, with the ends coinciding where the rectangle edge and circles' perimiters intersect.
Now you can delete the rectangle, duplicate and mirror the tangent line appropriately, so it forms the opposite side tangent. group all objects and set on desired angle, etc.

fizzcat · Postby **fizzcat** » Fri Jan 20, 2012 7:18 pm

I take it that from RobA's comment that "CAD" tools were planned for Inkscape but never implemented. Is this still a current development? A slight improvement in the snapping would make life a lot easier, as well as being able to specify line lengths, preview of snappings etc. the usual really basic CAD tools that old time tech illustrators use all the time. I don't want to go back to a CAD system but I do miss some of the things I could do even on a drawing board with a compass and ruler!

I'm guessing that this has been requested before but there are no developers interested in this rather uncool stuff.

~suv · Postby **~suv** » Sat Jan 21, 2012 4:36 am

Off topic:

fizzcat wrote:I'm guessing that this has been requested before but there are no developers interested in this rather uncool stuff.

That's really the kind of talk to get them interested, indeed.

Any of you even bothered to read Diederik's earlier comment?

(Hint: basic tangential and perpendicular snapping has landed in the development branch (more to come - it's work in progress and will be part of the next major release 0.49). Development snapshot builds for testing on Windows as well as PPAs of current trunk (nightly builds) for Linux are available in the usual places.

Postby **druban** » Sat Jan 21, 2012 6:08 am

fizzcat wrote:I do miss some of the things I could do even on a drawing board with a compass and ruler!

Inkscape has had a ruler for a while, and positionable guides. The elliptical tool is better than a compass ever was. What particular things do you miss? It is often just a matter of rethinking an approach. The erasing, smudging, crinkling and spilled coffee are probably pretty far down on the list of things to incorporate into Inkscape.

~suv wrote:Any of you even bothered to read Diederik's earlier comment?

Of course, this particular problem has an easy solution in the latest development version of Inkscape. In particular the perpendicular snap saves an awesome amount of workaround time. I just wanted to offer my rigorous geometric construction. I have an unfortunate pedantic streak in my character!

~suv · Postby **~suv** » Sat Jan 21, 2012 6:14 am

With a recent development version, here's a schema how to create a tangent between two circles

: tangent-between-2-circles-screenshot-schema-1.png (27.89 KiB) Viewed 11953 times

(once the line from the midpoint of the smaller circle to the tangent snap-target on the auxiliary circle has been drawn, the rest is easily constructed by duplicating and moving the line segments - if preferred, with help of guides. The radius of the auxiliary circle = radius of larger circle - radius of smaller circle)

Attaching another sample file (the belt itself is drawn making use of the spiro path effect for the arcs - a 3-node spiro spline sub-path with a smooth node in the middle draws an arc through 3 points):

~suv · Postby **~suv** » Sat Jan 21, 2012 6:20 am

druban wrote:Of course, this particular problem has an quick and easy approximate solution in the latest development version of Inkscape. In particular the perpendicular snap saves an awesome amount of workaround time. I just wanted to offer my rigorous geometric construction. I have an unfortunate pedantic streak in my character!

I disagree: see my earlier post for an easy way to construct the tangent precisely, not approximatively.

Postby **druban** » Sat Jan 21, 2012 6:21 am

Yes! I edited my post to remove the 'approximate' after seeing your construction! We are cross posting!

I was referring to the comment in D's post:

Please realize that if you try to snap two opposite ends of a single line tangentially, then only one can be truly tangential at any time. That is because if you snap the first end tangentially and subsequently move the second end then the first end will have lost it tangentiallity.

I realize that the construction of the necessary trapezoid is easier with the tangent snapping feature! (Although when drawing the circle from the center of the large circle I was unable to find a snap to the circumference of the smaller circle that would give the radius R-r, what did I miss? Wait, you centered the small circle on a node, right? So path-to-path snapping still not available...)
Everyone will of course have noticed that ~suv and I have constructed exactly the same quadrilateral, but using different methods! Think Leibniz and Newton! Edison and Tesla!

P.S. I know you don't actually have to construct the quadrilateral in your method, ~suv, and it's just there to show relative size!

~suv · Postby **~suv** » Sat Jan 21, 2012 7:32 am

druban wrote:I realize that the construction of the necessary trapezoid is easier with the tangent snapping feature! (Although when drawing the circle from the center of the large circle I was unable to find a snap to the circumference of the smaller circle that would give the radius R-r, what did I miss? Wait, you centered the small circle on a node, right? So path-to-path snapping still not available...)

How to construct the auxiliary circle:

duplicate smaller circle
move the duplicated circle and let its midpoint snap to the right quadrant point of the larger circle
drop a vertical guide snapped to the left quadrant point of the duplicated&moved circle
create the auxiliary circle by first snapping to the midpoint of the larger circle (for the center), and then - while dragging diagonally downwards with 'Shift' and 'Ctrl' pressed - snapping to the guide just placed (for the radius)

Postby **druban** » Sat Jan 21, 2012 10:18 am

Yes! I understand! .. Although I would just H, ctrl drag the quadrant node of the circle after drawing and snap to the node of the small circle and thereby dispense with the guide, but anyway my question, if indeed I had one! was is there a way to snap a path to path where there is no node on either path?
I can now do this in the latest build

: g3309.png (9.33 KiB) Viewed 11896 times

But with snapping enabled (top button) and ONLY these two options chosen

: rect3391.png (6.46 KiB) Viewed 11896 times

I get no snaps... in other words, no "path to path (tangential)"

chriswww · Postby **chriswww** » Tue Jan 24, 2012 12:13 pm

another way to go towards design/CAD is to create some measure and templating type tools; rather than overloading and overbloating functionality into existing tools. that way you can build some smart features into these non-marking tools, and you use them as guides for inking tools. the inking tools leave marks exactly at guide tool edge. in other words, don't build a pencil that has a ruler and protractor and compass etc., just build these guide tools separately to your marker.

Postby **druban** » Tue Jan 24, 2012 7:38 pm

I think this functionality is already in Inkscape.
Take for example a set of french curves. You can design the exact size and shape of these that you like and put them to the side of your canvas, and then save the file as default. Every time you open a new document these tools will be there. Drag them onto your page to use them.
As far as tracing the edge of a curve or a shape, it's much easier to duplicate the curve, insert a node where you want to begin, another where you want to end, and trim to those nodes. Much quicker than actually following the curve with your pointer. Learnig to use :tool_node:

shortcuts makes it much more useful, joining curves, breaking curves, inverting selection (shortcut: !) and deleting, etc.
You can even put your guide objects in a separate layer and then lock that layer, making it so that you can snap to all your guides, but can't move them or accidentally change their shape.

Also, the measuring tool doesn't get a lot of publicity, but is amazingly versatile, a ruler and protractor in one, measuring without actually having to position it precisely, it snaps to nodes, it can be constrained with ctrl, it ignores locked objects in a smart way, a single pass takes multiple measurements ...

: g3207.png (18.2 KiB) Viewed 11830 times

It does not yet tell you when a measuring line is perpendicular or tangential in the way that other drawing tools have just started doing, but i imagine that will be coming soon. :idea:

(Bonus: The measure tool's control bar is the only place that I have found where you can change the font size used for all the snap annotations!)

Not trying to disparage your request, but I'm just pointing out that Inkscape is capable of very fine drafting work.

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