I want to draw a circle or circle outline (to represent a pulley), and two vertical lines (to represent a belt around the pulley). Something like this:
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|…|
| O |
I want the top ends of the vertical lines to remain stationary (fixed in place). I want the bottom ends of the vertical lines to end at (at least approximate) tangents to the circle. When I move the center of the circle up and down, I want the vertical lines to shrink or stretch.
At first I tried linking an end of a spline to one vertex of the circle, but that did not make the end of the spline coincide with the vertex of the circle. Instead, the end of the spline got connected to the control handle of the vertex. They move together when I drag the vertex or the handle, but the end of the line is distant from the edge of the circle.
Ultimately, I want to animate the circle, so it moves up and down and the two lines automatically shrink or grow.
I am new to Synfig. Does anyone have a suggestion?
I created a skeleton (bone) with two child bones. I then parented the main bone to the circle and parented each child bone to the lower vertex of the vertical lines. Since the main bone controls the other bones; when it’s moved everything moves with it. Hope this helps if not then I would have to demonstrate how tomorrow as I’m feeling sleepy now
You could also do some alterations with the Dynamic converter (But there’s not much control there:
Thank you. I had not yet learned about bones. They seem very useful for animating character (people, animals, etc.) My interest is more toward educational animation, so I didn’t think that bones would be important to me, but clearly I was wrong. I will read up about bones and follow your instructions. I really appreciate your help. I had been banging my head against this problem for two days!
You could also use Converters for Layer parameters and/or linking/connecting parameters.
If you know French this video could easily help you Synfig tutoriel (animation) : Pendule simple - YouTube
Even if you don’t know, I suppose you can understand it as its interface is in English and he shows equations with english variable names.
Thanks, again. I was able to create my “engineer operating a crane” using bones. Here is a screenshot of it. Being a new user on the forum, I am not yet permitted to upload attachments, otherwise I would have also uploaded a copy of my .sifz file.
By further experimenting, I found I could simplify the drawing to only one bone. I linked the location of the Hook group to the bone, and I linked both bottom vertexes of the Lift cable outline to the same bone. Moving the location vertex of the bone moves the Pulley assembly (with hook) up and down and shrinks or stretches the rectangle that depicts the belt, by which the pulley is suspended.
That is very kind of you to say, but really I am just getting started and have much to learn. Thank you for the various videos you produced. I have found several of them helpful.
I have no drawing talent, so my drawings are limited to crude stick figures, often copied from images on the web. Nevertheless, Synfig seems like a very nice program. It is certainly useful for my instructional videos.
-George
if not then I would have to demonstrate how tomorrow as I’m feeling sleepy now 
