<a href="https://en.wikipedia.org/wiki/Four-bar_linkage" class="extiw" title="w:Four-bar linkage">Four-bar linkage</a>:
<ul><li>red: speed vectors</li>
<li>yellow dot: <a href="https://en.wikipedia.org/wiki/Instant_centre_of_rotation" class="extiw" title="w:Instant centre of rotation">Instant centre of rotation</a></li></ul>
<a href="//commons.wikimedia.org/wiki/User:Jahobr" title="User:Jahobr">Jahobr</a>
<span class="int-own-work" lang="en">Own work</span>