Are Free Will and Motivation related?
To want, to feel, and to think, also known as conation, emotion, and cognition are the three basic categories that psychology is traditionally concerned with. The term conation as far as I know is rather outdated (see Winch, 1909), whereas motivation is the newer term for the "drive to act". 

As usual within psychology, the term "conation" is not used consistently. However, even when motivation and conation are given distinct meanings, the terms are still closely related to each other (e.g. Reitan &amp; Wolfson, 2000).

To sum up, the concept of (free) will is a subcategory of motivation/conation whereas sibling categories are interest or desire. 

References

Reitan, R. M., &amp; Wolfson, D. (2000). Conation: A Neglected Aspect of Neuropsychological Functioning. Archives of Clinical Neuropsychology, 15(5), 443–453. https://doi.org/10.1016/S0887-6177(99)00043-8

Winch, W. H. (1909). Conation and Mental Activity. II. The Journal of Philosophy, Psychology and Scientific Methods, 6(19), 505–514. https://doi.org/10.2307/2012061