Hello there!
Sorry for the delay in getting back to you with feedback.
I think the best way to give the character more volume is to create stronger contrast between the light and shadow areas.
Doing this automatically makes the character appear more three-dimensional and solid.
Hope this helps!
Fosco gave you great notes on the shading just wanted to add a bit about volume and wieght. Keep going cool piece love futuristic wateland robot legs | Artwod Feedback