The IIT R1 humanoid project had a tight schedule and needed outside assistance with mechanical design.
We did two separate works for this project. First we created an alternative 2DoF shoulder design that could be used as a fallback if the first approach did not work. This design was eventually used.
Second we did the mechanical design of the 2 wheel base. Challenges included fitting all components within a volume predefined by the industrial designers, and, because motors, batteries, and computers were all sharing the same volume, creating a good thermal flow. The design minimized the part count and used sheet-metal techniques that could be scaled to larger volumes.