Start with the joint package
The single largest mechanical risk on a robotic arm is joint packaging. Motor, gearbox, bearing, encoder, brake, and wiring all have to co-exist inside a structure that is still stiff and light. We size these stacks before we fuss over link shape.
Stiffness decides repeatability
Flex at joints and in long links directly hurts repeatability. That's why we study structural stiffness as a primary objective, not a validation afterthought. A little extra mass near the base is almost always a better trade than a flexible mid-arm.
Design for service, not just assembly
Prototype arms get re-opened constantly. Fastener access, cable routing, and removable covers directly affect how fast you can iterate. Ignoring service cost compounds every time the team has to open the arm in week 3.