Original Blender 2.81 model, with an IK armature, rigged with separate not triangulated bone-parented objects.
[github repo](https://github.com/capnm/b8TransportRobot)
[Same triangulated model](https://skfb.ly/6MQZY) that also demonstrates how the model get currently broken by the (sketchfab) glTF-Exporter on the Web.
[Same model](https://skfb.ly/6MRnZ) and the [animated model](https://skfb.ly/6MR9T) that was first exported from Blender 2.81 to fbx and then uploaded to sketchfab.