As planned I've used previously showen arms as a base mesh to create high poly and low poly versions of the mechanical arms. To create high poly version I had to separate arms parts in to 25 subtools for more comfortable work with high subdivision levels individually on each subtool. I've made all surfaces look polished and smooth after that I've added all the fine details like bolts, screws and scratches.

 Low poly version was done next. To make it I've made new topology of the shoulder, fingers and forearm parts everything else remained same polygon density as it was on base mesh. By changing this parts topology I've created much lower polygon count and simplified geometry details. I've used move brush to tweak low poly surface and move it so that it is slightly higher than high poly mesh surface to avoid overlapping this will prevent me from errors of normal map baking in the future.