I am going to order my Banebots parts soon and I was wondering what I should get in the way of spares.

I was going to get 4 motors and 3 gearbox's but I just wonder if I should get 4 of each so I have a total replacement set.

Has anyone ever had on of their gearbox's fail through general combat? I mean getting smacked by NST on the shaft will obviously break it but what experience have people got with them?

Oh and does anyone have an accurate density for Hardox 400? Ellis and i have been looking and it can swing from 7650kg/m^3 to 9345kg/m^3.