You need to consider also possible issues and maintenance. Wheel issues (typical): 1) flat tire (if the wheel is not "solid" only) 2) axle bearing Controlle

You need to consider also possible issues and maintenance. Wheel issues (typical): 1) flat tire (if the wheel is not "solid" only) 2) axle bearing Controller+swinging counterweight: 1) a gazillion electronic components, connectors and contacts, bearings as well, the actuator for the swinging, etc., etc. What happens if the environment is a bit humid? For the wheel, a little rust, for the complex electronic system? And BTW, we can save 25% by using only three wheels ...