Ground-based robots are still a nascent thing. Boston Dynamics (robot company) has been building ground-based military robots for a while and they still have problems with them
Kyle Olson, a spokesman for the US marine corps’ Warfighting Lab, explained the problem to Military.com: “As marines were using it, there was the challenge of seeing the potential possibility because of the limitations of the robot itself. They took it as it was: a loud robot that’s going to give away their position.”
The problem there was noise. You can build a much quieter battery-only model... but that impacts its ability to carry loads and range. From what I have seen of the machine itself, terrain wasn't an issue. And these machines are very complex.
Israel has some ground drones they actively use, but they are very expensive
A vehicle alone costs approximately $600,000. With the operating system, the price runs to several million dollars, depending on what equipment is installed on the robot.
Ground robots have to contend with both terrain and enemy action (taking fire, land mines, etc.). They are also no faster than any land vehicle. Given their cost, nobody is using them on a wide scale.
Drones are simpler, and thus easier
What is making drones a far more effective 21st century warfare tool is
- They're much quieter
- They're much smaller (much harder to spot on radar)
- They're cheaper to make
- They can be expendable
- There's not as much in the way of defending against them
Mind you, I'm not talking about a $30M MQ9 Reaper, I'm talking much simpler drones. I mean, you can now build flying bombs that can reach hundreds of miles
Drones have reached the Moscow region, which is about 450km (280 miles) from the border with Ukraine.
This lets you attack targets on the cheap. Ukraine definitely hit on something there
The strike set at least two military planes on fire, and a satellite image taken of Pskov Airport after the incident shows two aircraft completely destroyed.