I'm writing this article to share how I will go through my thinking process if I were to design fighting robots.
It's always good to list down your design specs, the guidelines (usually set by your art directors or clients).
Usually before I went into creating silhouettes for my robots, I will brainstorm or construct a mind map on how my robots will function. Attached are two charts or simple keywords that I can think of. I will list them down and feel free to mix and match the elements to suit to my design specs.
It is my preference that I kinda know what I'm heading towards, so that I am more confident on the task and it helps me to see shapes, derives object that make sense from plain silhouettes.
Its always good to keep an open mind about possibilities. For example; Earthburrow robots that can teleport? How about mixing more than 2 elements? Mechanical birds type that swim? Robot penguins? It is advisable to do research on how things move. Chains, pulley system, hydraulics and etc. Usually just these 2 list can create almost unlimited amount of ideas. Let's look at the next chart.
Over here, I focus on lists that might give me ideas on the level 2 and 3 details (look wise) and how your robots attacks and possible weakness. Being a fighting robot, its going to be able to deal damages and also defend from attacks. How long can it attack and how can it detect it's foe.
The coolest thing is nature. Not only we can derive silhouettes from nature but also on how she works. How does the snakes detect prey? Smell, taste and even heat. What about vibration or even something simple like an eye that can detect any light spectrum (Eg; Predator).
Chameleons and octopus sometimes changes their skin color to blend into environment. This gives them the ability to avoid detection. Stealth planes are made with special material and shapes to make their radar visibility on enemies reduce to the minimal.
Now to the fun part. How does your robots fight? Well, we have the conventional way. Projectiles + Heat = Explosion. Most of our modern weapon belongs to this type. Using the chart above, what about chemical. Robots that throws acids? What other way we can use heat? What if the robot has a pincer that has a high heat strips inside and it melts the foe as it grabs. Just by cutting, we can have drills and slash. Punch or crush or it can propel (like a magnet) the foe to a wall to deal damage. They say that time, is the greatest destroyer or all things. Maybe the robot can throw the opponent into a time portal that causes the foe to deteriorate (rust, disintegrate) at a speed of 1000x faster than normal space time.
Usually I prefer to go for functions then the look. But its equally important. You do not want to have a walking water bottle that holds a knife. The above process, if you get it right, it helps you to generate silhouettes and simply anything can mean something to you. The most common problem people faces are when they have no idea what qualities their robots have.
Hope these help. Feel free to design your robots and if you like, can show it to me too!