How to choose the right material for building a combat robot

Each part of the robot has a different function and requires different material properties.

The chassis is the skeleton of the robot that holds everything together. It must be strong, but at the same time as light as possible so that as much weight as possible can be allocated to the armor and weapon.

• Aluminum alloys (e.g., 6061, 7075): A very popular choice for most weight classes. It offers an excellent strength-to-weight ratio, is easy to machine, and is affordable. Alloy 7075 is significantly stronger than 6061, but also more expensive and more difficult to weld.
• Plastics for 3D printing (PETG, Nylon, Polycarbonate): Dominate the lighter categories (up to 1.5 kg). They allow you to create complex and optimized shapes. PETG is a great beginner material, while Nylon and Polycarbonate (PC) offer extreme impact and crack resistance.
• Polycarbonate (e.g., Lexan): Excellent for its extreme impact resistance. Often used in combination with a metal frame.
• Steel: Used less often due to its high weight, but may be suitable for some specific, very robust designs.

Recommendation: For light weights (up to 3 pounds/1.36 kg), 3D printing from PETG or Nylon is ideal. For heavier categories (15 pounds/6.8 kg and above), machined aluminum 6061 or 7075 is the standard.

The purpose of armor is to withstand enemy attacks. It must be hard enough to resist penetration and tough enough not to crack.

• Abrasion-resistant steel (Hardox, AR500): The gold standard for protection against rotary weapons. It is extremely hard and relatively inexpensive, but very heavy. Ideal for front armor or the most exposed areas.
• Titanium (Grade 5, 6Al-4V): It has about half the density of steel but still has excellent strength. It is a premium material that offers great protection with significant weight savings. Its disadvantages are high cost and difficult machining.
• Aluminum alloy 7075: Can serve as lighter armor, but does not provide sufficient protection against steel weapons. It is more suitable against other aluminum weapons or as an additional layer.
• UHMW-PE (Ultra-High Molecular Weight Polyethylene): A very light plastic that absorbs impact energy very well. Even if a rotary weapon cuts through it, the material does not crack and often “heals” itself with the heat from friction. It is used as side or rear armor where direct hits are not expected.

Recommendation: If weight is your top priority, use titanium. If your budget is limited but you need maximum protection, choose AR500 steel. UHMW-PE is great for less critical parts.

The material of the weapon varies depending on its type.

• Spinning weapons (Spinners):
  • S7 steel: Tool steel that is extremely tough and impact resistant. It is the best choice for spinning weapons that are designed to survive collisions with other steel weapons.
  • AR500 steel: A cheaper alternative to S7. It is harder but more brittle. Good for beginners, but more prone to breaking on impact.
  • Aluminum 7075: Used for very fast spinning weapons in lighter categories, where the goal is to knock the opponent away rather than break them.
• Flippers and Lifters:
  • The most important part is the flipper arm. Aluminum 7075 or steel is often used for maximum stiffness so that energy is transferred to the opponent and not to the bending of the arm.
• Hammers:
  • The hammer head must be made of extremely hard material. Hardened tool steel (S7) or other steel alloys are used.

• Robot “Spinner”: Most of the weight must be concentrated on the weapon and drive. The chassis should be as light as possible (aluminum, 3D printing) and the armor as durable as possible (AR500 steel, titanium) in areas where it is likely to be hit.
• “Flipper” robot or control robot: The weapon is relatively light, so more weight is left for a robust chassis and durable armor. The goal is to survive hits and control opponents. Strong aluminum frames and titanium or UHMW-PE plates are often used here.
• Lightweight categories (up to 3 pounds): 3D-printed plastics (PETG, Nylon) and polycarbonate dominate here. Weight is so critical that metals are used almost exclusively for weapons and motors.
• Heavyweight categories (250 pounds / 113 kg – BattleBots): Here, the standard is a combination of machined 7075 aluminum for the chassis and AR500 steel or titanium plates for armor. Weapons are almost exclusively made of S7 tool steel.

1. Set your budget and weight limit.
2. Decide on the type and strategy of your robot.
3. Perform a “weight balance”: Estimate how much the mandatory components (motors, batteries, electronics) will weigh.
4. Distribute the rest of the weight: Based on your strategy, allocate the remaining weight between the weapon, armor, and chassis.
5. Select specific materials: Considering the allocated weight and function of each part, select the most suitable materials from the list above.