Section outline

  • Calculating Payload and Limits

    Before putting your robotic arm into action, it is critical to understand its physical limits. Payload refers to the maximum weight the arm can carry without compromising stability or motor performance. Exceeding the payload can damage the servo motors, affect accuracy, or even cause the arm to collapse.

    • Understanding Payload

      Payload is usually specified in grams or kilograms and depends on several factors:

      • Torque of the servo motors used in each joint.
      • Length of the arm segments (longer arms increase leverage and reduce lifting capacity).
      • Weight of the arm itself (a heavy arm consumes more of the available torque).
      • Distribution of weight and center of gravity.

      Torque Basics

      Torque is the turning force a motor can apply, usually given in kg-cm (kilogram-centimeter). For example, a servo rated at 10 kg-cm can theoretically lift a 1 kg load located 10 cm away from the pivot. However, this assumes ideal conditions and no friction or dynamic movement.

      When stacking servos, always remember the base servos must support the weight of everything above — arm segments, attached servos, and the payload.

    • How to Calculate

      Here is a simplified method to check if your robotic arm can lift a load:

      1. Measure the distance (r) from the pivot point to the payload in cm.
      2. Multiply the weight (m) of the payload in kg by gravitational acceleration (g = 9.8 m/s²).
      3. Convert this force to torque: Torque (T) = m × g × r.

      Compare the resulting torque to your servo's rated maximum torque. Add a safety margin of at least 30% to account for dynamic forces and sudden movements.

      Practical Example

      Say you want to lift a 200g load placed 15 cm from the servo:

      • Convert mass to kg: 0.2 kg
      • Torque = 0.2 × 9.8 × 15 = 29.4 kg-cm
      • You would need a servo with at least 35–40 kg-cm torque at that joint.

      Overload Symptoms

      If your robotic arm tries to lift more than it should:

      • Servos may make a buzzing sound without moving.
      • Motion may become jerky or slow.
      • Servos can overheat or shut down to protect themselves.
      • The arm may sag or fail to hold position.

      Tips for Safe Load Handling

      • Use high-torque servos for the base joints.
      • Keep payloads close to the center — reduce arm reach when lifting heavier items.
      • Balance the arm with counterweights if needed.
      • Test each movement before going full speed.

      Proper payload calculation ensures your robotic arm performs reliably and lasts longer. Always test limits gradually and upgrade your hardware if needed for more advanced applications.