Gimbals
Pan_Tilt_Tiger

Gimbals are not just motors with hinges. Modern gimbals have an internal computing unit, motion sensors, and a wealth of knowledge in complex and integrated electromechanics. Gimbals must meet a wide range of operating and performance requirements, such as:

  • Vibrations, shocks and extreme environmental conditions.
  • Immediate and accurate movement.
  • Stabilized movement according to a wide range of sensor types like: MEMS, FOG and GPS.

The gimbal is a motion control system that includes:

  • Motors.
  • Transmission.
  • External sensors like position, temperature and humidity sensors.
  • A control unit that integrates all the system components.
    Each gimbal offers different advantages and disadvantages in terms of size, cost and performance.

Because there are multiple demands from gimbal systems, not all requirements can be adequately addressed in one type of gimbal, so each motion control system has its advantages and disadvantages. Some of the gimbals types are:

  • Direct-Drive: Direct drive motors have many advantages like: immediate response, motion smoothness, high pointing accuracy and error correction. But, the motor current consumption is high, it provides less torque than systems with transmission, and self-locking capability in a non-current state does not exist. Direct-drive motors also tend to be significantly larger and expensive than transmission-driven motors.
  • Belt / Chain Drive: The belt or chain is a transmission-reduction system designed for a small, non-continuous movement. This is a cheap and lightweight solution that improves the flexibility of the system in cases of great winds or inertia, but reduces overall system performance in response to elasticity, so it can not be suitable for precise, independently controlled systems. However, if the parameters of the belt are selected to maintain a high safety coefficient against the maximum load weight in the system, the belts may be very reliable.
  • Helical Transmission Drive: Highly robust and rigid spiral drive systems can be compacted and provide a rigid link between the motor shaft and the load.
    Helical transmission delivers a smooth movement with an instant stopping capability, torque retention even on power off, but transmission efficiency is very problematic because ~50% of the input torque is 'wasted' in self-locking friction.
  • Gear Drive: Transmission gear is divided into two types:
    • Spur Transmission: Based on wheel against a wheel mechanism so that the movement can move from a large multiplication of the tooth and make very gentle and very slow movements (especially for long observation camera applications). A major drawback is that the torque that can be transferred. The torque will always be significantly smaller than the physical size. 

    • Planetary Transmission: A planetary gear (also known as epicyclic gear) consists of two gears mounted so that the center of one gear revolves around the center of the other. A carrier connects the centers of the two gears and rotates to carry one gear, called the planet gear, around the other, called the sun gear. A contact between the the sun and planets teeth transmits the movement so that the motion transition can have a significant torque on the load side. The ratio between its size to transmission ratio is very worthwhile. A major drawback is the freedom between the teeth. While changing the motion direction from CW to CCW (and vice versa), there is an uncontrolled movement of the transmission. This movement is between the direction of the motor and the direction of the load movement, so that inaccuracy is always obtained.

The types of motors that can be used in a gimbal includes Stepper motors and Servo motors.

Stepper motors offer the advantages of high acceleration, torque retention without using a brake or other mechanism. Stepper motors can also be controlled by 'micro-steps' to provide a smooth motion.
Servo motor is a motor that's designed to work faster, so these motors must have a transmission.