Gimbal Stabilisation

The gimbal controller used in this project is the BaseCam Electronics 32-bit three-axis brushless control board with a frame and main IMU. The frame IMU is on board the controller itself, which is mounted on the gimbal, below-yaw (as sown in the figure below). The main IMU is mounted on the pitch axis where it is subject to all three axes’ movements (also sown in the figure below). These IMUs send real-time feedback to the gimbal controller about the orientation of the surface they are mounted on, relative to their calibration orientations. This type of closed-loop feedback is used to implement Proportional, Integral, Derivative (PID) control algorithms which correct for any errors between the target angle and the current angle of the payload. The gimbal controller is power by a 12 volt 3 cell lithium-polymer battery and in turn powers all the other electronics in the system. The PID algorithm is developed by BaseCam electronics, but the PID values are user-dened, depending on the gimbal properties such as weight, size and motor size. The PID calibration process requires some knowledge of PID controllers and the aects that each term has on the control of the gimbal. Each axis’ gimbal motor is tuned independently as to avoid interference from noise of the un-tuned motors.

Gimbal assembly with component labels
Gimbal assembly with component labels

The derivative control acts like a holding brake on the gimbal motors, minimising overshoot. Too high D-value results in high frequency oscillations of the gimbal motor as it tries to correct for overshoot. The Proportional value adds gain to the motor power, which provides torque to correct the error in the motors target angle and its current angle. Too high P-value results in low frequency oscillations of the motor. The Integral value denes the rate at which the motor corrects for an
error, too high I-value could result in low frequency oscillations and overshoot of the target angle. The PID values were iteratively tuned in the order of derivative, proportional and then integral control until eective stabilisation was achieved.

The video below shows the stabilisation characteristics of the gimbal and how effective it is at keeping the payload level.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s