# Early-stage Decisions - 2 direct-drive brushless gimbal motors, one for yaw & one for pitch - Main IMU rigidly mounted on camera cradle - Gimbal controller PCB on fixed top plate - Closed-loop stabilization using IMU feedback - Likely using encoder - Negligible weight difference between non/encoder - "camera-mounted IMU feedback can eliminate the need for high-resolution axis encoders in simpler gimbals" # Notes - Feedback loop answers the question "how will the system know that the motor actually put the camera where we wanted it"; see example control law below $ e(t)=\theta_{desired}-\theta_{measured} $ $ u(t)=K_{P}e(t)+K_{I} \int e(t)dt+K_{D} \frac{de}{dt} $ - Likely have to use 2 different motor models b/c $I_{yaw}\gg I_{pitch}$ - iPower GM 3506 (3x torque as GM 2804) - With AS5048A encoder: $54 / 80.3g - Without AS5048 encoder: $24 / 64g - iPower GM 2804 - With AS5048A encoder: $39 / 51g - Without AS5048A encoder: $24 / 42g - IMU tells you "how is the camera actually orienting/moving" - Encoder tells you "what angular position is the motor rotor itself at?" - Very important to balance the pitch axis: as distance between camera CG and pitch axis increases, allowable unbalanced mass decreases. Aim to have offset distance from pitch axis be <10mm, ideally 5mm - Try to keep pitch moving mass < 150-200g - Gimbal controller & flight computer communication protocols - **UART:** simple digital serial link. Usually contains two wires: TX & RX. Flight computer can send commands back like "pitch to -30" and "yaw to +15", and gimbal controller can send status back. Often the simplest practical option - **CAN** is a more robust digital communications bus. Multiple devices can share the same two-wire bus, and it handles electrical noise and longer wiring better than UART - Motors cannot carry all the structural load. Use dedicated bearings or support shafts where needed, **especially on yaw** - Flexible printed frame can create oscillations difficult to tune out w/ PID control. Keep frame short, stiff, and well-braced