FRAME diffrences

Mogway28 · November 15, 2019, 9:32am

Hello Everyone,
wonder What is the difference between frames OCTA-QUAD V and OCTA-QUAD X.
Is there is different stabilisation, EKF algorithms or it’s just semantics?

Mogway28 · December 7, 2019, 9:57pm

Anyone have some experience ?

iampete · December 7, 2019, 10:29pm

The motor mixers are slightly different to account for the different spacing of rear motors as in the diagrams.
https://ardupilot.org/copter/docs/connect-escs-and-motors.html#octoquad

Mogway28 · December 8, 2019, 7:49pm

OK maybe I should clarify my question . How big those differences are - in many X frames- axes are not 90deg. between arms . Sometimes is >< or V/\ . How to dermine that frame should be OCTO X or OCTO V is better fits. Maybe OCTO V was created for different angle beetween two front and separetly two rear arms ?

iampete · December 8, 2019, 10:50pm

The angle between the arms does not really matter, it matters if the motors are on some rectangle (X or H) or a trapezoid (V). Realistically I doubt that you would notice the difference in mixer unless you had a quite tight tune.

This is the X mixer

github.com

ArduPilot/ardupilot/blob/e4febaf6e05210d134d8408357ff5dbb08a02e4b/libraries/AP_Motors/AP_MotorsMatrix.cpp#L506


switch (frame_class) {


    case MOTOR_FRAME_QUAD:
        switch (frame_type) {
            case MOTOR_FRAME_TYPE_PLUS:
                add_motor(AP_MOTORS_MOT_1,  90, AP_MOTORS_MATRIX_YAW_FACTOR_CCW, 2);
                add_motor(AP_MOTORS_MOT_2, -90, AP_MOTORS_MATRIX_YAW_FACTOR_CCW, 4);
                add_motor(AP_MOTORS_MOT_3,   0, AP_MOTORS_MATRIX_YAW_FACTOR_CW,  1);
                add_motor(AP_MOTORS_MOT_4, 180, AP_MOTORS_MATRIX_YAW_FACTOR_CW,  3);
                break;
            case MOTOR_FRAME_TYPE_X:
                add_motor(AP_MOTORS_MOT_1,   45, AP_MOTORS_MATRIX_YAW_FACTOR_CCW, 1);
                add_motor(AP_MOTORS_MOT_2, -135, AP_MOTORS_MATRIX_YAW_FACTOR_CCW, 3);
                add_motor(AP_MOTORS_MOT_3,  -45, AP_MOTORS_MATRIX_YAW_FACTOR_CW,  4);
                add_motor(AP_MOTORS_MOT_4,  135, AP_MOTORS_MATRIX_YAW_FACTOR_CW,  2);
                break;
            case MOTOR_FRAME_TYPE_BF_X:
                // betaflight quad X order
                // see: https://fpvfrenzy.com/betaflight-motor-order/
                add_motor(AP_MOTORS_MOT_1,  135, AP_MOTORS_MATRIX_YAW_FACTOR_CW, 2);
                add_motor(AP_MOTORS_MOT_2,   45, AP_MOTORS_MATRIX_YAW_FACTOR_CCW,1);

and this is the V

github.com

ArduPilot/ardupilot/blob/e4febaf6e05210d134d8408357ff5dbb08a02e4b/libraries/AP_Motors/AP_MotorsMatrix.cpp#L536


    add_motor(AP_MOTORS_MOT_4,  135, AP_MOTORS_MATRIX_YAW_FACTOR_CW,  2);
    break;
case MOTOR_FRAME_TYPE_CW_X:
    // "clockwise X" motor order. Motors are ordered clockwise from front right
    // matching test order
    add_motor(AP_MOTORS_MOT_1,   45, AP_MOTORS_MATRIX_YAW_FACTOR_CCW, 1);
    add_motor(AP_MOTORS_MOT_2,  135, AP_MOTORS_MATRIX_YAW_FACTOR_CW,  2);
    add_motor(AP_MOTORS_MOT_3, -135, AP_MOTORS_MATRIX_YAW_FACTOR_CCW, 3);
    add_motor(AP_MOTORS_MOT_4,  -45, AP_MOTORS_MATRIX_YAW_FACTOR_CW,  4);
    break;
case MOTOR_FRAME_TYPE_V:
    add_motor(AP_MOTORS_MOT_1,   45,  0.7981f,  1);
    add_motor(AP_MOTORS_MOT_2, -135,  1.0000f,  3);
    add_motor(AP_MOTORS_MOT_3,  -45, -0.7981f,  4);
    add_motor(AP_MOTORS_MOT_4,  135, -1.0000f,  2);
    break;
case MOTOR_FRAME_TYPE_H:
    // H frame set-up - same as X but motors spin in opposite directiSons
    add_motor(AP_MOTORS_MOT_1,   45, AP_MOTORS_MATRIX_YAW_FACTOR_CW,  1);
    add_motor(AP_MOTORS_MOT_2, -135, AP_MOTORS_MATRIX_YAW_FACTOR_CW,  3);
    add_motor(AP_MOTORS_MOT_3,  -45, AP_MOTORS_MATRIX_YAW_FACTOR_CCW, 4);

The only difference is the change from 1 to 0.78981 for the front motors scaling, this is because the front motors are assumed to be further from the CG than the rears.

Mogway28 · December 16, 2019, 1:11pm

Thank You very much for clarification.
Have a nice day.