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Downforce and Drag added to vertical forces broadcasting #1829

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d68df08
Downforce and drag added to vertical forces broadcasting
efabiyi Jan 25, 2026
2c478c9
Merge branch 'master' into downforce_calculations
efabiyi May 4, 2026
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37 changes: 25 additions & 12 deletions firmware/quintuna/VC/src/app/vehicle_dynamics/app_torqueDistribution.c
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Original file line number Diff line number Diff line change
Expand Up @@ -11,20 +11,29 @@

static PowerLimitingInputs powerLimitingInputs;

void app_wheelVerticalForces_broadcast(const ImuData *imu_data)
void app_wheelVerticalForces_broadcast(const ImuData *imu_data, TractionControl_Inputs *inputs)
{
float drag_lt_per_wheel = DRAG_PITCH_TERM_VERTICAL_FORCE(inputs->vehicle_velocity_kmh) / 2.0f;
app_canTx_VC_FrontLeftWheelVerticalForce_set(
(uint32_t)(((REAR_WEIGHT_DISTRIBUTION - LONG_ACCEL_TERM_VERTICAL_FORCE(imu_data->long_accel)) / 4.0f) -
LAT_ACCEL_TERM_VERTICAL_FORCE(imu_data->lat_accel)));
(uint32_t)(((FRONT_AXLE_WEIGHT_DISTRIBUTION - LONG_ACCEL_TERM_VERTICAL_FORCE(imu_data->long_accel)) / 2.0f) -
(DOWNFORCE_TERM_VERTICAL_FORCE(inputs->vehicle_velocity_kmh) *
STATIC_COP_FRONT(imu_data->long_accel) * STATIC_COP_LEFT(imu_data->lat_accel)) -
LAT_ACCEL_TERM_VERTICAL_FORCE(imu_data->lat_accel) - drag_lt_per_wheel));
app_canTx_VC_FrontRightWheelVerticalForce_set(
(uint32_t)(((REAR_WEIGHT_DISTRIBUTION - LONG_ACCEL_TERM_VERTICAL_FORCE(imu_data->long_accel)) / 4.0f) +
LAT_ACCEL_TERM_VERTICAL_FORCE(imu_data->lat_accel)));
(uint32_t)(((FRONT_AXLE_WEIGHT_DISTRIBUTION - LONG_ACCEL_TERM_VERTICAL_FORCE(imu_data->long_accel)) / 2.0f) +
(DOWNFORCE_TERM_VERTICAL_FORCE(inputs->vehicle_velocity_kmh) *
STATIC_COP_FRONT(imu_data->long_accel) * STATIC_COP_RIGHT(imu_data->lat_accel)) +
LAT_ACCEL_TERM_VERTICAL_FORCE(imu_data->lat_accel) - drag_lt_per_wheel));
app_canTx_VC_RearLeftWheelVerticalForce_set(
(uint32_t)(((REAR_WEIGHT_DISTRIBUTION + LONG_ACCEL_TERM_VERTICAL_FORCE(imu_data->long_accel)) / 4.0f) -
LAT_ACCEL_TERM_VERTICAL_FORCE(imu_data->lat_accel)));
(uint32_t)(((REAR_AXLE_WEIGHT_DISTRIBUTION + LONG_ACCEL_TERM_VERTICAL_FORCE(imu_data->long_accel)) / 2.0f) -
(DOWNFORCE_TERM_VERTICAL_FORCE(inputs->vehicle_velocity_kmh) *
STATIC_COP_REAR(imu_data->long_accel) * STATIC_COP_LEFT(imu_data->lat_accel)) -
LAT_ACCEL_TERM_VERTICAL_FORCE(imu_data->lat_accel) + drag_lt_per_wheel));
app_canTx_VC_RearRightWheelVerticalForce_set(
(uint32_t)(((REAR_WEIGHT_DISTRIBUTION + LONG_ACCEL_TERM_VERTICAL_FORCE(imu_data->long_accel)) / 4.0f) +
LAT_ACCEL_TERM_VERTICAL_FORCE(imu_data->lat_accel)));
(uint32_t)(((REAR_AXLE_WEIGHT_DISTRIBUTION + LONG_ACCEL_TERM_VERTICAL_FORCE(imu_data->long_accel)) / 2.0f) +
(DOWNFORCE_TERM_VERTICAL_FORCE(inputs->vehicle_velocity_kmh) *
STATIC_COP_REAR(imu_data->long_accel) * STATIC_COP_RIGHT(imu_data->lat_accel)) +
LAT_ACCEL_TERM_VERTICAL_FORCE(imu_data->lat_accel) + drag_lt_per_wheel));
}

float app_loadTransferConstant(const float long_accel)
Expand All @@ -50,14 +59,18 @@ void app_torqueAllocation(TorqueAllocationInputs *inputs, TorqueAllocationOutput
// percentage of max torque of motor not of the car

// potential divisino by 0 if load_transfer_const = -1, not sure what values are expected here but should add safety

float drag_comp = DRAG_COMPENSATION_TORQUE_NM(inputs->vehicle_velocity_kmh);

torqueToMotors->front_left_torque =
(inputs->total_torque_request * inputs->load_transfer_const) / (2 * (inputs->load_transfer_const + 1)) -
(inputs->front_yaw_moment / (2 * F));
(inputs->front_yaw_moment / (2 * F)) + drag_comp;
torqueToMotors->front_right_torque = (torqueToMotors->front_left_torque + (inputs->front_yaw_moment / F));

torqueToMotors->rear_left_torque =
(inputs->total_torque_request / 2) -
(inputs->total_torque_request * inputs->load_transfer_const) / (2 * (inputs->load_transfer_const + 1));
((inputs->total_torque_request / 2) -
(inputs->total_torque_request * inputs->load_transfer_const) / (2 * (inputs->load_transfer_const + 1))) +
drag_comp;
torqueToMotors->rear_right_torque = (torqueToMotors->rear_left_torque + (inputs->rear_yaw_moment / F));

powerLimitingInputs.total_requestedPower = app_totalPower(torqueToMotors);
Expand Down
2 changes: 1 addition & 1 deletion firmware/quintuna/VC/src/app/vehicle_dynamics/app_torqueDistribution.h
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@
* Broadcasts the vertical force of each wheel
* calculated based on IMU accelerations
*/
void app_wheelVerticalForces_broadcast(const ImuData *imu);
void app_wheelVerticalForces_broadcast(const ImuData *imu, TractionControl_Inputs *inputs);

/*
* Calculates the load transfer constant needed to distribute torque
Expand Down
32 changes: 31 additions & 1 deletion firmware/quintuna/VC/src/app/vehicle_dynamics/app_vehicleDynamicsConstants.h
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,15 @@
#define MAX_REGEN_Nm -15.0f
#define MAX_BATTERY_TEMP 45
#define POWER_LIMIT_REGEN_kW 17.0f // 17.64kW ~ 30A charge for molicel cells
#define FRONTAL_AREA 0.94f // m^2 from aero team
#define AIR_DENSITY 1.2205f // kg/m^3
#define COEFFICIENT_OF_LIFT 1.7f // from Aero team
#define COEFFICIENT_OF_DRAG 1.1f // from Aero team
#define COP_REAR 0.68f // from Aero team
#define COP_RIGHT 0.5f // Assumed symmetric. Aero team has not characterized lateral CoP
#define COP_HEIGHT (42.0f * CM_TO_M)
#define WHEEL_RADIUS_m ((WHEEL_DIAMETER_IN / 2.0f) * 0.0254f)
#define KMH_TO_MS (1.0f / 3.6f)

/**
* Reference used: https://www.zotero.org/groups/5809911/vehicle_controls_2024/items/N4TQBR67/reader
Expand All @@ -39,13 +48,34 @@
#define DIST_FRONT_AXLE_CG (0.837f) // a in meters
#define DIST_REAR_AXLE_CG (WHEELBASE_m - DIST_FRONT_AXLE_CG) // b in meters
#define WEIGHT_ACROSS_BODY (CAR_MASS_AT_CG_KG * GRAVITY / WHEELBASE_m)
#define DOWNFORCE_CONSTANT (AIR_DENSITY * FRONTAL_AREA * COEFFICIENT_OF_LIFT / 2.0f)
#define DRAG_CONSTANT (AIR_DENSITY * FRONTAL_AREA * COEFFICIENT_OF_DRAG / 2.0f)

/************** Macros for finding vertical forces on wheels based on diagram on page 21 ****************/
#define REAR_WEIGHT_DISTRIBUTION (WEIGHT_ACROSS_BODY * DIST_REAR_AXLE_CG)
#define FRONT_AXLE_WEIGHT_DISTRIBUTION (WEIGHT_ACROSS_BODY * DIST_REAR_AXLE_CG)
#define REAR_AXLE_WEIGHT_DISTRIBUTION (WEIGHT_ACROSS_BODY * DIST_FRONT_AXLE_CG)
#define LONG_ACCEL_TERM_VERTICAL_FORCE(long_accel) \
((CAR_MASS_AT_CG_KG * (long_accel) * CG_HEIGHT_FROM_GROUND_m / WHEELBASE_m))
#define LAT_ACCEL_TERM_VERTICAL_FORCE(lat_accel) \
((CAR_MASS_AT_CG_KG * (lat_accel) * CG_HEIGHT_FROM_GROUND_m / (2.0f * (TRACK_WIDTH_m))))
#define DOWNFORCE_TERM_VERTICAL_FORCE(vehicle_velocity_kmh) \
((DOWNFORCE_CONSTANT) * (vehicle_velocity_kmh * KMH_TO_MS) * (vehicle_velocity_kmh * KMH_TO_MS))

// Longitudinal CoP shift with pitch not modeled — aero team to provide data next year

#define STATIC_COP_FRONT(long_accel) (1 - (COP_REAR))
#define STATIC_COP_REAR(long_accel) (COP_REAR)
#define STATIC_COP_LEFT(lat_accel) (COP_RIGHT)
#define STATIC_COP_RIGHT(lat_accel) (1 - (COP_RIGHT))

#define DRAG_FORCE_NEWTONS(vehicle_velocity_kmh) \
((DRAG_CONSTANT) * (vehicle_velocity_kmh * KMH_TO_MS) * (vehicle_velocity_kmh * KMH_TO_MS))
#define DRAG_PITCH_TERM_VERTICAL_FORCE(vehicle_velocity_kmh) \
((DRAG_FORCE_NEWTONS(vehicle_velocity_kmh) * COP_HEIGHT / WHEELBASE_m))

// Torque required to counteract resistive drag force per motor (4WD)
#define DRAG_COMPENSATION_TORQUE_NM(vehicle_velocity_kmh) \
((DRAG_FORCE_NEWTONS(vehicle_velocity_kmh) * WHEEL_RADIUS_m) / 4.0f)

/************** Macros for finding Kmz based on diagram on page 57 ****************/
#define ACCELERATION_TERM_KMZ(long_accel) (DIST_FRONT_AXLE_CG + (long_accel) * CG_HEIGHT_FROM_GROUND_m / GRAVITY)
Expand Down
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