Nunchuk application

Use a Wii Nunchuk controller over I2C to control the motor with the joystick and buttons.

The Nunchuk application reads data from a standard Wii Nunchuk controller connected over I2C. The joystick Y-axis controls the motor output level while the C and Z buttons provide secondary functions such as braking, cruise control, and reverse.

Hardware connection

The Nunchuk uses the I2C bus on the VESC. Wire it to the I2C pins on your hardware’s expansion header:

Nunchuk wire	VESC signal
White (SCL)	I2C clock
Green (SDA)	I2C data
Red (3.3 V)	3.3 V supply
Yellow (GND)	Ground

Original Nintendo Nunchuk controllers and most aftermarket clones work with this application. The firmware communicates over I2C at the standard Nunchuk address 0x52.

Control types

typedef enum {
    CHUK_CTRL_TYPE_NONE = 0,
    CHUK_CTRL_TYPE_CURRENT,
    CHUK_CTRL_TYPE_CURRENT_NOREV,
    CHUK_CTRL_TYPE_CURRENT_BIDIRECTIONAL
} chuk_control_type;

Type	Description
CURRENT	Current control. Smart reverse available via Z button hold.
CURRENT_NOREV	Current control, forward only.
CURRENT_BIDIRECTIONAL	Full bidirectional current control without smart reverse.

Button functions

The Nunchuk has two buttons, C (upper) and Z (lower trigger):

Button	Function
Z	Braking when pressed while rolling. Hold from idle to activate smart reverse.
C	Cruise control — locks the current output level when pressed.

Button state is exposed through the runtime API:

bool app_nunchuk_get_bt_c(void);   // C button state
bool app_nunchuk_get_bt_z(void);   // Z button state
bool app_nunchuk_get_is_rev(void); // Currently in reverse

Configuration struct

typedef struct {
    chuk_control_type ctrl_type;
    float hyst;
    float ramp_time_pos;
    float ramp_time_neg;
    float stick_erpm_per_s_in_cc;
    float throttle_exp;
    float throttle_exp_brake;
    thr_exp_mode throttle_exp_mode;
    bool multi_esc;
    bool tc;
    float tc_max_diff;
    bool use_smart_rev;
    float smart_rev_max_duty;
    float smart_rev_ramp_time;
} chuk_config;

Key parameters

Field	Default	Description
hyst	0.15	Joystick deadband around center.
ramp_time_pos	0.4 s	Positive output ramp time.
ramp_time_neg	0.2 s	Negative output ramp time.
stick_erpm_per_s_in_cc	3000 ERPM/s	Speed change rate when adjusting cruise control with the joystick.
use_smart_rev	true	Enables timed smart-reverse on Z button hold.
smart_rev_max_duty	0.07	Maximum duty during smart reverse.
smart_rev_ramp_time	3.0 s	Time Z must be held to enter smart reverse.
multi_esc	true	Forwards command to CAN-connected VESCs.
tc	false	Traction control between paired ESCs.

Timeout

If no I2C data is received within LOCAL_TIMEOUT (2000 ms, defined in app_nunchuk.c), the output is cut. This protects against a disconnected cable during operation.

Runtime API

void app_nunchuk_start(void);
void app_nunchuk_stop(void);
void app_nunchuk_configure(chuk_config *conf);
float app_nunchuk_get_decoded_x(void);   // Joystick X-axis (−1 to 1)
float app_nunchuk_get_decoded_y(void);   // Joystick Y-axis (−1 to 1)
bool  app_nunchuk_get_bt_c(void);
bool  app_nunchuk_get_bt_z(void);
bool  app_nunchuk_get_is_rev(void);
float app_nunchuk_get_update_age(void);  // Seconds since last update
void  app_nunchuk_update_output(chuck_data *data);