MESC_control_variables.md

MESC Motor Control Variables

A listing of variables in the MESC firmware that are particularly relevant to balancing.

🔹 Input & Control Variables

• UART_req

  • Main user input variable.
  • Written from UART commands or CAN handlers (CAN_ID_ADC1_2_REQ, CAN_ID_IQREQ).
  • Passed into MESCinput_Collect() and merged into FOC.Idq_req.q.
  • Typically treated as normalized [-1.0 … +1.0], then scaled by max_request_Idq.q / min_request_Idq.q.

• remote_ADC1_req / remote_ADC2_req

  • Populated from CAN_ID_ADC1_2_REQ packets.
  • Mirror the function of physical ADC throttle inputs but come via CAN.
  • Flow into the same path as throttle inputs.

• remote_Iq_req

  • Intended variable for remote torque/current commands via CAN (CAN_ID_IQREQ).
  • In your firmware branch, this was bypassed and written directly to UART_req instead.
  • Author’s style suggests remote_Iq_req is the canonical variable.

• remote_ADC_timeout / remote_Iq_timeout

  • Countdown timers reset whenever a new CAN packet arrives.
  • If they expire (no packets for a few cycles), input is invalidated → ESC zeros the torque command for safety.

• FOC.Idq_req.q

  • Final q-axis current request (in amps).
  • This is what the inner current control loop actually tries to track.
  • Computed inside the control loop from inputs (UART_req, speed loops, etc.).
  • Should not be written to directly from CAN/UART — it gets overwritten each cycle.

• max_request_Idq.q / min_request_Idq.q

  • Configured current limits (positive/negative).
  • Define the maximum torque the ESC will ever command.
  • All normalized requests (UART_req, remote_ADC) are scaled by these bounds.

• mtr[0]->FOC.enc_angle

  • A 16-bit fixed-point mechanical angle, derived from the encoder timer’s CNT, scaled so that it runs 0–65536 per cycle, and resynchronized by the encoder’s Z-pulse via CCR1.
  • mtr[0]->FOC.enc_angle is calculated as:
  • enc_angle=pole_pairs×enc_ratio×(CNT−CCR3)+offset
  • CNT gives the live position, while CCR3 (index pulse latch) ensures the angle resets to a known reference once per mechanical revolution.
  • CNT → current quadrature count (mechanical position since last Z).
    • → This provides the absolute reference point per revolution.
  • Relative count
    • (CNT - CCR3) → ticks since last Z-index pulse.
  • enc_ratio converts raw encoder ticks → fixed-point [0…65536] mechanical rev.
  • Then multiplied by pole_pairs → converts to magnetic motor position.
  • If encoder_polarity_invert is set, it flips the direction by subtracting from 65536.
  • enc_offset allows calibration of zero-angle alignment (phase alignment between encoder mechanical zero and motor electrical zero).

• mtr[0]->FOC.abs_position

  Created for this project. Notice this code addition:

  #ifdef POSVEL_PLANE
  if(_motor->FOC.encoder_polarity_invert){
      // Invert direction for abs_position as well
      _motor->FOC.abs_position = ((uint16_t)(_motor->enctimer->Instance->CCR3) - (uint16_t)(_motor->enctimer->Instance->CNT)) & 0x0FFF; // 12-bit wrap
  } else {
      _motor->FOC.abs_position = ((uint16_t)(_motor->enctimer->Instance->CNT)  - (uint16_t)(_motor->enctimer->Instance->CCR3)) & 0x0FFF; // 12-bit wrap
  }
  #endif

  • The raw mechanical encoder position (0–4096) adjusted to an absolute reference using the Z-pulse (CCR3)
  • FOC.abs_position → ( (uint16_t)(CNT) - (uint16_t)(CCR3) ) & 0x0FFF; // for 12-bit encoder
  • CNT → current encoder count (0–4095).
  • CCR3 → latched value of CNT when the Z-pulse occurred.
  • (CNT - CCR3) → ticks since the last index (Z-pulse).
  • Note: if it wasnt obvious already 4095 is hardcoded all over the place in MESC.

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Current MESC Settings

Parameter	Value
adc1	640
adc1_max	2700
adc1_min	500
adc1_pol	1.000000
adc2_max	4095
adc2_min	1200
adc2_pol	1.000000
can_adc	3
ehz	-0.283872
error	0
error_all	0
FOC_Advance	0.000000
FOC_angle	40500
FOC_curr_BW	3000.000000
FOC_enc_ang	40500
FOC_enc_oset	40500
FOC_enc_pol	1
FOC_enc_PPR	4096
FOC_flux_gain	0.367423
FOC_flux_gain	0.367423
FOC_flux_nlin	5000.000000
FOC_fpwm	20000.000000
FOC_fw_ehz	0.000000
FOC_hall_array_ok	0
FOC_hall_iir	0.950000
FOC_hall_Vt	2.000000
FOC_hfi_eHz	0.000000
FOC_hfi_type	1
FOC_hfi_volt	1.000000
FOC_Max_Mod	0.950000
FOC_obs_type	1
FOC_ol_step	10
FOC_ortega_gain	1000000.000000
Hall_flux	Array[12]
id	-0.007379
input_opt	32
iq	-0.000819
iqreq	0.000000
meas_cl_curr	8.500000
meas_curr	20.000000
meas_volt	4.000000
node_id	12
opt_app_type	0
opt_circ_lim	2
opt_cont_type	0
opt_fw	2
opt_hall_start	false
opt_lr_obs	false
opt_motor_temp	false
opt_mtpa	0
opt_phase_bal	false
opt_pwm_type	0
par_dir	0
par_flux	0.001350
par_fw_curr	0.000000
par_i_max	50.000000
par_i_min	-50.000000
par_i_park	0.000000
par_ibat_max	10.000000
par_ld	0.000015
par_lq	0.000022
par_motor_sensor	4
par_p_max	3000.000000
par_pp	14
par_r	0.070000
par_rpm_max	0
par_SL_sensor	0
password
safe_count	100
safe_start	100
speed_ki	0.100000
speed_kp	0.500000
speed_req	0.000000
TMOS	299.611572
TMOT	199.968307
uart_dreq	0.000000
uart_req	0.000000
vbus	29.723145
Vd	-0.004284
Vq	0.006748