Other Parts Discussed in Thread: MCF8329RRYEVM, MCF8316A, MOTORSTUDIO
Tool/software:
Other Parts Discussed in Thread: MCF8316A; also MCF8329RRYEVM
Tool/software: MotorStudio
Motor: Maxon ECX SPEED 13 M, 18 V winding: 74.5 krpm, 1.55 A, 3.02 mNm, ŋMax = 85%
sequential goals, under I²C speed control
- Run motor to 70,000 rpm.
- Complete MPET.
- actual objective: Configure [1] MCF8316Ds on custom boards that we have in hand.
How can I get past repeated fault interruptions; apparently by MPET [2],
even when I²C Speed Command = 0%?
- Algorithm State jumps to MOTOR_MPET_KE_MEASURE, spins for ~6 s, then faults: CONTROL + MPET_BEMF.
- After one time power cycling 18 V, about once per second: state alternates between MOTOR_MPET_KE_MEASURE and MOTOR_MPET_MOTOR_BRAKE; faults: DRIVER_FAULT, OCP, and OCP_HA/LA/LB; motor twitches less than a full turn.
Even switching back to speed control from the pot, the motor only twitches at about the same rate.
work flow complication: MotorStudio finds custom JSONs to be invalid for loading.
Why does MPET keep starting even after disabling it in GUI,clearing MPET_CMD, or controlling speed from the pot?
Is there another register to clear, to stop MPET from auto-running after power cycle?
Is there a recommended sequence to:
- Disable MPET completely for I²C speed control?
- Later re-enable MPET and complete Ke measurement without faults?
And while I have your attention, are my brake and open-loop settings reasonable for a 70 k rpm target on this motor?
narrative version
With “Speed Control via I2C ”Enabled; before MPET interrupted consistently
—upon my clearing faults, even when the I2C Speed Command Percentage slider set to zero, the Algorithm State would go to MOTOR_MPET_KE_MEASURE. Rotation would accelerate for six seconds or so; then the motor would stop vibrating and so feel as though it were coasting rather than accelerating. The CONTROL and MPET BEMF faults would latch on, and the motor would no longer sustain rotation.
I introduced the second condition when I cycled the 18 V supply. Now, about once a second, MOTOR_MPET_KE_MEASURE and MOTOR_MPET_MOTOR_BRAKE alternate, three faults appear and clear on their own, and the motor makes an incomplete rotation. The three faults are DRIVER_FAULT, OCP, and OCP_xx. The third of these is sometimes OCP_HA, sometimes OCP_LA instead, and sometimes OCP_LB instead. Otherwise, this l5.+ooks somewhat like [3], which instead was about MCf8329RRYEVM .
Again; even switching back to speed control from the pot, the motor only twitches at about the same rate.
This situation persists even with the following provisions, to disable MPET etc., as follows;
- all Measure toggles: Disable, in the MPET pane of MotorStudio
- MPET_CMD: unchecked, in ALGO_DEBUG2
- BRK_CONFIG: “Brake current threshold and Brake time is used to come out of brake state”
- BRAKE_EN: Enabled
- RVS_DR_EN: Disable
- BRK_MODE: All three low side FETS turned ON, per SLLA663 pre-startup tuning guide
BRK_CURR THR: 0.2 A
BRK_TIME: 500 ms
OL_LIMIT: 1.5 A
Auto Handoff: Enable
OPN_CL_HANDOFF_THR: 20%
OL_ACC_AC1: 100 Hz/s
OL_ACC_AC2: 1 Hz/s
OCP deglitch: 1.6 µs
MTR_STOP: Recirculation Stop
ALGORITHM_STATE: 0x11 or 0x14
[2] Like Taylor Sullivan-Peters, last month
Also like T. S.-P., we in-shop have our previous experience with an MCF8316A; e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1407331/mcf8316aevm-startup-issues-in-firmware
attachments: Word file with register map (and JSON values from MotorStudio, after first a spin using EVM onboard pot for speed control, and then MPET)
and intended settings on the right, superseded by the provisions I listed above
Wdh005ø tuning parameters.docx
motor datasheet excerpt for 18 V winding
ECX SPEED 13 M, ∅13 mm BLDC; 1 pole pair, 3 phases
25/27 W, 3.6 mNm, 120 000 rpm max
Nominal voltage: 18 V
No load speed: 77, 600 rpm
No load current: 186 mA
Nominal speed: 73, 900 rpm
Nominal torque (max. continuous): 0.00302 N·m
Nominal current (max. continuous): 1.55 A
→ OL_ILIMIT←1.5 A
→ IPD current starting ←0.75 A
Stall torque: 0.0688 N·m
Stall current: 31.3 A
Max. efficiency: 85 % → IPD Current Threshold←0.75 A
Terminal resistance: → OCP & LOCK_ILIMIT safety margins
Terminal inductance: 0.0135 mH
Torque constant (Kt): 0.00220 N·m/A
Speed constant (Kv): 4340 rpm/V; taking Ke ≈ 1/Kv ≈ 0.158 V/(rad/s) → ≈ 2.53 mV/Hz
Speed/torque gradient: 1140 rpm/mNm
Mechanical time constant: 1.55 ms
Rotor inertia: 0.13 g·cm²
________________________________________
Thermal resistance, housing- ambient: 29.5 K/W
Thermal resistance, winding- housing: 2.5 K/W
Thermal time constant, winding: 1.69 s
Thermal time constant, motor: 475 s
Ambient temperature range: –40 … +135 °C
Max. winding temperature: 155 °C
