Calibration¶

Calibration teaches the driver its motor: it checks the magnet and the supply, measures the motor's phase resistance and inductance and computes the current loop gains from them, spins the motor in open loop to find the pole pairs and the direction, checks the order of the phases and aligns the encoder to the rotor field, and measures the motor constants Kt, KV and the flux linkage. Nothing about the motor has to be entered first. It runs once per motor; the result is kept by saving.

The motor turns

Calibration spins the motor in both directions, fast at times. Fix the motor to the bench and take everything off the shaft.

Supply voltage

Calibrate at 24 V. At a lower voltage the resistance, the inductance, KV and Kt come out wrong.

The settings¶

The routine uses six settings, which it prints when it starts. The defaults suit motors with a phase resistance of 2 to 24 Ω; change them only for a motor outside that range.

Setting	Default	Command	What it does
Current loop bandwidth	500 Hz	`#Cbw`	the bandwidth the current loop gains are computed for; too high makes the motor vibrate and whine
Resistance voltage	1000 mV	`#Resv`	the voltage the resistance measurement starts at; it rises until the power reaches the limit below
Max power dissipation	12 W	`#Calpwr`	the power the resistance and inductance measurements may put into the motor
Open loop voltage	5000 mV	`#Openv`	the voltage of the open-loop spin that finds the pole pairs
Open loop speed	20 rad/s	`#Opens`	the electrical speed of that spin
Phase search voltage	5000 mV	`#Vp`	the voltage of the spin that checks the phase order

A seventh setting is not printed: #Iqoffset, 300 mA by default, the current of the angle-offset search and of the commutation check. None of the seven is saved; after a power cycle they are back at these defaults.

Low-resistance motors

These voltages are made for motors of 2 Ω and more. On a motor with a much lower resistance, such as a drone motor, they drive a destructive current. The Spectral Micro is not made for such motors; if you must try one, lower the three voltages first. Lowering the current limit does not help: calibration sets its own.

Calibration sets its own current limit

The routine does not use the current limit you set. It raises the limit to 1600 mA, drives the motor with up to 1250 mA while it measures Kt and KV and with #Iqoffset while it aligns the encoder, and leaves the limit at 1600 mA when it ends. Set the current limit for your motor after calibration and before you save (step 3).

1. Restore the defaults¶

The EEPROM of a new driver, or of one that ran another motor, can hold values that do not fit: another motor's parameters, or junk that shows as -1 in #Info. Calibration starts from what is there, so start from the factory values.

Motor GUITerminal

Default in the settings.

#Default

This also sets the CAN node ID back to 0 and the hardware version and batch date to factory values; note what #Info printed if you need them. Saving the configuration says what else it does.

2. Run it¶

Motor GUITerminal

Start the calibration. The driver enters Calibration mode and the GUI shows its log step by step; when it finishes, the resistance, inductance and pole pairs it measured, the phase order and direction, Kt, KV and the flux linkage appear in the settings.

#Cal

The LED flashes fast, about 10 times a second, while the routine runs, and the driver prints each step as it goes. The numbers below are those of one tested motor; yours will differ:

----------------
Calibration mode
-----Settings-----
Current loop bandwidth: 500.00Hz
Resistance voltage: 1000mV
Max Power dissipation: 12.00W
Open loop voltage: 5000mV
Open loop Speed: 20.00Rad/s
Phase search voltage: 5000mV
----------------
Magnet test: Passed
Vbus test: Passed
Resistance = 7.026575Ohm
Inductance = 0.001492H
Kp_iq = ...
Ki_iq = ...
Pole pair = 11
Dir = 1
Calibrating angle offset... stage 1/13, sweep point 0
Calibrating angle offset... stage 2/13, sweep point 0
...
Phase order = 2
Phase order is good!
KV is: ...
Kt is: ...
Flux linkage is: ...
----------------
Calibration success!
Save config with #Save
Going to idle!
----------------

The Calibrating angle offset... lines come every half second while the encoder is aligned, which can take about 40 seconds; the routine has not stopped.

What the steps are:

Step	What happens	Fails with
Magnet test	the encoder sees enough field: a magnet is there and close enough. The test says nothing about centring, the gap or the glue	`Magnet test: Failed`: magnet missing, too far, or axially magnetised
Vbus test	the supply is within limits	`Vbus test: Failed`
Resistance	a rising voltage is put on the windings and the current measured; the motor clicks. The resistance follows from the two	`Resistance test: Failed`: no current flows, a phase is not connected, or the motor is far outside the 2 to 24 Ω range
Inductance	a voltage step and the rate at which the current rises give the inductance. Kp_iq and Ki_iq are computed from R, L and the bandwidth	`Inductance test: Failed`
Open loop	the stator field is turned at the open-loop speed and the encoder watched: the pole pairs are the ratio of electrical to mechanical turns, and the direction the rotor turned is remembered as `Dir`	`Open loop: Failed`: the encoder saw no rotation
Phase order	a current command must move the rotor the expected way, and the encoder's zero is aligned to the rotor field (the angle offset, `#Offset`). A motor that does not respond gets a second try at another angle	`Commutation/alignment check failed!`, `Motor did not respond as expected to a current command...` and a line `Spin-confirm delta: … ticks (need > 8192), Vbus: … mV` that says how far the motor turned (half a revolution is needed) and at what voltage
Kt, KV, flux linkage	the motor spins fast for a moment and the constants are computed from the back-EMF	—

The measured values are estimates

The resistance, the inductance and the motor constants differ a little from one run to the next, and KV, and with it Kt and the flux linkage, can be off by a factor of two or three on cheap motors with uneven windings. For the loops this does not matter; for a torque estimate in newton-metres, measure Kt yourself.

3. Set the current limit and save¶

Calibration left the current limit at 1600 mA. Set it for your motor first (Current limit and loop tuning), then save, or the 1600 mA are saved with the calibration.

Motor GUITerminal

Set the current limit in the limits, then Save. The GUI marks Unsaved changes until you do.

#Ilim 1000
#Save

Without it the calibration is gone at the next power cycle. The driver goes to idle and the LED shows normal operation; #Info shows Calibrated, the pole pairs, the resistance and inductance, Kt and KV, the phase order and the commutation direction.

Check

After a power cycle #Info still prints Calibrated, and Motor GUI shows Calibrated. Not calibrated means the save did not happen: calibrate and save again.

When to calibrate again¶

After changing the motor, the magnet or the wiring.
After restoring the defaults.
After a firmware update that clears the calibration (a release note says so when it does).

A calibration that reports success but a motor that runs badly afterwards usually means the magnet moved on the shaft between calibration and use: fix the magnet and calibrate again.

Troubleshooting¶

Message	Cause
`Magnet test: Failed`	no magnet, magnet too far (more than about 1.5 mm), or an axially magnetised magnet
`Vbus test: Failed`	supply off, too low, or the cable the wrong way round (if the driver survived it)
`Resistance test: Failed`, `Inductance test: Failed`	a phase not connected or shorted; a motor far outside the 2 to 24 Ω range
the motor wobbles left and right and the routine fails	one phase is not connected
`Open loop: Failed`	the motor did not turn: a phase open, the open-loop voltage (`#Openv`) too low for a high-resistance motor, the supply's current limit set too low
`Commutation/alignment check failed!`	the motor did not respond to the current command: a phase open, `#Iqoffset` set too low, a magnet that slips. Run `#Cal` again. Firmware 101 printed `Phase order is wrong! Switch motor phases and try again!` here; since 105 the wiring is compensated and swapping wires does not help
the routine stops in a step and prints nothing more	reset the driver (`#Reset`) and try again
success, but the LED stays on and no error is reported	`#Info` shows `-1` somewhere: the EEPROM holds a value from an older release (The check at power-up); restore the defaults and calibrate again
the resistance, KV or Kt look wrong	the supply was not 24 V, or the motor is one of the uneven ones; see the note above

Calibration runs over the serial connection only: a terminal, or Motor GUI over the serial adapter, not over CAN.

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