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Tercio S1

Encoders

3 min readFirmware v2 · protocol v2

The S1 closes its loop on one of three magnetic encoders: the AS5600 under the board, or an AS5600 or AS5048A on the 12-pin connector.

Choosing an encoder

Section titled “Choosing an encoder”
12 bits · 0.088°
AS5600, on boardUnder the S1, on the motor’s magnet. The default. Setting: On-board AS5600.
12 bits · 0.088°
AS5600, externalI²C on J2. For an encoder elsewhere, such as an output shaft. Setting: External AS5600 (I²C).
14 bits · 0.022°
AS5048A, externalSPI on J2. Four times the resolution, and a longer cable run. Setting: External AS5048A (SPI).

Every encoder is absolute within one turn. The AS5600 is read about 13,000 times a second (twice as often as it measures), the AS5048A on every 50 µs pass of the loop. The S1 counts whole turns itself and estimates speed between readings.

Wiring for the external ones is in Wiring → External encoder.

Changing the encoder

Section titled “Changing the encoder”
  1. Disable the motor. The Encoder setting can only change while disabled.
  2. Under Settings → Encoder, choose the encoder and Apply.
  3. Changing the encoder clears the calibration and the zero: they belong to the old sensor.
  4. Run Calibrate again, then Save to motor.

If the new encoder cannot be read, the S1 raises the Encoder fault. Check the wiring and the magnet, then Clear faults.

Gearboxes

Section titled “Gearboxes”

With the encoder on the output of a gearbox, the S1 controls the output shaft:

  • Set Gear ratio to motor turns per output turn, for example 5 for a 5:1 gearbox.
  • Positions, speeds and limits are then in output turns.
  • Calibration expects the encoder to move a quarter turn divided by the ratio; a wrong ratio makes it fail.

Backlash in the gearbox sits inside the loop and can make the axis hunt at rest. Raise the deadband to cover it.

At power-up

Section titled “At power-up”

The S1 reads the encoder once and starts counting from there. The first position is the angle from the saved zero, between −½ and +½ turn. Turns made while the power was off are not known, so:

  • An axis that stays within half a turn of zero (with the on-board encoder: of the motor shaft) comes back exactly where it was.
  • Anything else should be homed after power-up.

The zero is saved with Save to motor, and by Calibrate and Home automatically.

Magnet health

Section titled “Magnet health”

The encoder reports its field strength. Tercio Control lists these on the Diagnostics tab:

Warning Fix
Magnet too weak Move the magnet closer to the chip, or use a stronger magnet.
Magnet too strong Move it further away.

If readings stop, or the magnet disappears while the loop runs, the S1 raises the Encoder fault and switches the bridge off.