Tuning

The defaults suit a NEMA 17 with a light load. When the axis should be stiffer, quieter or faster, these are the knobs, in the order worth trying them.

The loop

Every 50 µs the S1 computes a velocity for the step generator:

v = v_ref + Kp·e + Ki·∫e dt + Kd·(v_ref − v_meas)

Feed-forwardv_ref is the motion profile’s own speed, so a well-matched motor tracks a move with almost no correction.

The errore is where the profile says the shaft should be, minus where the encoder says it is.

Limited outputThe correction is capped at twice Max velocity, and its rate of change at four times Max acceleration, so it never jerks the motor out of step.

Deadband at restErrors inside the deadband are ignored and the integral is frozen, so encoder noise never turns into hunting.

A tuning session

Tercio Control’s Tuning tab has what you need: a live chart of position, velocity or following error, the Position loop gains with Apply, and a Step response test.

1. Pick a step size typical for your machine and select Run step. The motor moves by the step, measures for 1.5 s and moves back.
2. Read the results: rise time (10 % to 90 %), overshoot, settling time (to within 2 % of the step), peak and final error.
3. Change one gain, Apply, run the step again. Repeat.
4. Save to motor when you are happy.

Current and chopper

Setting	Default	Guidance
Run current	1500 mA	About 70 % of the motor’s rating to start. More current gives more torque and more heat. Capped at 1770 mA.
Hold current	50 %	Current at standstill. Lower runs cooler; higher resists more when pushed.
Quiet mode (StealthChop)	On	Near-silent at low speed.
Quiet mode up to	1 motor rev/s	Above this speed the driver switches to SpreadCycle, which keeps torque at speed. 0 keeps StealthChop at all speeds.

If the motor loses torque or stalls at speed, check the switch speed first, then raise the supply voltage (up to 28 V) before raising the current.

Microsteps

The step generator makes up to 500,000 steps per second, so the microstep setting caps the top speed:

Microsteps	Steps per turn (200-step motor)	Top speed
1/8	1,600	312 turns/s
1/16	3,200	156 turns/s
1/32	6,400	78 turns/s
1/64	12,800	39 turns/s
1/128	25,600	19.5 turns/s
1/256	51,200	9.8 turns/s

The TMC2209 interpolates to 1/256 internally whatever you choose, so 1/16 is already smooth. Choose finer microstepping for slow, very smooth motion; coarser leaves more headroom for speed. A stepper’s torque drops long before these speeds, so for most machines anything from 1/8 to 1/32 is fine.

Position loop gains

Gain	Default	Unit	Effect
Kp, proportional	20	1/s	Correction speed per unit of error: with 20, an error of 0.01 turn is corrected at 0.2 turns/s. Higher is stiffer and settles faster; too high buzzes or oscillates.
Ki, integral	0	1/s²	Removes a steady error under constant load, such as gravity on a vertical axis.
Kd, damping	0	—	Acts on the difference between planned and measured speed. Can calm overshoot on fast moves; the measured speed is noisy, so too much adds buzz.

Kp is the one to start with. Raise it in steps of about 25 % until the step response starts to overshoot or the motor sounds rough at standstill, then back off a step. Values from 10 to 60 cover most setups.

Ki only if an error remains at rest under load. The shaft behaves like a pure integrator of the commanded speed, so with PI control the response is critically damped at Ki = Kp² / 4 (100 with Kp = 20). Start at a quarter of that and raise it until the error goes away within your settling time. More causes slow, rolling overshoot. The integral term is limited to half of Max velocity.

Kd usually stays at 0. If a stiff, fast axis overshoots, try small values and compare step responses.

Deadband

The Deadband (default 0.0005 turn, 0.18°, about two counts of the on-board encoder) is how close is close enough at rest. Once the error falls inside it, the S1 stops correcting; it corrects again only when the error grows past twice the deadband.

• Motor hums or ticks at rest: raise the deadband a little.
• Resting error too large for the job: lower it, and consider an encoder with more resolution.

Stall detection

A stall is a following error larger than Stall threshold (default 0.05 turn, 18°) that lasts Stall confirm time (default 50 ms). The S1 then stops and holds, and raises the Stall fault; the next move clears it.

• False stalls during hard accelerations: raise the threshold a little, or lower the acceleration.
• Late detection of a blocked axis: lower the threshold.
• Stall confirm time 0 turns stall detection off. Not recommended.

Speed limits

Max velocity and Max acceleration bound every move, and the correction can reach twice and four times those values. Rather than guess, run auto-tune with the real load: it keeps the fastest level that passes three times.

Symptoms

Symptom	Try
Hums, ticks or hunts at standstill	Raise the deadband; lower Kp; lower the hold current.
Overshoots and rings after a move	Lower Kp; lower Ki; try a small Kd.
Settles slowly	Raise Kp.
Stays slightly off target under load	Add Ki (see above).
Stalls when accelerating	Raise the run current; lower Max acceleration; check the stall threshold.
Loud at low speed	Turn on quiet mode (StealthChop).
Weak at high speed	Raise the supply voltage; check Quiet mode up to; use coarser microsteps.