Can a drive switch between modes on the fly?

Yes — most industrial servo drives and modern BLDC controllers support mode switching at runtime (often called "mode of operation" in CANopen/EtherCAT CiA 402 profiles), and it is common practice: for example, running position mode for a rapid approach move, then switching to torque mode for the final compliant contact phase, as in screw-driving or press-fit operations.

Does velocity mode use any position feedback at all?

The tachometer or encoder feedback used to compute actual velocity often comes from differentiating position feedback, so a position sensor is frequently still present in the loop electrically. The distinction is that the velocity loop's error signal is speed error, not position error — there is no position setpoint being compared against, so accumulated position drift is never corrected.

Is torque control the same thing as current control?

For a permanent-magnet brushless or DC motor, torque is directly proportional to current (through the motor's torque constant, Kt), so "torque loop" and "current loop" are frequently used interchangeably and are, in practice, the same regulated quantity. The distinction becomes more meaningful in machines where the torque constant itself varies with position or saturation, requiring compensation to keep the current loop's output an accurate torque command.

Why does position mode feel "stiff" and torque mode feel "soft"?

Position mode actively drives torque output to eliminate any position error, so pushing on a position-controlled axis is met with proportionally increasing resistance — that is mechanical stiffness created entirely by the control loop (virtual stiffness), not the physical structure. Torque mode applies a fixed, bounded torque regardless of resulting motion, so an external push simply moves the shaft with no loop fighting back — that is what "compliant" or "soft" means in a control context.

What happens to position accuracy if you run velocity mode for a long time?

Position error accumulates without bound, because nothing in the loop is ever comparing actual position to a target. Small velocity tracking errors integrate over time into arbitrarily large position drift — which is exactly why applications needing both speed regulation and periodic position correction (like some indexing conveyors) will run velocity mode most of the time but briefly switch to position mode, or add an outer supervisory correction, at defined checkpoints.

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Concept Explainer · Mechatronics

Position vs Velocity vs Torque Control

The same servo drive, the same motor, the same PID math — but which variable the innermost loop is told to hold constant changes everything about how the axis behaves.

Every modern servo or BLDC drive can run in at least three control modes, and picking the wrong one is one of the most common reasons a mechatronic axis feels "wrong" even though the tuning gains look fine. Position, velocity, and torque control aren't three different algorithms — they're the same cascaded PID structure with the command target moved to a different rung of the ladder. What the loop is told to hold at the commanded value determines what the system does when it meets a disturbance it didn't expect: a jam, a collision, an external push, a changing load.