Deceleration distance too long

the machine is configured with MAX_ACCELERATION = 500mm/s².
I move with G38.2 F3000 to the probe switch.
At F3000 (=50mm/s) expected deceleration distance is 2.5 mm (V²/(2*a)).

But the braking distance is about 5.1 mm.
This corresponds to a deceleration of 250mm/s².
So the machine brakes with half the deceleration. (250 mm/s² instead of 500 mm/s²)

What is the reason for this?

LinuxCNC is 2.9 master

I think posting your .INI file might help.

I agree with you

ini attached.
It's about the Z axis

When moving with the jog buttons the acceleration is correct






When moving in MDI or program the acceleration is half




Hmmm... bug or feature?

There is no rotary axis. Just a simple move likeThe same behavior is in X axis: Jog acceleration is ok (200); MDI acceleration is half (100)

I get the same response:

MDI at 1/2 programmed accel limits
GCode (G0 G1 at least) and jogging at full speed
Not setup to try G38

2.8.1 and 2.9 are identical in this respect

The acceleration seems to be independent of the feed rate

I suspect the cause of the acceleration difference is that unplanned
moves are treated differently by the TP

Doesn't jogging use an independent "planner"?