# voxl-mapper local planner: "Cannot insert trajectory. Total segments = 20, Max segments = 20" — replanning never reaches the drone during Follow Path

Source: https://forum.modalai.com/topic/5510/voxl-mapper-local-planner-cannot-insert-trajectory.-total-segments-20-max-segments-20-replanning-never-reaches-the-drone-during-follow-path
Category: Autonomy: VIO, Mapping and Navigation (https://forum.modalai.com/category/19/autonomy-vio-mapping-and-navigation)
Posted: 2026-10-13 06:03:21 UTC by 김진혁
Replies: 0 · Views: 18

## 김진혁 · 2026-10-13 06:03:21 UTC

We flew our first mapper-based path flight on a Starling 2 Max and the drone did follow the planned path. However, the local planner was unable to deliver a single trajectory for the entire flight, so the drone was flying on the one path computed before departure, with no replanning.

**What happened**

Global planning succeeded:

```
05:13:38  Client requested plan to location
05:13:38  Using start pose of: x: 1.67, y: -0.80, z: -1.46
05:13:38  Using goal pose of:  x: 5.16, y: -1.34, z: -0.89
05:13:38  Starting RRTConnect planner
05:13:38  Immediate collision free path found!
```

Then, from the instant we pressed **Follow Path**, this repeated continuously for 2 min 16 s until we took manual control:

```
05:14:10  Client requested to follow last path
05:14:10  Local Planner failed to send trajectory
05:14:10  ERROR: Cannot insert trajectory. Total segments = 20, Max segments = 20
...       (repeats at roughly 1-2 s intervals through 05:16:26)
```

Throughout those 2 min 16 s the planner itself was running normally — `A* took = 0.07-0.14 ms for 13 iterations` and `Smoother took = 6-12 ms` were interleaved with every failure. So it computes a trajectory and then cannot insert it.

The drone moved 2.68 m straight-line / 8.79 m total path at up to 1.04 m/s, which matches the pre-computed path. It stopped 0.81 m short of the goal only because the pilot intervened.

**What we ruled out**

1. **Not a planning failure** — the global path was found and reported collision-free.
2. **Not a VIO problem** — dt held at 33.3 ms for all 44 samples in flight, features 15-30, `cs_ev_pos` / `cs_ev_yaw` / `cs_ev_hgt` all True.
3. **Not a map problem** — `voxl_mapper_aligned_ptcloud` was producing 1,489-2,925 points at ~10 Hz before and during the flight.
4. **Not CPU load** — load average dropped from 7.75 on the ground to 4.5 in flight; governor was `performance`.
5. **Not thermal throttling** — 94-96 C, but `scaling_cur_freq` equalled `cpuinfo_max_freq` on all cores and `dmesg` showed no throttle events.
6. **Not a config we changed** — `voxl-mapper.conf` is stock; `loco_num_segments` is 10.

**What we could not find**

The limit of 20 does not appear in `voxl-mapper.conf`. `loco_num_segments` is 10, which is not the number in the error. We could not locate a setting that exposes `Max segments`.

**One thing we suspect, but have not tested**

Before the successful `Go`, we had two failed ones — both rejected with `ERROR: End point is in collision` because the goal came in at `z: 0.00` (we were clicking in the 2D view, which puts the point at ground level). The `Max segments = 20` error appeared **immediately** on the first Follow Path, which makes us wonder whether failed plans leave segments behind. We have not yet tested whether pressing **Clear Paths** first avoids it.

**Questions**

1. Where is the 20-segment limit set, and is it configurable?
2. What normally fills the segment buffer, and what clears it? Does a failed `Go` leave segments allocated?
3. Is `Clear Paths` the correct way to reset this state before `Follow Path`?
4. Is there a way to detect this condition other than reading the mapper journal? From the Portal UI everything looked correct — the path was drawn and `Immediate collision free path found!` was reported — so an operator has no indication that obstacle avoidance is not active.

**Environment**

- Hardware: Starling 2 Max, SKU `MRB-D0012-4-V4-C29-T8-M36`
- `voxl-version`: system-image `1.8.08-M0054-14.1a-perf`, voxl-suite `1.6.4~beta5`
- `voxl-mapper` 0.2.4, `voxl-vision-hub` with `offboard_mode: "trajectory"`
- Services active at the time: `voxl-vision-hub`, `voxl-open-vins-server`, `voxl-mapper`, `voxl-px4`, `voxl-portal`

We have the full mapper journal and the PX4 `.ulg` from this flight and can share either.