Drag Rig — First Field Test

Date: 2026-05-09 Type: Build Log

Context

First physical step toward field-testable hardware. Goal was to attach a basic tick drag to the TRX-4 and run a short manual-driving test on grass — no autonomy, no permethrin, no instrumentation. Just confirm the mechanical rig works before investing in the autonomous drive piece.

Design Decision: Elevated Mount Instead of Towed Bar

The published tick-drag protocol calls for a bar towed behind the rover on the ground, with a flat 1m² cloth dragging behind it. Rejected this design for two reasons:

Snag risk. A bar dragging on the ground catches on twigs, roots, and uneven terrain. Anything the rover's wheels roll over, the bar would also have to roll over — but with no suspension and no power.
Tick behavior. Ticks exhibit negative geotaxis — they climb upward to quest, and once on a cloth they keep climbing toward the highest point. A cloth that's flat on the ground bouncing across uneven grass tends to bump ticks back off, especially at the leading edge. An elevated leading edge gives ticks a "high point" to settle at and stay on.

The 1m² quantitative-sampling rationale that justifies the standard protocol doesn't apply here — this project is about photographing/logging finds, not publishing density numbers comparable to peer-reviewed studies.

What Was Built

~70cm wooden dowel as the leading-edge bar
White flannel cloth attached to the dowel
Two heavy-duty velcro straps, one near each end of the dowel, wrapping around both the dowel and the rear bumper of the TRX-4
Bar sits at bumper height (~5") above the ground; cloth drapes back and down from there

Velcro chosen over zip ties (one-shot, not removable) and carabiners (would require drilling the bumper). Bonus: velcro acts as a soft-failure point on hard snags.

Test Run

~5 minutes of manual driving on grass
Handling: totally fine. TRX-4 drags it like it isn't there.
Coverage: cloth had decent ground contact behind the rover.
Obstacles: moved over small branches etc. without issue.
No slits cut in the trailing edge yet.

Files Modified

None — purely physical hardware work.

Key Takeaways

Elevated-mount design works mechanically. No need to revisit the towed-bar geometry.
Velcro mount lets the rig come off in seconds for storage / body removal / cloth swaps.
Trailing-edge slits still TBD — expected to further reduce snag risk on twigs by letting the cloth flex around obstacles instead of resisting as one piece.
Run was short; need a longer test on more varied terrain to see how it holds up.
The build-06-drag-cloth.md article still describes the old towed-bar design and needs to be rewritten to match what was actually built.