Kane Components built a hydraulic-free dropper seatpost from scratch, and it does not work reliably. The binding mechanism fails to generate enough clamping force to hold a rider's weight, making the post sink under load.
The design is worth studying anyway. Kane adapted a woodworking bar clamp principle: two pairs of angled plates at opposing angles lock against an internal rail, resisting both downward rider load and upward return spring force. A cable-actuated cam releases the plates, and an air spring handles return. Salvaged bushings and a lower tube from a broken commercial post reduced the machining burden, with thread milling used to make the mechanism a swappable cartridge. The upper section is aluminum tubing and a custom seat clamp, press-fit together, which proved to be a failure point.
The full build log documents specific failure modes worth reading: cable pull introducing unwanted lateral movement in the post, mechanical jamming traced to the ball end of the cable fouling against the outer housing, and the press-fit upper assembly separating under use. None of these are fully solved. If you want to understand why commercial dropper posts cost what they do, this build is the answer.
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