Simple dropper post

For a while my dad has been looking into buying a dropper post (similar to a rock shox reverb) that means you can adjust the height of the saddle without having to stop or get off of the bike. As this is quite a specific area with a lot of engineering packaged into a small (typically no more than 34.9mm in diameter) package the prices start at £150. This price was seen to be too high for a simplistic function.

As I only had one week left, at this point, with access to a work shop I designed a simple system that works off a gas strut and four machined pieces of aluminium (two different diameters, as seen in Fig. 1) that work like a quill stem. See Fig. 2 and Fig. 3 as they show an visual explanation of the clamps.

Unfortunately these pieces have a high quality finish on the outer diameter, if this project were to be done again I would specify a knurled finish on the outside surface to provide a better grip on the tubes. However these are working well having been assembled with a grit assembly paste.

Fig. 1 - Machined pieces of aluminium

Fig. 2 - Smallest diameter

Fig. 3 - Largest diameter

The smaller diameter was to inside of the seat post (Fig. 4) and the larger diameter to go inside the seat tube (Fig. 5). There was a lot of trial and error involved in getting the distances inside the tube set up correctly.

Fig. 4 - Inside the seat post

Fig. 5  - Inside the seat tube

At either end of the gas strut used is a M6 10mm thread which meant that one of the bolts (as shown in Fig. 2 and Fig. 3) could have the head threaded to accept the smaller diameter side of the gas strut. On the larger end of the gas strut was an eyelet fitting which was domed (Fig. 6), the dome provided a means or pushing off of the clamp inside the seat tube.

Fig. 6 - Eyelet fitting on the end of the gas strut

Fig. 7 shows a video of the whole system working. This now allows the saddle to be lowered or raised without having to stop if a quick release saddle clamp is used.

Fig. 7 - Completed system

Further work needs to be done to have a bar mounted lever to operate the system so that you don't need to operate a quick release. If more time was available I would not have two toleranced faces as the wear faces (especially in the muddy UK) but as this bike is not often ridden it should be of no detrimental effect.