Motorized Dropper Post Assembly by Trek

In this article, we’ll be discussing a Motorized Dropper Post Assembly by Trek, US publication 20200346703. The publication date is Nov. 5th, 2020 and the filing date is Apr. 30th, 2020. This patent is a related to provisional application 62/840,440 filed Apr. 30th, 2019. Provisionals are short patents used to effectively ‘save a spot in line’. It gives inventors one year to file a full patent. Provisionals are not published.  

Brief Summary (tl;dr)

Trek are introducing a new dropper post that utilizes a screw-type linear actuator mechanism. The upper and lower parts of the seat post are connected via a long screw. The upper part of the seat post has a threaded nut attached to the screw. There is a motor at the bottom of the dropper that rotates the screw. As the motor rotates the screw, the upper part of the seat post moves up and down. It’s a very simple design.

Background

Today we’re talking about dropper posts. For those that are not aware, a dropper post is a seat post that holds your seat in place. With the flick of a switch, the rider can both lower and raise the seat to a desired position by applying or removing your weight from the seat. Typically, the seat post is in a high position for climbing and in a low position for going downhill. The ability to get the seat out of the way for downhill trails has been a major advancement in safety. If anyone remembers going downhill, sitting high up on the bike, remembers how scary it is.

If I had to pick the most important part of my bike, I’d have to say it’s the dropper post. I will never ride a bike without a dropper post. I think this sentiment is shared with many people. It’s been such an important invention for mountain biking and the design has been refined so well that most of them just work. Pick any one of them and you’ll probably be okay. I’m currently running the KS Lev, and it’s been working great.

Intro

Currently, there are numerous designs for dropper posts, from fluid-actuated droppers such as the Rockshox Reverb, to the cable-actuated droppers such as the Specialized Command.

Recently, companies such as SRAM have introduced electronically actuated dropper posts, where the system is completely wireless. SRAM (US20200255078) do say that they have a motor in their dropper post, but they make it clear that it is an ‘actuation device’, meaning the movement of fluid is dictated by a motor assembly.

The actuation device 63 may alternatively include other actuation configurations, such as an electromechanical motor, a cable actuation device, a hydraulic actuation device, or other actuation facility.

Additionally, Specialized (US10081405) have a motor in one of their seat post designs, but the motor also actuates a device like and on/off switch.  

…wherein the at least one servomotor is configured to selectively move the at least one movable member between a radially expanded position and a radially retracted position.

So, the idea of a motor in a seat post isn’t new, but Trek are introducing the motor is a different way. This is one of those patents that looks complex, but it’s actually very simple in theory. Implementation is always a different story.

Intended novelty

I haven’t seen, and cannot find, a motorized seat post similar to this design because Trek are using what they’re calling a ‘lead screw’ to move the seat post up and down. This is basically a screw-type linear actuator.

The lead screw is located in the lower section of the seat post and is rotated with a motor. The upper side of the seat post, the part that goes up and down, is threaded and moves as the lead screw rotates. If my memory serves me correctly from school, these types of linear actuators are pretty bulletproof. Another example of a device with a linear actuator is the table (or head) of a 3D printer.

Why

Trek state:

A typical bicycle dropper post is small in diameter (e.g., 31.6 millimeters (mm) or 34.9 mm), and a challenge in designing dropper posts involves minimizing the height of the internal mechanisms to allow the post to fit into small frames.

It appears as though this is being designed for a smaller packaged dropper post.

Additionally, Trek state an advantage of using less bearings.

In a typical linear motion application that has loads of several hundred pounds, the bearing assembly that supports the lead screw and prevents the motor from seeing an axial load has to be designed to operate efficiently while withstanding the high loads. Typically, this is done with multiple bearings that support the end of the lead screw radially and axially… The proposed motorized dropper post can also utilize just a single bearing mechanism, which allows the dropper to operate efficiently under loads required to move the saddle, while also preventing high axial loads from being transferred into a motor of the system.

Trek also state that a single bearing is:

…low cost, compact, and generate[s] a very limited amount of noise, which improves the experience of the user.

What

Trek have designed a dropper post with a screw that is used to raise and lower the seat post and have simplified the necessary bearings in a dropper post design. There is an interesting little section that suggests this can be a wireless system and may also be integrated into a smart-bike that moves the seat post automatically.

In at least some embodiments, the assembly can include a computing system that includes at least a processor and a memory. The memory can be used to store algorithms, software, etc. in the form of computer-readable instructions to perform any of the operations described herein. Upon execution of the computer-readable instructions by the processor, the computing system performs the operations to control the assembly… The computing system can further include a transceiver that enables wireless communications between the computing system and a user device.

In another example scenario (par. [0067-68]), Trek spell out that this dropper may be able to be set to an upper and lower limit and the system. So, the way I’m reading this, the system would be able to save certain positions (high/low/etc.) and the rider can select certain locations of the seat post on the fly (memory device).

How

First, we’ll talk about the lead screw. Fig. 2C is the upper part of the lead screw, so this is a view of the top-out condition, where the seat post is at the top of it’s travel. Fig. 2D shows the bottom of the bottom side of the seat post. Fig. 2C and 2D show motor 230 and lead screw 235. The lead screw nut 240 is threaded and is attached to the upper part (upper tube 210) of the seat post. The motor rotates the lead screw and like magic, the seat post moves.

The lead screw nut 240 is mounted to the upper tube 210 and is also threaded onto the lead screw 235 such that rotation of the lead screw 235 causes the lead screw nut 240 (and the upper tube 210 to which the lead screw nut 240 is mounted) to translate up or down depending on the direction of rotation of the lead screw 235.

Additionally, Trek state this design allows them to use one bearing, bearing 278. This bearing is located near the top of the motor and allows for a smooth and concentric rotation of the lead screw. This bearing, along with the o-rings 262, 264, 266, 286, 288, and 290, and the lead screw sheath 245 help keep the lead screw going perfectly straight to reduce the chance of binding in the screw.

Trek state the lead screw may be made of carbon or stainless steel and the nut can be made of plastic, rubber, or another non-metalic material to reduce noise.

As someone that does work on my bikes, I would love to have this dropper. No bleeding lines, no cables to change, no IFP, no air pressures, nothing. I love it. This appears to be very simple to maintain. Just make sure the bearing is clean, the o-rings and lead screw are clean, and you’re good to go. The only thing I’m wondering is the weight. Motors typically aren’t light (for their size) and the lead screw may be a little heavy, assuming it’s metal. To that point, if it’s plastic or carbon, then my concern goes to binding and junking the threads too easily.

Either way, it’s a cool little design and I hope Trek will send me one to test! Thanks for reading!

3 thoughts

  1. For me, the most attractive potential of this design is the ability to drop it without sitting on the seat. While the current dropper operation method has become second nature, it would be incredible for it to get out of your way so you can focus on the trail.

    Like

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