隨著近年來運動意識逐漸抬頭，自行車運動現在是被全世界採納為最受歡的有氧運動之一。在騎行的過程中，在期望的速度下找到最佳踏頻去達到高效率的效果是很重要的。此外，自行車運動非常取決於路況的變化，因此設定適合的檔位是關鍵。
一個好的自行車齒輪系統幫助騎行者在變速時，可以平穩地在兩個齒輪間換檔，但此變速系統通常是非常昂貴的。儘管市面上有自動變速系統，但他們通常專門為了某些廠牌的高價位齒輪系統所設計。
在本論文中，我們設計一個自動的自行車變速系統，此系統可以安裝在大多數變速自行車的齒輪系統上，甚至是低成本的變速自行車的齒輪系統。整個系統由變速機構、踏頻檢測器、速度檢測器、藍牙搖桿以及Android APP所組成。我們所提出的系統透過微處理器控制馬達來牽引變速線，達到換檔的效果，而微處理器透過藍牙連結手機。由於Android APP的開發使得使用者除了可以透過藍牙搖桿手動變換檔位，或是透過APP基於騎行和路況(例如：踏頻、道路坡度等)自動變換檔位。在不同的工作負載下進行廣泛的測試，這些測試包含變換檔位速率、訊息傳送速率、不同工作負載下電池的功率消耗等，此系統可以在兩顆18650的鋰電池充飽電的情況下，執行變換檔位超過1500次以上。

Biking is now adopted as one of the most popular aerobic exercises in the world. In biking, it is important to find the best cadence under the desired speed to achieve the best effect. Besides, riding a bike is very much dependent on road conditions. Hence, to set a suitable gear level is crucial.
A good bike gear system helps a biker to have smooth transition between two gear levels, but is usually very expensive. Though there are automatic gear shifting systems available in the market, they are usually designed specifically for high-priced gear systems of certain brands.
In this thesis, we design an automatic bike gear shifting system that can be installed in most derailleur bike gear systems, even the low-cost ones. The overall system consists of a gear shifting mechanism, a cadence detector, a speed detector, a Bluetooth joystick and an Android App. The proposed system uses motors to shift the gear by pulling the gear wires under the control of a microprocessor which is connected to a smartphone by using Bluetooth. An App is developed so that one can manually change the gear level with the Bluetooth joystick or the App can shift the gear automatically based on the riding and road conditions such as cadence, road slope and so on. Extensive tests under different workloads are performed. These tests include shift rate, data communication rate, battery power consumption under different workloads, and so on. The proposed system can perform over 1500 times of gear shifts with two fully charged 18650 Li-ION batteries.

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