I went and did a quick search on google online, and found quite a few online courses. Mostly involved teaching about the forms and moves of Taichi. Personally, I feel like a more scientific approach to Taichi is lacking.
So here's my thoughts on Taichi, broken down in to a lesson by lesson. It's structured into a question and answer format. Most of these exchanges were with my Teacher. There are images throughout, so the lessons aren't as dry.
Lesson 1: Purpose of Tai Chi (Theory)
Lesson 2: Stable Line of Gravity (Application)
Lesson 3: Mind Stability (Theory)
Lesson 4: Suspended Focus State (Application)
Lesson 5: Five Points of Gravity (How to Relax in Taichi) (Theory)
Lesson 6: Legs - Downward Gravitational Pull (Application)
Lesson 7: Legs - Muscle Relaxation (Theory)
Lesson 8: Spine - Downward Gravitational Pull (Application)
Lesson 9: Spine - Muscle Relaxation (Theory)
Video 1: Yang Style First Phase · 楊氏 第一段
Video 2: Grasp the Bird's tail · 攬雀尾
Video 3: Raise Hands & Step Forward + White Crane Spreads its Wings · 提手上势 + 白鹤亮翅