When the small circle moves on the outer wall of the big circle, let the radius of the small circle be R. Then the radius of the big circle is Dr. When the circumference of the small circle makes a circle, the circumference of the small circle is 2πr. The arc is equivalent to the radian of the big circle, which is 2π r/dr = 2π/d. At this time, the rotation angle of the small circle relative to the center of the big circle is
2π+2π/d=2π(d+ 1)/d
When the small circle revolves around the big circle,
The walking angle is [2π (d+1)/d] * d = 2π (d+1) π.
It's d+ 1 cycle.
Similarly, if the small circle moves along the inner wall of the big circle, it is d- 1 circle.
According to the topic D=3, there is.
When the small circle moves on the outer wall of the big circle, the small circle rotates four times;
When the small circle moves on the inner wall of the big circle, the small circle rotates twice.