The geometric conditions for the presence of a crank in a hinged four-bar mechanism are as follows:
a. The sum of the lengths of the shortest rod and the longest rod is less than or equal to the sum of the lengths of the other two rods;
b. The shortest rod must be a connecting rod or a frame. When the shortest rod is a connecting rod, the mechanism is a crank rocker mechanism. When the shortest rod is a frame, the mechanism is a double crank mechanism. Read the question below:
1. Double crank: AD rod is the shortest and AD+130≤10110, so 0