Hybrid of Hart's A-frame and Chebyshev linkage
Hybrid of Hart's A-frame and Chebyshev linkage
Hart's A-frame and Chebyshev linkage are very similar each other.
In Chebyshev linkage, 
sin(0.5 ∠BFD) + sin(0.5 ∠AED)  ≒ constant
is true.
WHY?
(IF you know Hart's A-frame, its fact is evident, maybe.)
■ CQ length calculation by another way
from Hart's A-frame law,
CQ×QD = DE×EA 
is true, so   
CQ = sqrt(DE×EA)=sqrt(1×5)=√5     (∵ CQ=QD)