This Bullet example demonstrates an issue of the btGeneric6DofSpring2Constraint regarding the relationship between pendulum length and frequency. The simulation shows 6 pendulums oscillating about a point on the vertical axis through the origin. The 3 upper pendulums (pendulum 1-3) are constrained by btGeneric6DofSpringConstraint, while the 3 lower ones (pendulum 4-6) are constrained by btGeneric6DofSpring2Constraint. It is obvious that pendulum 1-3 oscillate at different frequencies, the shortest with the highest and the longest with the lowest frequency. This is physically correct. However, pendulum 4-6 oscillate at the same frequency indicating a bug in the btGeneric6DofSpring2Constraint resulting in incorrectly simulated dynamics.

1. Clone bullet from https://github.com/bulletphysics/bullet3

2. Follow installation instructions on http://bulletphysics.org/mediawiki-1.5.8/index.php/Installation or on Linux do:

	cd path/to/bullet
	mkdir bullet_build
	cd bullet_build
	cmake .. -G "Unix Makefiles" -DINSTALL_LIBS=ON -DBUILD_SHARED_LIBS=ON
	make -j4
	sudo make install

4. Clone bullet_spring_constraint_demo

5. Compile bullet_spring_constraint_demo with:

	cd your/path/to/bullet_spring_constraint_demo
	mkdir build
	cd build
	cmake -DBULLET_SOURCE_DIR:STRING=/your/path/to/bullet/source/directory -DBULLET_BUILD_DIR:STRING=/your/path/to/bullet/build/directory ..
	make

6. Run AppSpringConstraintDemo