The Link Set
A lot of LightWave motions are cycles, but not ones that regularly repeat. The simple turning of a crank is a cycle (because it turns a full circle and returns to its starting point). LightWave will let you continuously repeat cycles, but in many cases (like the crank) the cycle may not happen smoothly. The crank may turn quickly at first and then slow down. You may turn the crank first one way then uncrank it back to its original position.
In all of these cases LightWave's cycle controls don't help you; your only option was to hand-keyframe the motion you wanted. This is usually painful, especially if your cycle is something more complex than turning a crank. How do you handle making the turning gears, spinning flywheel, and reciprocating pistons of a steam engine? As it slows and stops, do you really want to hand keyframe every aspect of its motion? It could easily be thousands of keyframes to set!
The Polk's linking plugins solve this problem and many, many more. It can take any motion (a walk cycle, a turning wheel, a gun firing, a drawbridge raising) and allow you to define the base motion just once, then quickly and easily control the entire complex behavior with just one control.
You can specify the phase of the cycle. This might allow you to raise and lower the drawbridge, including turning the gearing and lowering the safety gates, by animating just one parameter from "up" to "down". Another application may have a giant walking robot with hydraulic pistons to move its arms. You may have hoses spanning the elbow joint of the arm, and when the joint opens and closes, the Link plugin can automatically make the hoses bend to compensate.
You can animate the motion by a throttle setting. When your steam engine is slowing down, you can just change one parameter slowly with time, from fast to slow to stop.
You can link the motion to the speed or acceleration of a control. You can set up the needle of a speedometer in a dashboard, and it will automatically rotate to show the true speed of the object. You could link the size of a rocket flame to be based on the acceleration of a space fighter.
Finally, you can control the motion by distance traveled. When a locomotive moves down its rails, the wheels turn based on that motion. The Link plugins allow you to just animate the train- the plugin will take care of spinning the wheels, and moving the tie rods. You can build a spider with articulated legs. By simply "driving" the spider around, the legs will automatically pick themselves up and move forward. You can even make each side of the spider animate at different speeds or directions if it turns in a circle or in place.
It's difficult to try to list the enormous number of applications the Link plugins allow you to do. If you make animations that feature complex motions, you need these tools. If you don't make these kinds of animations, these tools will allow you to start!