Marine Lift Steering Mechanism

problem:

Design a mechanism to ensure that the front wheels of a large marine lift (used for moving boats into and out of the water) are appropriately rotated so that the tires do not scrub when driven around corners. This achieves a tight turning radius.

solution:

  • 6-Bar function generator.
  • Input controlled by hydraulic pistons.
  • Designed by Lisa Logan and A. Erdman, University of Minnesota, using Lincages 4.

animation (overview):

The "Length" boxes at the left represent the extension of the actuators. As can be seen, the top piston extends by the same amount that the lower piston retracts. This is achieved by designing the hydraulic controller to move the same amount of fluid in and out of each piston. This leaves the function generator mechanism to ensure that the wheel on the inside turns more than the wheel on the outside.



picture of final machine:

This picture shows the final design of the ISL 80, a large marine lift built by Marine Travelift Inc. of Sturgeon Bay, WI. It is powered by a 300 horsepower diesel engine, and can lift 160,000 pounds. It is 39 feet tall, 53 feet wide, and has a wheelbase of 30 feet. It has a turning radius of 63 feet at the outside front wheel, and 0 feet at the inside rear wheel.



animation:



kinematic diagram: