VEX IQ Curriculum - Mechanisms
Lifting Mechanisms (Grades 4-8)
Before discussing Lifting Mechanisms, it’s important to know what a Degree of Freedom is. A Degree of Freedom refers to an object’s ability to move in a single independent direction of motion. To be able to move in many directions means something has many Degrees of Freedom. Moving up and down is one degree of freedom, moving right and left is another; something that can move up/down and left/right has TWO Degrees of Freedom.
A Lifting Mechanism is any mechanism designed to move to perform tasks and/or lift objects. With that understood, let’s look at Lifting Mechanism types. In competition robotics, there are three basic types of Lifting Mechanisms: Rotating Joints, Elevators, and Linkages.
The most frequently used lifting mechanism in mobile and competition robotics is a Rotating Joint. Rotating Joints are the simplest Lifting Mechanisms to design and build. In VEX IQ, using a shaft and gears quickly creates an arm that will rotate and lift. This type of Lifting Mechanism moves on an arc, changing both the distance any manipulated objects are from a robot base, and changing the orientation of those objects (relative to their environment) on the way up.
Another lifting mechanism used in mobile and competition robotics is an Elevator. While not as common as the Rotating Joint, the Elevator uses linear (straight line) motion to lift straight up. In VEX IQ, one way that elevators can be built is with Rack Gears and Linear Sliders, both sold as part of the Gear Kit. This type of Lifting Mechanism moves straight up and down, keeping the distance between any manipulated objects and the robot base, as well as the orientation of those objects, consistent on the way up.
Linkages can also be used to build Lifting Mechanisms. Linkages consist of a series of rigid bodies called links, connected together by freely rotating joints. Linkages convert an input motion into a different type of output motion and can be very consistent. For example the input motion could be a Rotating Joint, but the Linkage could produce Elevator-like output motion. In VEX IQ, combinations of different-sized beams, shafts, and/or connector pins can be used to construct a Linkage.
One of the simplest and most common linkage types is the Four-Bar Linkage. This is a linkage system that provides a wide variety of motions depending on its configuration. By varying the length of each link, one can greatly change the output motion. The most basic type of Four-Bar Linkage is one where link pairs are equal length and parallel to each other, as seen below:
Rotating Joint, Elevator, or Linkage?
Elements to consider when deciding what type of Lifting Mechanism is best for your robot’s needs:
- Elevation Required – How high do you have to lift?
- Object Orientation – Do the objects you are lifting have to remain in a certain orientation?
- Size Limitations – Are there design or environmental limitations to your robot’s size?
- Complexity – How many degrees of freedom are desired? What type of hardware is required?
- Motors Required – Do you have enough? Is the total number limited?