How to Decide on a Manipulator

Moving objects is one of the functions that robots are designed and assembled to perform. These objects may either be a component/assembly on the robot or an external object. The objects are manipulated so these robot assemblies are called manipulators.

Whether robots are being created for a classroom game or a robotics competition, effective and efficient manipulators give the robot a competitive advantage. Game strategy analysis should be the starting point when deciding on a manipulator. That means asking, "How is the robot going to play the game?". Some factors to consider are matching the assembler's level of experience and knowledge to the complexity of the design; and assessing the amount of time available to assemble the design.

For example, in the VEX Robotics Competition 2019-2020 game, Tower Takeover, a plow could be quickly and easily be attached to a drivetrain which allows the robot to push the Cube game pieces into the Goal Zones. Whereas, assembling a double reverse 4-bar with a roller claw which would allow the robot to score and de-score Cubes out of the highest center Tower and stack multiple Cubes in the Goal Zone, would require much more planning and time to assemble.

One of the advantages of the VEX EDR system is it allows for many designs and a nearly endless opportunity for creativity. This allows for a wide variety of different types of manipulators and most likely new designs which have yet to be assembled. In order to provide a starting point, here are some descriptions of different types of manipulators.

Passive Manipulators

Passive manipulators have no actuators, or in other words, there is no motor or pneumatic cylinder which is directly attached to the manipulator. The rules of many robotics games include limitations on the number of motors and/or the amount pneumatic air storage a robot can possess. Designing a passive manipulator allows the robot’s actuators to be used for additional functions. Passive manipulators are moved by being attached to a drivetrain or another active manipulator. They can also contain stored energy from Rubber Bands or Latex Tubing. Passive manipulators can be some of the easiest and quickest types of manipulators to assemble, although they can be very complex with manual releases and re-set mechanisms.

Some examples of passive manipulators which can be used to play a robotics game include:

  • Plows are usually attached to the drivetrain and typically their functions are pushing game pieces around and/or keeping the robot from driving up on game pieces and becoming immobile.
  • Forks and scoops (types of passive claws) are typically attached to an arm and are usually designed to slide under game pieces in order to pick them up. 
  • Shields are designed to keep game pieces off of the robot. 
  • Game piece slides are designed to allow game pieces to slide out of the slide and into the goal or scoring zone.
  • Expansion zones allow the robot to expand beyond its starting position after a match begins.
Passive Plow

For more information about this topic, please see: How to decide on a Passive Manipulator.

Active Manipulators for lifting objects

Active Manipulators move by having an activator such as a pneumatic cylinder system or a motor. Motors can directly drive the active manipulator. Motors can also move manipulators when assembled in combination with a gear train, chain and sprocket system, Linear Motion Kit, Turntable Bearing, or other parts available in the Motion Product line. Typically, active manipulators take more time and planning to assemble than passive manipulations.

Some examples of active manipulators which can be used to lift and place objects in a robotics game include:

  • Arms are usually attached to a tower on the robot chassis and are used to lift another manipulator on the end of the arm or to lift the robot off the ground.
  • Claws are usually attached to an end of an arm and are used for grasping an object.
  • Gates and basket/collectors are designed to hold multiple game pieces.
  • Lifts are assembled to lift other manipulators vertically or to lift the robot off the ground.
V5 Clawbot 4-Bar Arm V5 Clawbot Claw

For more information about this topic, please see: How to decide on an Active Manipulator for lifting objects.

Active Manipulators for throwing an object

Some robotics games have an element of play where there is a competitive advantage to throw game objects. These manipulators are typically attached directly to the robot chassis. They are usually activated using a motor, a motor with a gear/sprocket system, or a pneumatic cylinder system. Active throwing manipulators are often paired with sensors to help control the throw. They also require a great deal of planning and time to assemble.

These manipulators usually consist of a pickup and transfer system and a throwing system such as:

  • Roller intakes and conveyor belts move game pieces from the game field into the robot and usually into the throwing system.
  • Flywheels throw game pieces by having the game piece come in contact with a spinning wheel.
  • Slingshots are designed to use Rubber Bands or Latex Tubing to fling the game piece.
  • Catapults throw game pieces with a lever arm.

For more information about this topic, please see: How to decide on an Active Manipulator for throwing an object.

Selecting the Manipulator

Each game has its own unique set of requirements for manipulators. There is no correct design for any given game, although there are manipulators which are more competitive. The most competitive manipulators are usually the ones which work effectively, quickly, and consistently.

Structural metal and hardware can be purchased at https://www.vexrobotics.com/vexedr/products/structure.

Wheels and other motion hardware can be purchased at https://www.vexrobotics.com/vexedr/products/motion.