J.M. Gabrielse

VEX Grippers(Devices that can attach to

objects)

J.M. Gabrielse

Outline

• Gripper Theory– Control– Speed

• Common Types of Grippers– Servo Grip– Motorized Grip– Pneumatic Grip– Roller Grip

• Challenge

• Hints– Use Lock Bars to attach devices to axles– Use an Ultrasonic Ranger to find objects

Vex Labs Gridiron Robot

J.M. Gabrielse

Control

• Holy grail of gripping:– Get object fast– Hang on– Let go quickly

• This must be done under excellent control– Limit switches– Auto-functions– Ease of operation

J.M. Gabrielse

Speed

• Quickness covers mistakes– Quick to grab– Drop & re-grab

• Fast– Servo gripper– Pneumatic gripper

• Not fast– Roller gripper– Motor gripper

J.M. Gabrielse

Servo Grip

• Precise

• Limited range of motion

• Limited torque

Robert’s ARL robot in 2006

J.M. Gabrielse

Motorized Grip

• Can be geared for speed or torque

• More complex

FVC Team 31 in 2005

J.M. Gabrielse

Some robot

Pneumatic Grip

• Powerful

• Reliable

• Requires entire (unreliable) pneumatics system

J.M. Gabrielse

Roller Grip

• Slow• Allows for

misalignment when grabbing

• Won’t let go• Extends object

as releasing• Simple

mechanism

FVC Team 34 in 2005

J.M. Gabrielse

Gripper Challenge

Vex Challenge #3:

Gripper Due Date: Friday Vex Inventor’s Guide: Vex Inventors Guide (3.3): Motors and Servomotors EasyC for Vex Help: Search for “servo”

C Level Challenge (70 points):

Build a robot that uses a servo to grab an empty soda can o Drive up to the soda can and grab it o Drag the soda can to a designated point o Release the soda can and drive away.

Make a design drawing of your gripper B Level Hardware Challenge (85 points):

Build a robot that uses a motorized grip to grab, drag, and release a full soda can Make a design drawing of your gripper

B Level Software Challenge (85 points):

Build a robot that can complete the C Level Challenge autonomously o You will be given the distance between the starting position and the soda can o You will be given the distance you need to drag the soda can o The robot must return to operator control after releasing the soda can and driving

away A Level Hardware Challenge (100 points):

Build a robot that uses a roller grip to grab a soda can. Make a design drawing of your gripper

A Level Software Challenge (100 points):

Build a robot that can autonomously detect and collect a soda can The robot will be placed in the center of a 6’ x 6’ taped square

with a soda can The robot must find the soda can and bring it back to the center of

the square

Use lock-bars to attach metal pieces to axles

J.M. Gabrielse

Lock-Bars

Lock-bars allow for any component to be attached to an axle and rotated by a motor or servo.

• Axles fit through the square holes.• Bolts fit through the round holes.

J.M. Gabrielse

Ultrasonic Range Finder

• Detect the distance to the nearest object or wall– Bounces sound waves off of objects and measures the time it takes

sound waves to return– The time can be used to calculate distances from 3 cm to 3 m

J.M. Gabrielse

Thanks/Resources

• Designing Competitive Manipulators: The Mechanics & Strategy

by Greg Needel (www.robogreg.com)