I ntroduction to lifts & manipulators

1. Introduction to lifts & manipulators

2. Lift Concepts Lifts • Four Bar Mechanisms • Rotary Jointed Arms • Scissor Lifts • Telescoping Lifts • Combined Systems

3. Scissor Lifts Lifts Overview • Unique: no straight support; but rather linked and folding supports stretch platform upwards • Powered by hydraulics or motors; bumpy ride • Doesn’t travel at constant velocity; faster during middle of journey/slower with more extension Pros • Max height of platform is adjustable • Height determined by # and length of linkages • Great for straight lifts Cons • Requires huge force to start the lift • Synchronizing two scissors is difficult • Complex design

4. Rotary Jointed Arms Lifts Overview • Basic principle of human arm: shoulder, elbow, wrist • Different types of manipulators (i.e. gripper) can be attached Pros • 3 axes of motion: pitch, yaw, roll • Can emulate human arm • Useful when gripping objects is objective Cons • Failure of joint caused by pressure at shoulder and base plate • Each joint requires a motor; operated independently • Thus, programming is tricky

5. 4 Bar Mechanisms Lifts Overview • Simple and effective • Opposite bars remain parallel, retaining orientation of object Pros • Simple, effective • Object retains orientation • Only one joint to motorize • Easily programmed • Provides reach Cons • Joint may endure heavy pressure • Required to lift “outside of the box” • Vulnerable to side hits

6. Telescoping Lifts Lifts Overview • Commonly used within forklifts and cranes • Extend in one direction • Powered by chain or piston • Also referred to as extension lifts Pros • Extends “within the box”; mechanism protected by base • Operates on a relatively uncomplicated system • Requires only one power source Cons • Multiple segments translate up; higher center of gravity • Can become complex

7. Combined Systems Lifts Overview • Combining systems can help when one doesn’t cut it Pros • Combines the pros from the various lift mechanisms used Cons • Can quickly become too complex

8. Manipulators Manipulators Strategy • What is being manipulated? Types of Intake • Continuous • Single Storage Acquisition Zone Placements / Alignments / Accuracy Grip of Object • How much friction is needed? Motors and Servos Limits Gear Ratios

9. Strategy Manipulators • Find out about the game • Make requirements • Determine drive train • Determine best lift mechanism • Determine best manipulator • If robot doesn’t drive efficiently, arm and manipulator will be useless. • K.I.S.S.

10. What Is Being Manipulated? Manipulators Ball • Continuous and single object grabbers are useful Types of Manipulators • 2 tank treads horizontally / vertically aligned • 3 / 4 prong grabber • 2 point grabber / fork • Bucket intake • Roller • Use soft grip to effectively control and contain the ball

11. What Is Being Manipulated? Manipulators Ring • Continuous and single object grabbers are useful Types of Manipulators • 2 tank treads horizontally / vertically aligned • 3 / 4 prong grabber • 2 point grabber / fork • Bucket intake • Roller • Use soft grip to effectively control and contain the ring

12. What Is Being Manipulated? Manipulators Square • Continuous and single object grabbers are useful Types of Manipulators • 3 / 4 prong grabber with grip • 2 point grabber • Use strong grip to effectively control and contain the square

13. What Is Being Manipulated? Manipulators Triangles • Single object grabbers are useful Types of Manipulators • 3 / 4 point grabber • Flat bottom and X shaped intake roller • Use strong grip to effectively control and contain the triangle

14. Storage of Objects Manipulators • All items of same size can be similarly stored • Stack • Tank treads • Divide • Dump tank (basket) • Simply grab and drop to goal

15. Storage of Arm & Manipulator Manipulators • Must be decided with base so arm and manipulator can be stored when • Trying to fit the size • Effectively obtain objects • U-shaped base • 360˚ pivot joint (& arm extender) • Manipulator attached to base

16. Acquisition Size Manipulators • Intake area of the object • Large intake area is optimal • During match, easiest and fastest for driver(s) • Get multiple objects at once • Keep in mind type of object that will be manipulated

17. Placements, Alignments, Accuracy Manipulators • Scoring object on/into goal must be accurate and easy • Optimal stability and accuracy during scoring • Alignment: know how mechanism works and where it needs to be positioned • Drivers should easily be able to work with placement; manipulator should be accurate

18. Grip of Object & Friction Needed Manipulators Why is grip important? • Manipulator has to efficiently contain the object How do you obtain grip? • Friction

19. Motors and Servos Manipulators • Enable arms and manipulators to move Motors • Can turn a shaft CW and CCW as many degrees as desired • Used for continuous intake Servos • Can turn a shift CW and CCW, but only 180˚ in each direction • Used for <360˚ pivot joints

20. Limits Manipulators Types of Stops/Limits • Hard stop • Sturdy metal part of robot • Physically doesn’t allow arm / manipulator to go any further • May burn a clutch / break motor • Soft stop • Limit switches • Limits should be placed anywhere where there is a hard stop

21. Gear Ratios Manipulators • Gear the ratio down • Working against a lot of weight • 1:2 – one shaft revolution = two motor revolutions • Gear the ratio up • Working with less weight and quicker speed • 2:1 – two shaft revolutions = one motor revolution • Must have enough torque to pull arm and manipulator up and down • Must have enough torque to contain object that’s being manipulated

22. THANK YOU! • Beach Cities Robotics • Northrop Grumman • OCRLC • Orange Coast College • FIRST • VEX, IFI, VRC

23. CHALLENGE! Goal: Obelisk Object: Ping Pong Ball d: 2 in. 3 in. 24 ft. Objective: Score ping pong balls into obelisk Challenge: Design an arm and manipulator for this task.

24. THE END