FTC Manipulators

By: Zach Zakfeld (Enigma Robotics)

Teams: FTC 5391, FTC 5385 and FRC 2075

*Some images in this presentation are of FRC robots so exact designs may not be applicable, however all of the principles are still valid.

Manipulators

• Basic/Background Info

• Types of Manipulators

• General Manipulator design tips

Background Info

• Manipulator: Anything that interacts with a scoring element, field element, or game piece

• Intake: Mechanism that moves the game piece from the field onto the robot

• Usually, an intake is combined with some mechanism that moves the game piece around to be scored.• Pivot Arm

• 4-Bar Linkage

• Lifts (Sliding/Telescoping)

• Shooter

Intake

• Often the most important part of the robot.

• Determines how quickly game pieces can enter, and often times leave the robot.

• Often times game pieces do not ever leave the intake until they are scored.

• Often put onto the end of an arm or lift to move game pieces

• Effective intakes should:• Have high range of acceptance• Be quick• Be forgiving• Be breakdown free• Work efficiently with the rest of the robot design

Types of Intake

• Claw/pincher: used when something needs to be grabbed or pinched

• Had some kind of grabbing or pinching motion to secure game piece

• Roller Claw: used in the same manner as a normal claw or pincher

• Has motorized rollers to “suck” the game piece in.

Types of Intakes

• Collectors: Used when multiple game pieces want to be collected at the same time, or when the game piece will be scored by a mechanism other than the intake.

• Often a bar that can fold out of robot with “fingers” to pull game pieces into robot.

• Then either stored in carriage that collector is attached to or moved to a different part of the robot to be scored.

• Most often used when multiple game pieces are desired to be scored at once.

• Passive intakes: Used usually only as a last resort

• No powered mechanism to collect game pieces

• Can consist of a funnel to gather game piece into desired location

• Requires robot to drive into EXACT position for game piece to be picked up.

• NOT RECOMMENDED unless it is a last resort situation.

Pivot Arm

• Arm whose shoulder is a simple pin or axle pivot point.

• Most often used in conjunction with a “wrist” to get the game piece and intake into the correct orientation.

• Can be used in conjunction with an “elbow” (also called a 2-stage arm) but adds complexity to design and operation

• Most often the power supplied through a gear or sprocket fixed to the arm• Can also be done with linear motion attached to the middle or closer to the

end of the arm (leverage)• Not recommended to run arm past pivot point and attach string to “pull” arm

up

4-Bar Linkage

• 4 Bars combined to make the carriage or hand stay level at all times.

• Simplifies tasks where carriage needs to stay level by eliminating need for “wrist”

• Very stable in all directions

• Most often powered by linear motion device attached to middle/end of arm.

• Can also be powered by sprocket or gear attached to arm rotating around either pivot point of arm.

Pivot Arm VS 4-Bar Linkage Arm

• 4-Bar Linkage• Stable in all directions of force

• Maintains level Carriage

• More difficult to make “elbow” for extending past length of arm

• Takes up more space on the robot

• Only approximately 130 degrees of rotation (depends on distance between pivot points

• Pivot Arm• Only stable to force parallel to axis

if two bars are used.

• Carriage rotates with arm

• Easier to make an elbow to extend reach of the arm

• More compact on robot

• Full 360 degrees of rotation

Arm Tips and Tricks

• Using a linear force mechanism to push and pull the arm gives the advantage of leverage

• Sometimes an elbow is needed to extend range. Consider creating a snap-lock mechanism to lock arm in place once the arm is extended to desired position.

• Arms can be geared for VERY high torque and still maintain speed because it takes less than one rotation of axle to extend to full position.

• Encoders mounted to motor output shaft or any shaft between motor and pivot axle can be used to give more accurate encoder readings.

• Inconsistent Forces during lift can be utilized for an advantage

• Spring assists can reduce stress on motor and allow for less gearing

Telescoping Lifts

• Different sized, concentric tubes (square or round) that extend out of each other.

• Usually driven by a string wrapped around a drum

• Recommended that some kind of cable tensioning system is used to avoid tangles in the event of a jam

• Not recommended for heavy loads.

• Cascading vs Continuous lifting

• Recommended to use Teflon or other low

friction material where the tubes will overlap

and especially where they will pinch.

Sliding Lift

• Bars that slide up and down on each other with rollers that support carriage on both sides

• Usually driven by a chain that runs up and down each bar on the lift.

• Because each bar is supported on both sides it can support heavy loads

• If not driven by one continuous chain, recommended that it is still driven both up and down to avoid jams

• Cascading vs Continuous lifts

Sliding VS Telescoping Lift

• Sliding Lift• Can support heavy loads without

pinching or binding

• Takes up extra space in robot for each stage

• Carriage can slide up last stage on lift, may be independently if needed

• Telescoping Lift• Does not support heavy loads

efficiently

• Total size is only the size of the largest tube, adding stages does not directly mean making it larger

• Carriage must be in fixed position on last stage of lift

Lift Tips and Tricks

• Lifts that are powered both up and down allow for the ability to overcome binding and friction

• Both sliding and telescoping lift techniques can be used for vertical as well as horizontal travel

• Standard cabinet drawer slides are COTS parts that make excellent slides for FTC applications

• Spring assist can allow for much increased speed while maintaining ability to lift heavy objects

Shooter*I have not been involvded in a game where a shooter would be beneficial for FTC

• Flywheel• Gives object momentum by using

a rapidly spinning, heavy wheel

• Similar to a automatic pitching machine

• Very fast

• Applies spin to object

• Single Flywheel shooter

• Multi Flywheel shooter

• Curved path flywheel shooter

• Catapult• Gives object momentum by

flinging it

• Slow, must be individually loaded between each shot

• Does not necessarily apply spin

• Motor powered Catapult

• Spring Loaded Catapult• Lock and Release

• Cam system

General Manipulator Tips and Tricks

• Using encoders to automate repeated tasks is highly recommended

• Mechanical Assists whenever possible allow for less stress on motors and prolonged consistent behavior

• Mechanical Brakes allow for Arms and lifts to not back drive• Ratchets: completely lock in one direction, must be released to go in reverse

direction, can only lock in set intervals

• Clutch Bearing: Completely lock in one direction, can lock at exactly any position

• Brake Pads: Stop motion in both directions at any point. Apply friction to either chain, gear or wheel

• Motor Braking: Applies load to motor, not held once power to motor is lost, not recommended to be used for safety measure or to hold position at end of game.