Manipulators By: Zach Zakfeld (Enigma Robotics) Teams: FTC 5391, - - PowerPoint PPT Presentation

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

• r 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
• ther.
• 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
• n last stage of lift

Lift Tips and Tricks

• Lifts that are powered both up and down allow for the ability to
• vercome 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.