Power, Torque and Robot arms

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# Power, Torque and Robot arms - PowerPoint PPT Presentation

Power, Torque and Robot arms. An intro. V E X Arms. Robert’s ARL robot in 2006. Outline. Rotating Arms Torque Power Multi-Jointed Arms Challenge Limit Switches. counter weight. motor. Rotating Arms.

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## PowerPoint Slideshow about 'Power, Torque and Robot arms' - leandra-winters

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Presentation Transcript

An intro

### VEX Arms

Robert’s ARL robot in 2006

Outline
• Rotating Arms
• Torque
• Power
• Multi-Jointed Arms
• Challenge
• Limit Switches

counter weight

motor

Rotating Arms

Torques are largeUse counterweights and gears to compensateAttach the gear to the armAttach the motor to the robot

gear

bolted to arm

driven gear

Rotating Arm

Carrier Robot

posted on www.vexforum.com by VexLABS

Torque (T)

T = F┴d

distance

force

perpendicular

F

d

pivot point

d1

Which arm has more torque on it?

10 lbs

Arm 2

Arm 1

10 lbs

d2

D1

Which arm has more torque on it?

T = F x D

D1 > D2

- so -

T1 > T2

10 lbs

Arm 2

Arm 1

10 lbs

D2

Which arm would require a more powerful motor?

Arm 1

Arm 2

D

D

Force: 10 lbs

Rotational Velocity: 200 RPM Gear Ratio: 4 to 1

Force: 10 lbs

Rotational Velocity: 100 RPM Gear Ratio: 4 to 1

Which arm would require a more powerful motor?

Force & distance are the same so torque is the same.

Arm 2 needs a more powerful motor since its rotational velocity is greater.

Arm 1

Arm 2

D

D

Force: 10 lbs

Rotational Velocity: 200 RPM Gear Ratio: 4 to 1

Force: 10 lbs

Rotational Velocity: 100 RPM Gear Ratio: 4 to 1

Multi-Jointed Arms

Put multiple sections together to increase dexterity.

www.vexrobotics.com

Posted on www.vexforum.com by juniorVEXbot

Arms Challenge

CHALLENGES LIKE THESE ARE GOOD FOR HIGH SCHOOL STUDENTS, because they are well-specified for existing robot kits.

• In our case we work on open-ended projects, more similar to real life.
• For instance we can assume nothing when designing a humanoid robot arms.
• It is however good to be realistic about costs.
• Balance arms with counterweights
• not always possible
• Use gears to get extra torque
• not always necessary with balanced arms
• Use sensors
• limit switches to stop arms from over rotating
• potentiometers or encoders to control location
Limit Switches

Limit switches tell the robot controller when a device has gone far enough.

Software can stop the servos and motors moving the device.

use limit switches

&

stop arms mechanically

mechanical stop: something the arm hits to physically stop it

Optical Shaft Encoders
• Detects 90 ticks per shaft rotation
• Useful for measuring speeds

*Old encoders (they only have one PWM cable) can’t tell direction of rotation

*

Potentiometers(Variable Resistors)
• Resistance depends on shaft rotation
• Useful to accurately measure angles
• Limited range of rotation
Sources
• J.M. Gabrielse
• Greg Needel - Designing Competitive Manipulators: The Mechanics & Strategy

(www.robogreg.com)