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V E X Arms

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. Torques are large Use counterweights and gears to compensate Attach the gear to the arm Attach the motor to the robot. gear

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V E X Arms

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  1. VEX Arms Robert’s ARL robot in 2006

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

  3. 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

  4. Rotating Arm Carrier Robot posted on www.vexforum.com by VexLABS

  5. Torque (T) T = F┴d distance force perpendicular F d pivot point

  6. d1 Which arm has more torque on it? 10 lbs Arm 2 Arm 1 10 lbs d2

  7. 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

  8. Power(Two Equations) - or -

  9. 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

  10. 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

  11. Multi-Jointed Arms Put multiple sections together to increase dexterity. www.vexrobotics.com Posted on www.vexforum.com by juniorVEXbot

  12. Arms Challenge

  13. Advice • 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

  14. 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.

  15. use limit switches & stop arms mechanically mechanical stop: something the arm hits to physically stop it

  16. 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 *

  17. Potentiometers(Variable Resistors) • Resistance depends on shaft rotation • Useful to accurately measure angles • Limited range of rotation

  18. Thanks/Resources • Designing Competitive Manipulators: The Mechanics & Strategy by Greg Needel (www.robogreg.com)

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