Power Torque and Robot arms An intro VEX

Power, Torque and Robot arms An intro

VEX Arms Robert’s ARL robot in 2006

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

Rotating Arms gear Torques are large Use counterweights and gears to compensate bolted to arm Attach the motor to the robot motor Attach the gear to the arm driven gear cou n wei ter ght

Rotating Arm Carrier Robot posted on www. vexforum. com by Vex. LABS

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

Which arm has more torque on it? 10 lbs Arm 2 Arm 1 10 lbs d 1 d 2

Which arm has more torque on it? T=Fx. D D 1 > D 2 10 lbs - so Arm 2 T 1 > T 2 Arm 1 10 lbs D 1 D 2

Two Equations for Power - or -

Which arm would require a more powerful motor? Arm 1 D Force: 10 lbs Rotational Velocity: 100 RPM Gear Ratio: 4 to 1 Arm 2 D Force: 10 lbs Rotational Velocity: 200 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 D Force: 10 lbs Rotational Velocity: 100 RPM Gear Ratio: 4 to 1 Arm 2 D Force: 10 lbs Rotational Velocity: 200 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 junior. VEXbot

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.

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

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