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FLUID POWER! TODAY • Learn some fluid power basics • Hands-on project with pneumatic components • Some possibilities for your FIRST robot What is fluid power? • Uses: • • • • Heavy equipment Construction industry Off-road vehicles Manufacturing WHY FLUID POWER? STRONG! LIGHT! EASY! Fluid Power is Unique Unparalleled torque, power and bandwidth for the same weight or volume. Example: Power/Weight (kW/kg) Pneumatic Motor 0.3-0.4 Hydraulic Motor 0.5-1.0 Electric Motor 0.03-0.1 Fluid power weight advantage = 10:1 Reference: I. L. Krivts and G. V. Krejnin, Pneumatic Actuating Systems for Automatic Equipment, Taylor and Francis, 2006. CCEFP CENTER FOR COMPACT AND EFFICIENT FLUID POWER •100 mpg automobile •Efficient off-road equipment •Compact and portable CCEFP CCEFP testbeds TB1: Excavator TB2*: Injection molding machine Existing FP applications FP enabled breakthroughs in transportation TB3: small Urban Vehicle (sUV) TB5*: FP assisted hand tools TB4: Compact Rescue Crawler * Reduced or delayed funding CCEFP New industries & applications TB6: FP assisted orthoses & prostheses Master Pneumatic National Tube Supply Company Ralph Rivera HIGH COUNTRY TEK Member of the Schaeffler Group Pneumatics compared to hydraulics • No problems of a spills • Compressibility stores energy – Available for your use – Dangerous if excessive volumes or pressures • Difficult to control precisely • Fluid is readily available – Should be filtered, dry • Usually lower forces Safety Must Always Be Considered! Pressure of an “ideal” Gas Pressure P P V mR T • Pressure of a gas is due to the force of gas molecules bouncing off the walls. • Pressure increases when molecules are moving faster, heavier, or if there are more molecules. • Molecules move faster when they are hot. • mR depends on molecule. Getting Work out of Air • Work is force acting over a distance, ftlbs. • Put air in a container under pressure • Allow part of the container to expand • The expanding part does work How much energy is in a tank filled with compressed air? Assume constant temperature: PV mRT constant Energy: E PV ln(P / Patm ) P = pressure in tank (absolute) V = volume of tank Patm= atmospheric pressure = 101,325 Pa or 14.7 psi How much energy is in a small air tank? • Tank Volume = 150 ml or 9.154 in3 • Pressure = 413,700 Pa or 60 psi (over Patm) • Patm = 101,325 Pa or 14.7 psi Answer: Energy = PV ln(P/Patm) = 0.15 x 515025 x ln(74.7/14.7) = 125 kJ Challenge question: How high could the instructor be lifted using the energy in one tank? How much energy in your tank can you use? • Line losses: Pressure drop proportional to flow • Throttling losses: Pressure drop proportional to flow squared • Cylinder friction: Coulomb plus viscous friction, depends on seals Force available • Pressure x Area = Force • Area = pi x Bore2 / 4 • For example cylinder: – Bore = 10 mm = .394 in. Area = .122 in2 – Force = PxA = 60 psi x .122 in2 = 7 lbs Pressure P Area AP Force F CYLINDER FORCE AT 60 PSI 800 700 fORCE (LBS) 600 500 400 300 200 100 0 0 1 2 3 BORE (IN.) 4 5 The Effect of Different Areas Pressure P Area AR Area AP Pressure P How much force F is necessary to hold the rod still? Force F Pressure Patmosphere Pneumatic components seen in the FIRST Robotics competition LET'S BUILD!