Agenda Project Recap/Proposed Design Updated Engineering Specs Customer Needs System Connections & Interactions McKibben Air Muscle Testing Air Supply Selection Power Supply Selection Logic Selection & Implementation Shell/Covering Design: Aesthetics CAD Model Model Analysis Bill of Materials Risk Assessment Test Plan MSDII Schedule
Project Recap/Mission Statement The project goal is to create a robot that mimics a jumping tiger both dynamically and to a lesser extent, aesthetically The jumping force is to be provided by air muscles
Customer Needs Customer Need Importance (1 = high)Description CN11 Can jump forward a distance equal to at least the length of its body (only 1 jump required per tank fill) CN21Use air muscles to provide jumping force CN31Lands safely without damage CN42 Is ready to jump again after landing, without user adjustment of robot body or legs CN52Self-contained (on board power sources) CN62Portable (small enough for one person to carry) CN72 Reasonable battery life; battery charging takes hours CN83Resemble a tiger CN93Controls do not yield a noticeable delay
Proposed Design: Completely self contained robotic tiger On board air supply, power supply, controls, & muscles Utilizes McKibben Air Muscles to create jumping motion Patterned attachment holes in legs to allow for air muscle testing and adjustability Air release controlled using an Arduino Board and sprinkler valves Rechargeable power & refillable PVC pressure chamber
Specifications SpecSourceMetric Unit of MeasureMarginal ValueIdeal Value Preferred Direction S1CN1Horizontal Jump DistanceFeet1*body length1.5*body lengthUp S2CN1,2Uses Air Muscles Binary Yes S3CN3Sliding Distance After LandingInches 3 2Down S4CN4,5Self-Contained Binary Yes S5CN3,6Overall WeightLbs5025 Down S6CN3,5,6Overall LengthFeet42Down S7CN3,5,6Overall HeightFeet21Down S8CN3,5,6Overall WidthFeet1 Down S9CN8Resemble a Tiger Percent80 100Up S10CN2Regulated Air Pressurepsi<100 60Down S12CN9Total Response Time to Jump Commands0.30.15Down S13CN2,9Solenoid Response Timems5025Down S14CN2,9Muscle Fill Times.5.25Down S15CN2,7Battery Life# of Jumps1100Up S16CN2,8Two Actuated LegsBinary Yes S17CN4,5Tank can be filled in less than 5 minutesBinary Yes
System Connections Battery/Tether Power Runs Compressor Air Energy from compressor is stored in tanks Pressure energy is converted into motion Air Muscles and Cables Moves hind legs for jumping action Leg Mechanism function simultaneously for Jumping motion Control system Designed for system (Lab View) Sends a Output through Wireless transmitter Output Changes the state of the Solenoid Valves Tiger Jumps Forward
Air Muscles Rubber tube inside of a braided mesh sleeve Pressurized tube inflates causing the mesh to contract in length Closely mimics biological muscles
Pressure Chamber Design Topics of concern Flow Rate Currently the muscles fill to slowly to lift the robot from off the ground. Force during contraction Currently we are able to achieve a maximum force of about 30lb per air muscle. However the force during the contraction is much lower resulting in slow weak movements. Bottlenecking This occurs at all the current joints where air is flowing and is impacted by the smallest inner diameter of the first connection currently this is the solenoid. (shown on the left) Even with larger port sizes (3/8” shown) for fittings the valve inlet and outlet is small (yellow) and restricts flow.
Proposed solution Design to overcome obstacles Use high flow rate valves The current solenoid valves shown on the previous slide do not have good flow rate as demonstrated in the YouTube videos. The solution to this issue is the use of sprinkler valves, they are rated for the pressure required and the offer very high flow rate. This high flow rate will help achieve a faster muscle fill and cause the robot to jump.
Proposed Solution Design to overcome obstacles Use larger fittings The current muscle fittings have a small port ID and will need to be increased to allow the muscle to fill at a faster rate.
Proposed solution Design to overcome obstacles Change the pressure chamber Safety??? The current use of a 3000 psi pressure chamber with 60 psi regulator while good for previous air muscle projects limits the flow rate of the air leaving the chamber. The proposed solution utilizes a lower 20-120 Psi chamber that will allow a greater flow rate leaving the nozzle. Pressure chamber Valve location Fill location This Pressure chamber was designed with the use of a very rough calculation to check the final muscle pressure in the muscles was optimal while the pressure in the tank was set to 60Psi.
Controls Selection What we are planning to use: Arduino Mega 2560 Simple programming language 54 channel capability Fully autonomous Cost effective (existing part)
Power Supply 9V battery to power Arduino board 2000mAh 24V NiMH battery to power sprinkler valve solenoids Heavy but free Solenoids Draw 400mA for 1 sec to hold valve open, each At 20 jumps per hour, battery lasts 300 hrs
Solenoid Control Board Provides signal from the microcontroller to the solenoid valve for muscle actuation. There will be one iteration of this circuit per solenoid used to control muscle contraction order.
Jump Logic Power On Reset Muscle Positions to normal Wait for Go Input Command Return Go? No Contract muscle Group 1 Yes Contract muscle Group 2 Contract muscle Group 3 Wait Release muscles
Continued air muscle testing was preformed (different way of mounting air muscles tested; hooks on the fitting vs mesh loop used) Pre-compressing the mesh and stretching the muscles to get a bit more deflection Wooden leg built for project feasibility testing Attaching multiple muscles to a leg to get more force https://www.youtube.com/watch?v=_ObyHcskls w Testing
Wooden leg Prototype https://www.youtube.com/watch?v=1i3mJSSaIqI https://www.youtube.com/watch?v=qq48kK5-Li4 https://www.youtube.com/watch?v=5hcW5bUXf6k Problems Encountered and things we Learned: Need for Tension on muscles for movement to occur Need for weight on upper body link Lack of a stop for the upper body link Unable to launch with stability with only one leg Leg needs to be angled in order to jump desired way No way to return to home position yet Could be improved with faster firing muscles (large orifice size)
Mass Properties Weight Analysis Assembly with PVC system 2-tanks ~ 18 lb PVC system 2-tanks ~ 5 lb Hind Leg Assembly ~ 1 lb x2 Front Leg Assembly ~.8 lb x2 80/20 Body ~ 10 lb This picture shows the center of mass as calculated by SolidWorks 2012.
Body Design Body Design Merits Strong Adjustable Easily test multiple configurations Light Weight No Machining
Leg Design General Design Merits Adjustable Muscle anchor points Hard stops Pivot points Simple Easily Manufactured Cheap Versatile Ability to test and idealize multiple configurations Light Weight
Leg Design Cont. Pivot Points Rod and Shaft Collar Design Cheap Proof of concept – prototype Main Body – Leg Connector Fork Style Holster Simple Proof of concept – prototype Rod and Shaft Collar
Leg Design Cont. Leg Dimensions General Location ID #Length (in.)Width (in.)Thickness (in.) Plates in Parallel (y/n) Hind Legs 11610.25n 21610.125y 31210.25n Front Legs 41210.25n 5410.125y 6810.25n
This picture is meant to be a visualization of our current idea for muscle ( ) and spring ( ) placement. Hind Leg Design Function Extension Needs to extend with enough force to lift robot off ground Air muscles in lever configuration Retraction Springs Need to bring legs back but not interfere with extension to extensively
Jump Dynamics Simulation of take off Reinforced the need for hard stops on legs Inputs Joint moments Lengths Masses/CM locations Initial Angles Outputs IC’s for free flight
Jump Dynamics Future – implement series of event detections Fix each link when it reaches 45° Remove the ground constraints at each foot when the normal force is zero
Free Flight Dynamics Simulation models free flight of tiger IC’s needed Angles and rate of change Position of foot Uses Test different setups Find spring force needed for return
Free Flight Dynamics Inputs Spring coefficient Damping coefficients Centers of mass Masses Lengths Outputs Distance traveled Animation/ positioning Time for joint return
Free Flight Animation Future work Adjust system parameters Event detection Receive IC’s from jump program
Bill of Materials Air Supply/Connections Material/ItemOfficial NameQTY Unit Cost Total CostSourceDescription/Part Number Sprinkler Valves 4 $ 12.00 $ 48.00 Global Industrial T9FB735613 sold in sets of 2 Manifolds $ - On Hand Mesh $ 10.00 On Hand/TBD Muscle Tube 10ft $ 7.11 $ 71.10Mcmastercarr 5236K531 conservative estimate Air Hose $ - On Hand/TBDUsed to connect muscles to manifold Air Fittings $ - $ 40.00On Hand/TBDTank to manifold connections PVC $ - On HandAlready purchased for proof of concept Body Construction Frame80/20 $ - Dr. Gomes14 feet LegAluminum Sheet 1/4"2 $ 16.02 $ 32.04Mcmastercarr8975K24 6'x1' LegAluminum Sheet 1/8"2 $ 9.97 $ 19.94Mcmastercarr8975K17 6'x1" Lexan 1 $ 28.08 Mcmastercarr8560K355 1'x2' Shaft Collars 20 $ 0.84 $ 16.80McmastercarrTrevor Power and Controls Batteries24V 2000 mAhr NiMH Battery1 $ - On HandExisting battery pack from previous projects Charger Tenergy Smart Charger 12-24 V1 $ - On HandExisting charger from previous projects ArduinoArduino Mega 25601 $ - On HandMouser 782-A000047 Wiring $ - On HandVarious elctronic connections and wires Relay Parts $ - On HandLegacy parts Total $ 265.96
Further air muscle testing Looking for faster fill times Deflection and Force for bigger tube and mesh size Larger Impulse Testing with pressure vessel design Testing full build prototype Test Plan For MSDS II