STEAM POWERED STEAM POWERED ROBOTSROBOTS

Presented by… Presented by…

Debasish Devkumar PadhyDebasish Devkumar Padhy

88thth sem Mechanical Engg. sem Mechanical Engg.

Contents..Contents..

IntroductionIntroductionCurrent systems of power supplyCurrent systems of power supplyA new approach (monopropellant based)A new approach (monopropellant based)How does it work?How does it work?Description of the designDescription of the designThe prototypeThe prototypeTest resultsTest resultsLimitationsLimitationsFuture of the projectFuture of the projectConclusionConclusion

Current systems of power supplyCurrent systems of power supply

Parameters governing power supply designParameters governing power supply design

Specific energy density of power supply (Es) the Specific energy density of power supply (Es) the efficiency of converting energy from the power efficiency of converting energy from the power source to controlled mechanical work the efficiency source to controlled mechanical work the efficiency of converting energy from the power source to of converting energy from the power source to controlled mechanical work(n) , and the maximum controlled mechanical work(n) , and the maximum mass-specific power density of the energy mass-specific power density of the energy conversion and/or actuation system(Ps) . conversion and/or actuation system(Ps) .

Actuation potentialActuation potential

A.P = Es*n*PA.P = Es*n*P

That a system with high power-source That a system with high power-source energy density, high conversion efficiency, energy density, high conversion efficiency, and high actuator power density will be the and high actuator power density will be the lightest possible system capable of lightest possible system capable of delivering a given amount of power and delivering a given amount of power and energy. energy.

With regard to the figure of merit, batteries and dc With regard to the figure of merit, batteries and dc motors capable of providing the requisite power for a motors capable of providing the requisite power for a human scale robot offer reasonable conversion human scale robot offer reasonable conversion efficiency, but provide relatively low power-source efficiency, but provide relatively low power-source energy density and a similarly low actuator/gear head energy density and a similarly low actuator/gear head power density. A gasoline-engine-powered hydraulically-power density. A gasoline-engine-powered hydraulically-actuated human-scale robot would provide a high power-actuated human-scale robot would provide a high power-source energy density, but a relatively low conversion source energy density, but a relatively low conversion efficiency and actuation system power density.efficiency and actuation system power density.

Monopropellant Powered ApproachMonopropellant Powered Approach

Liquid chemical fuels can provide energy densities significantly greater Liquid chemical fuels can provide energy densities significantly greater than power-comparable electrochemical batteries. The energy from these than power-comparable electrochemical batteries. The energy from these fuels, however, is released as heat, and the systems required to convert fuels, however, is released as heat, and the systems required to convert heat into controlled, actuated work heat into controlled, actuated work

One means of converting chemical energy into controlled, actuated work One means of converting chemical energy into controlled, actuated work with a simple conversion process is to utilize a liquid monopropellant to with a simple conversion process is to utilize a liquid monopropellant to generate a gas, which in turn can be utilized to power a pneumatic generate a gas, which in turn can be utilized to power a pneumatic actuation system.actuation system.

monopropellants are a class of fuels (technically propellants since monopropellants are a class of fuels (technically propellants since oxidation does not occur) that rapidly decompose (or chemically react) in oxidation does not occur) that rapidly decompose (or chemically react) in the presence of a catalytic material. Unlike combustion reactions, no the presence of a catalytic material. Unlike combustion reactions, no ignition is required, and therefore the release of power can be controlled ignition is required, and therefore the release of power can be controlled continuously and proportionally simply by controlling the flow rate of the continuously and proportionally simply by controlling the flow rate of the liquid propellant.liquid propellant.

Comparison detailsComparison details

Battery powered systemsBattery powered systemsMonopropellants have better specific Monopropellants have better specific

energy density & specific power density of energy density & specific power density of conversionconversion

Gasoline engine powered systemsGasoline engine powered systemsMonopropellants have better conversion Monopropellants have better conversion

efficiency & specific power density of efficiency & specific power density of energy conversionenergy conversion

How does it work?How does it work?

Uses decomposition of hydrogen peroxide to Uses decomposition of hydrogen peroxide to produce steamproduce steam

Steam pressurizes the reservoir (similar to Steam pressurizes the reservoir (similar to pneumatically actuated systems-difference pneumatically actuated systems-difference being absence of compressor)being absence of compressor)

Liquid peroxide stored at high pressure on Liquid peroxide stored at high pressure on decomposition gives high pressure gaseous decomposition gives high pressure gaseous productsproducts

Mechanical work is extracted from this as in Mechanical work is extracted from this as in pneumatic systempneumatic system

Schematic of monopropellant based actuation Schematic of monopropellant based actuation systemsystem

The PrototypeThe Prototype

Data obtained from experimentsData obtained from experiments

Emphasis is on the conversion efficiency Emphasis is on the conversion efficiency determination as the values of the other determination as the values of the other two parameters can be easily foundtwo parameters can be easily found

Maximum possible conversion efficiency Maximum possible conversion efficiency calculated = 39%calculated = 39%

Theoretical conversion efficiency = 16%Theoretical conversion efficiency = 16%Actual conversion efficiency obtained = Actual conversion efficiency obtained =

6.6%6.6%

Reasons for lower value of n Reasons for lower value of n

Heat loss from the systemHeat loss from the systemOvershoots or deviations from the Overshoots or deviations from the

assumed trajectory of the prototypeassumed trajectory of the prototypeInaccuracy of controlsInaccuracy of controlsOvershooting causes intermittent exhaust Overshooting causes intermittent exhaust

of hot gas causing low nof hot gas causing low n

Insulated experimentsInsulated experiments

Prototype in the previous Prototype in the previous experiment is covered with experiment is covered with insulation to reduce heat insulation to reduce heat loss and thereby improve loss and thereby improve conversion efficiencyconversion efficiency

Efficiency obtained from Efficiency obtained from experiment = 9%experiment = 9%

Reasons for efficiency lower Reasons for efficiency lower than theoretical valuethan theoretical value

Heat loss still existsHeat loss still exists Inaccuracy of controlsInaccuracy of controls

Fig. 8. Monopropellant actuator prototype wrapped with insulating tape andinstrumented with thermocouples for measurement of surface temperature.

Determination of actuation potentialDetermination of actuation potential

Actuation system mass = 1.5KgActuation system mass = 1.5KgActuation system power density=100W/KgActuation system power density=100W/KgConsidering mass of blow down tank, specific Considering mass of blow down tank, specific

energy density = 1.7 MJ/Kgenergy density = 1.7 MJ/KgFor single degree of freedom system, actuation For single degree of freedom system, actuation

potential = 15.3 KJ KW/Kg2potential = 15.3 KJ KW/Kg2For six degree of freedom system A.P=26.4 KJ For six degree of freedom system A.P=26.4 KJ

KW/Kg2KW/Kg2Actuation potential of the best battery available = Actuation potential of the best battery available =

4.8 KJ KW/Kg24.8 KJ KW/Kg2

LimitationsLimitations

High energy loss in the form of heatHigh energy loss in the form of heatAt present 100% H2O2 can’t be usedAt present 100% H2O2 can’t be usedNo human scale self powered robot available at No human scale self powered robot available at

present. The study was done on a single degree present. The study was done on a single degree of freedom manipulatorof freedom manipulator

H2O2 is a costlier power source than electricityH2O2 is a costlier power source than electricityMaintenance costs are higherMaintenance costs are higherH2O2 is less safe compared to electricityH2O2 is less safe compared to electricity

Future of the projectFuture of the project

Multiple degrees of freedom systems will give higher Multiple degrees of freedom systems will give higher actuation potentialactuation potential

Better insulation can prevent heat lossBetter insulation can prevent heat loss 100% H2O2 if used would increase actuation potential100% H2O2 if used would increase actuation potential 100 % H2O2 systems provides actuation potentials 35 & 100 % H2O2 systems provides actuation potentials 35 &

60.4 for single and six degrees of freedom respectively60.4 for single and six degrees of freedom respectively Better controls can contribute to improved conversion Better controls can contribute to improved conversion

efficiencyefficiency Light weight components and heat resistant materials Light weight components and heat resistant materials

can make this technology a promising option in the can make this technology a promising option in the futurefuture

ReferencesReferences

IEEE/ASME transactions on Mechatronics, vol. IEEE/ASME transactions on Mechatronics, vol. 8, no. 2, June 20038, no. 2, June 2003

New Scientist, 27 April 2002New Scientist, 27 April 2002www.qrg.northwestern.edu/projects/ www.qrg.northwestern.edu/projects/

vss/docs/Propulsion/3-what-is-a-vss/docs/Propulsion/3-what-is-a-monopropellant.html monopropellant.html

www.daviddarling.info/ www.daviddarling.info/ encyclopedia/M/monopropellant.htmlencyclopedia/M/monopropellant.html

www.stormingmedia.us/41/4193/A419314.html www.stormingmedia.us/41/4193/A419314.html http://en.wikipedia.org/wiki/Hydrogen_peroxidehttp://en.wikipedia.org/wiki/Hydrogen_peroxide

ConclusionConclusion

A power supply and actuation system appropriate for a position or force controlled human-scale robot was proposed.

The proposed approach utilizes a monopropellant as a gas generant to power pneumatic-type hot gas actuators.

Experiments were performed that characterize the energetic behavior of the proposed system and offer the promise of an order-of-magnitude improvement in actuation potential relative to a battery-powered dc-motor-actuated approach.

THANK YOUTHANK YOU

Debasish Devkumar PadhyDebasish Devkumar Padhy

MECHANICAL ENGG.MECHANICAL ENGG.