Steam powered robots
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The document presents a monopropellant-based approach for powering steam-powered robots. It discusses how monopropellants can provide higher energy density than batteries. The approach uses hydrogen peroxide decomposition to produce steam for pressurizing reservoirs and powering actuators. Experiments on a prototype actuator showed a maximum conversion efficiency of 6.6%, which was limited by heat losses. Insulation improved the efficiency to 9%. The approach offers higher actuation potential than battery-powered systems but has limitations including heat losses, cost, and safety issues. Further development could improve performance and make monopropellant systems a viable option for powering robots.
Steam powered robots
- 1. STEAM POWERED ROBOTS Presented by… Debasish Devkumar Padhy 8 th sem Mechanical Engg.
- 2. Contents.. Introduction Current systems of power supply A new approach (monopropellant based) How does it work? Description of the design The prototype Test results Limitations Future of the project Conclusion
- 3. Current systems of power supply Parameters governing power supply design Specific energy density of power supply (Es) the efficiency of converting energy from the power source to controlled mechanical work the efficiency of converting energy from the power source to controlled mechanical work(n) , and the maximum mass-specific power density of the energy conversion and/or actuation system(Ps) .
- 4. Actuation potential A.P = Es*n*P That a system with high power-source energy density, high conversion efficiency, and high actuator power density will be the lightest possible system capable of delivering a given amount of power and energy.
- 5. With regard to the figure of merit, batteries and dc motors capable of providing the requisite power for a human scale robot offer reasonable conversion efficiency, but provide relatively low power-source energy density and a similarly low actuator/gear head power density. A gasoline-engine-powered hydraulically-actuated human-scale robot would provide a high power-source energy density, but a relatively low conversion efficiency and actuation system power density.
- 6. Monopropellant Powered Approach Liquid chemical fuels can provide energy densities significantly greater than power-comparable electrochemical batteries. The energy from these fuels, however, is released as heat, and the systems required to convert heat 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 generate a gas, which in turn can be utilized to power a pneumatic actuation system. monopropellants are a class of fuels (technically propellants since oxidation does not occur) that rapidly decompose (or chemically react) in the presence of a catalytic material. Unlike combustion reactions, no ignition is required, and therefore the release of power can be controlled continuously and proportionally simply by controlling the flow rate of the liquid propellant.
- 7. Comparison details Battery powered systems Monopropellants have better specific energy density & specific power density of conversion Gasoline engine powered systems Monopropellants have better conversion efficiency & specific power density of energy conversion
- 8. How does it work? Uses decomposition of hydrogen peroxide to produce steam Steam pressurizes the reservoir (similar to pneumatically actuated systems-difference being absence of compressor) Liquid peroxide stored at high pressure on decomposition gives high pressure gaseous products Mechanical work is extracted from this as in pneumatic system
- 9. Schematic of monopropellant based actuation system
- 10. The Prototype
- 11. Data obtained from experiments Emphasis is on the conversion efficiency determination as the values of the other two parameters can be easily found Maximum possible conversion efficiency calculated = 39% Theoretical conversion efficiency = 16% Actual conversion efficiency obtained = 6.6%
- 12. Reasons for lower value of n Heat loss from the system Overshoots or deviations from the assumed trajectory of the prototype Inaccuracy of controls Overshooting causes intermittent exhaust of hot gas causing low n
- 13. Insulated experiments Prototype in the previous experiment is covered with insulation to reduce heat loss and thereby improve conversion efficiency Efficiency obtained from experiment = 9% Reasons for efficiency lower than theoretical value Heat loss still exists Inaccuracy of controls Fig. 8. Monopropellant actuator prototype wrapped with insulating tape and instrumented with thermocouples for measurement of surface temperature.
- 14. Determination of actuation potential Actuation system mass = 1.5Kg Actuation system power density=100W/Kg Considering mass of blow down tank, specific energy density = 1.7 MJ/Kg For single degree of freedom system, actuation potential = 15.3 KJ KW/Kg2 For six degree of freedom system A.P=26.4 KJ KW/Kg2 Actuation potential of the best battery available = 4.8 KJ KW/Kg2
- 15. Limitations High energy loss in the form of heat At present 100% H2O2 can’t be used No human scale self powered robot available at present. The study was done on a single degree of freedom manipulator H2O2 is a costlier power source than electricity Maintenance costs are higher H2O2 is less safe compared to electricity
- 16. Future of the project Multiple degrees of freedom systems will give higher actuation potential Better insulation can prevent heat loss 100% H2O2 if used would increase actuation potential 100 % H2O2 systems provides actuation potentials 35 & 60.4 for single and six degrees of freedom respectively Better controls can contribute to improved conversion efficiency Light weight components and heat resistant materials can make this technology a promising option in the future
- 17. References IEEE/ASME transactions on Mechatronics, vol. 8, no. 2, June 2003 New Scientist, 27 April 2002 www.qrg.northwestern.edu/projects/ vss/docs/Propulsion/3-what-is-a-monopropellant.html www.daviddarling.info/ encyclopedia/M/monopropellant.html www.stormingmedia.us/41/4193/A419314.html http://en.wikipedia.org/wiki/Hydrogen_peroxide
- 18. Conclusion 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.
- 19. THANK YOU Debasish Devkumar Padhy MECHANICAL ENGG.