Research On Lunar Terrain Trafficability Of Lunar Rover Of Rocker And Bogie

There is much big difference between moon and earth,such as temperature,rang of temperature varying,gravity and vacuum.The lunar rover will be lunched in second stage of moon exploration of china.Surviving on the moon is first thing for lunar rover.The second thing is to cruise on the moon.So one of the most important questions is lunar terrain trafficability for lunar rover.The lunar rovers of former Soviet Union and America ever sank deeply in lunar soil and exploration plan were changed because lunar terrain trafficability of lunar rover was poor.Yrafficability of lunar rover includes trafficability of wheel supporting, geometric trafficability on tough lunar terrain and capability of climbing obstacle. This paper researches on driving force of wheel on lunar soil,the criterion of selecting wheel dimension,geometric trafficability on tough lunar terrain,the driving force optimization of wheel for moving safely on the moon,capability of climbing obstacle. The details are following:1.Analysis on the characteristic of lunar rover of rocker and bogie.Now researchers who make researches on mobile system of lunar rover mostly focus on chassis suspension mechanism,joint mobile mechanism,shape shifting mobile mechanism and rocker and bogie mechanism.All of these,the rocker and bogie mechanism is best. It has simple structure,the ability to adapt tough terrain,narrow range of wheel supporting force varying and good capability of climbing obstacle.Contact angle is an important parameter for lunar rover of rocker.and bogie.It affects the wheel force distributing of lunar rover.The formula of calculating contact angle was gained based on velocity projection theorem in this paper.It will be used in optimization of force driving of wheel.2.Driving force of wheel on soft lunar soil is much different with wheel on the ground of the earth.Wheel sinks and slides easily on lunar soil.The driving force formula of wheel based on Bekker formula is much complex,for forecasting driving force,curve fitting based on least squares method was introduced to simplify formula driving force.The driving force can be calculated through measuring wheel sinkage and slide.The diameter and width of wheel decide the trafficability of lunar rover on tough lunar terrain.The criterion of selecting dimension of wheel was developed with a view of wheel sinkage,driving force and driving efficiency. 3.Experiments of wheel driving force.The experiment system of driving force was established for testing driving force characteristics of wheel moving on soft soil which force characteristics is similar to lunar soil.The parameters which were measured in driving force experiment include velocity of driving motor,velocity of wheel and wheel sinkage.These parameters can be calculated to derivate driving force of wheel. The difference between actual driving force of wheel and driving force of calculation was compared and the range of wheel dimension was recommended.Increasing slide can decrease efficiency of wheel driving though driving force can be increased through increasing slide.In experiments,grousers were added to wheel surface to increase driving force of wheel.Grousers can increase driving force of wheel.Yet grousers also introduce vertical wave of wheel.It is disadvantageous to stability of lunar rover.The frequency of wheel wave is a function of velocity of wheel motor, dimension of wheel,density of grousers and wheel slide.The formula of frequency of wheel wave was derivated in this paper.It is a criterion of avoiding sympathetic vibration of lunar rover.4.Geometric trafficability on tough lunar terrain.Every wheel of lunar rover of rocker and bogie has an own driving system.The contact angles of wheels on tough lunar terrain are different.So considering trafficability of every single wheel isn't circumspect.If driving force of wheels are not concerted,it will happen that some wheel sinks and can't produce driving force since wheel sinks too deeply.So cooperative controlling of driving force of wheel is a key of trafficability on tough lunar terrain.Based on SQP algorithm,driving force of wheel was optimized. Optimization is based on restriction of moving safely and smoothly.The aim of optimization is to minimize power consume of motors and varying range of driving force.It is important for lunar rover which power is limited.Dynamic equation of Lagrange was established.It was simulated that lunar rover moves on tough terrain moon.And optimization results of wheel driving force were derivated through Matlab software.5.Analysis on capability of climbing obstacle.The lunar rover of rocker and bogie must has good capability of climbing obstacle and adaptive for tough lunar terrain. The dimension of rocker and bogie mechanism was determined according to lunar terrain and design of climbing obstacle.The body of lunar rover has different position of gravity when arrangement of instrumentation in body is different.The position of gravity affects capability of climbing obstacle;improper position of gravity center depresses climbing obstacle capability.The feasible range of gravity center was found out through quasi-static analysis.