A Wheeling-Hopping Combination Scout Robot

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976 J. Zhao et al.Fig. 3. F y -Y curve of the five-shank mechanismThus in this paper, the five-shank mechanism is adopted, and the relation between itsacting force and deformation is simplified by curve fitting method as*F y= Ky (1 −4aIn it, K , a and b are the parameters of the fitting curve. K = 5 , b = 25, a = 42. 5 weregot when it was set as k = , L = 30, L = 40, L 45 .b2− y5 0 1 2 =Assume that the length of the five-shank mechanism in direction Y is y 0 when thespring has no deformation. According to Hooke’s law, the equivalent elastic coefficientof the non-linear spring produced by the five-shank mechanism is*2( y )0).(2)K( y)= Fy − y . (3)4 Analysis on the Dynamic Model of the RobotIn order to get the jumping performance of the five-shank mechanism, it is necessaryto establish the dynamic model of the robot. At present the jumping model can bedivided into two kinds: spring-single mass continuous jumping model and springdoublemass intermittent jumping model. The former refills the energy of jumpingand adjusts the robot’s attitudes dynamically, and then goes on with the next jumpafter landing. So the continuous equation of motion can be set up for this model. Butusing this model, it is difficult for the robot to balance in quiescent condition. Also,the horizontal distance is limited because of the front rake which is hard to control, asa result the robot is always assumed to be vertical before jumping. The latter has twomass connected by a spring. The bottom mass balances and stabilizes the whole robot.After landing the robot refills energy of jumping and adjusts its attitudes according tothe circumstance, and gets ready for the next jump. This model is more practical forthe robot mentioned above.
A Wheeling-Hopping Combination Scout Robot 977The wheeling-hopping combination scout robot built in this paper stores energyfrom the extension of spring driven by the motor, which obviously belongs to intermittentjumping model. Meanwhile, the upper part of the robot is much heavier thanthe supporting leg of the five-shank mechanism, so single mass jumping model actsmore accurately for the robot. Moreover, three-point supporting composed of twowheeldriving assembly and the supporting leg balances the robot in quiescent condition,and the front rake can be adjusted by the three-point supporting to get enoughhorizontal distance. Considering all the factors above, a nonlinear spring-single massintermittent jumping model (see Fig 4) is established for the robot.Fig. 4. Jumping model of the robotr is the original length of non-linear spring, and ϕ is the front rake of robot. Thenthe five-shank mechanism is equivalent to the non-linear spring whose elastic coefficientis K (r), just as expression (3). Some processes and transients which are importantto jumping performance will be analyzed.4.1 Process on the GroundAssume that the point in which the potential energy is zero lies on the ground, thenthe kinetic energy and potential energy of the robot in the process on the ground areSo the Lagrange's equation is2 2( r!+ ( rϕ!) ),$ 1! K = M2!# V1= Mgr sin ϕ ,! 1! V2= K ( r)0" 2( r − r )2.2 21( r!+ ( rϕ!) ) − Mgr sin − K ( r)( r − r ) .1 20L = Mϕ22Substitute it into the second Lagrange's equationd * ∂L' ∂L( %− = 0.dt ) ∂x!i & ∂x i(4)
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A Wheeling-Hopping Combination Scout Robot

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