A Wheeling-Hopping Combination Scout Robot

More documents

Recommendations

Info

978 J. Zhao et al.After simplification, differential motion equations of the robot are$2M ⋅!!r − M ⋅ r ! ϕ + Mg sinϕ− K ( r)!# 2d( Mr ! ϕ)! + Mgr cosϕ= 0." dt( r − r)0= 0,With the consideration of the fact that the inertial rotation hardly functions on themovement because of the attitude adjusting, it is supposed that the robot neglects itsinertial rotation and the ϕ is a constant. So the equation (5) can be simplified intoM ⋅ r!! + Mg sin ϕ + K ( r )( r − r0 ) = 0.If ω 2 = K ( r ) M , the initial condition is r ( 0) = r0( r 0 is the original length of nonlinearspring), r! ( 0) = 0. After the differential equation is solved, expression of the robot’smotion during the process on the ground is* K ( r ) L 0 g sin ϕ 'r ( t ) = (− % sin ( ω t ) + r0cos ( ω t ).(6)) ω M ω &(5)4.2 Jumping TransientAssume that the robot doesn’t jump beforehand, the robot in jumping transient satisfiesthe criteriar ( t′ ) = r0, r! ( t′ ) > 0.A function is introducedr*( r − r ) dr − Mg ( r * −r) sin ϕ .Θ ( r*,r0, ϕ , M , K ) =+K ( r ) 00r0In it r * − r0is the deformation of non-linear spring, and ϕ is the front rake of therobot.WhenF y = Mg sin ϕ , in Fig 3 there are two corresponding points ( F y , r 1 )F y, and r 1 < r2. When r* ∈ ( r 1 , r 2 ), the five-shank mechanism can offer lar-and ( ) , r 2ger force than the weight of the robot, so the jumping criteria is$ Θ(r*,r0, ϕ,M , K ) > 0,#" r1< r*< r2.If viscous damper and friction are ignored, the energy conservation equation isr ∗+r01K ( r ) 0022( r − r ) dr = M ( v *) + Mg ( r * − r ) sin ϕ .In it, v * is the initial off-ground velocity, and r * is the length of the five-shankmechanism in Y direction when off-ground4.3 Aerial ProcessAfter jumping over, the robot is in parabolic motion under the effect of its ownweight, so the equation of motion for the robot is(7)
A Wheeling-Hopping Combination Scout Robot 979$ ∗ 1 2! Y ( t)= v t sinϕ− gt + r0sinϕ,#2! ∗" Z ( t)= v t cosϕ.(8)4.4 Jumping HeightUnder the condition that the efficiency is ignored, the robot can move to the highestpoint when all its elastic potential energy turns into gravitational potential energy. ItsatisfiesMg2( H r *) = K ( r )( r − r ) dr − M ( v * cos ϕ ) .maxr ∗−+So the maximum jumping height of the robot is:r0012(9)Hmax1 r ∗20= K ( r )Mg +r012 g( r − r ) dr − ( v * cos ϕ ) + r * .(10)The maximum jumping height H is the most important parameter of the wheelinghoppingcombination scout robot. According to expression (10), it closely relates tomaxthe initial off-ground velocity v * , the length of the five-shank mechanism in Y directionr * , and the front rake of robot ϕ .The front rake ϕ is determined by the comprehensive requirements for both jumpingheight and horizontal distance. According to jumping criteria of expression (7), itis necessary to make r * be close to r 2in order to get a higher jumping height. At thesame time, an initial velocity is needed to avoid the robot jumping beforehand. So anelastic buffer set in the five-shank mechanism with the thickness of r2 − r3is designedto absorb the deformation from r 2to r 3in direction Y. And then, just as thefive-shank mechanism gets r 3, the robot gains the largest Fmaxto jump over. Thusthere are larger impact force and jumping velocity for the robot to get an ideal height.5 Simulation Analysis and Jumping Experiment of the RobotA simulation analysis is carried out with the software ADAMS to validate the jumpingperformance of the robot. The parameters of the spring are as follows: the elasticcoefficient of spring k = 5N/mm , the damping of the spring C = 0.05Ns/mm, the0original length of the spring L 0 = 30mm , and the front rake of robotϕ= 60 . Thenthe height-time curve of robot’s barycenter is shown in Fig 5.From Fig 5 we can see that the maximum jumping height of the robot is about150mm. From equation (10) we got theoretical maximum jumping height, 180mm,which is close to the simulation value.In the jumping experiment, when four springs with elastic coefficientk = 1.2N/mm are used for the five-shank mechanism, the maximum jumping height of
Page 2 and 3: 974 J. Zhao et al.2 Brief Account o
Page 4 and 5: 976 J. Zhao et al.Fig. 3. F y -Y cu
Page 8 and 9: 980 J. Zhao et al.Fig. 5. The heigh

A Wheeling-Hopping Combination Scout Robot

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?