Two wheels connected by an unactuated variable length axle on uneven ground: Kinematic modeling and experiments

It has been shown in previous work that when two wheels independently joine d by a fixed-length axle are placed on an uneven surface, such that the lin e joining the wheel contact points is not coplanar with the axle, rolling w ithout slip is possible only if the wheels are driven at the same speed. Ot herwise, the wheels must slip against the terrain due to kinematic constrai nts. Based on analytical kinematics, it is shown in this article that a met hod to prevent slip on uneven terrain is to use a variable length axle. Thi s research explores the instantaneous and gross motion of two wheels joined by a variable length axle on uneven terrain. Next, the overall range of th e axle length change is investigated through numerical simulations. Based o n the results from the simulation, a novel variable length axle that posses ses no prismatic joints, hence has low friction, and has high stiffness has been designed. Experimental results are obtained for the axle length chang e as a three wheeled laboratory prototype that includes the variable length axle travels on a smooth uneven surface. These experiments verify the kine matic model. Limitations of using an unactuated variable length axle and re lated future research topics are also discussed.