YA's Blog

A Three-wheeled omnidirectional robot is capable to moving in any given direction without rotating by giving velocities to the three wheels in a certain ratio. All motors are situated at an angle of 120 degrees from each other. f B ,  f L ,  f R  are for back , left and right wheel respectively. a x  and a y  are accelerations in X R  and Y R  axis in Robot frame and w is the angular velocity in Robot frame. Hence putting the values of alpha and making it into a matrix form we get : As we need to obtain the f values, we will invert the matrix. We need  a x  , a y  and w is the world frame, so we apply transformation. The transformation angle is    α 1  = 30 degrees.  Putting this in the previous equation, Multiplying the two matrices, we get the final relation as : For example, if you want to move the robot along X axis(world frame), put  a x W  = 1 , a y W  = 0 , w = 0 You will get the ratio of velocities as : 1 : -2 : 1 .

Today, my package got added to the ROS package index (list of all ROS packages). teleop_keyboard_omni3 lets you control a three-wheeled omnidirectional robot using keyboard keys. The Package summary can be found here :  http://wiki.ros.org/teleop_keyboard_omni3 (Installation, launch and usage are included in the ROS Wiki.)