Differential drive with two "cart-type" casters

1

I am trying to get a Linorobot ROS based robot to behave correctly. Like the Ubiquity robot I chose to have two rotating cart-style casters (vs. the usual omnidirectional ball casters.)

When I go from going forward to turning in place, or from turning left to turning right, the two casters take a moment before they turn to orient consistent with the direction of turn, and as a result they “steer” the robot in the wrong way. And, as a result the odometry is totally wrong.

Have you at Ubiquity seen the same thing? Did you have to customize the kinematics to accommodate this? Or if not how do you deal with that scenario?

2

This is a known problem with rotating cart-style casters. Obviously rotating cart-style casters have other advantages (e.g. high payload capability, high reliability they don’t gum up with dirt so easily etc.) You’ll note that with Magni we designed the robot to have huge drive wheels and low friction casters so that the drive wheels overwhelm the steering effect of the casters.