Hi!
I’m currently undertaking the task of building an indoors-outdoors urban robot and have come across a chassis that has an ackermann architecture but there’s no direct actuation in the steering mechanism, instead it has 4 actuated wheels and the steering angle is controlled by the speed differential of the two front wheels. If the robot were turned off you would be able to manually change the steering angle of the two front wheels without finding any resistance, because there’s no motor there, only a pivot.
An example of this chassis is segway’s RMP 401, which seems to have had some adoption in the industry by companies like Coco and Goggo network.
This chassis seems to have some advantages with respect to 4 and 6 wheeled differential chassis, particularly they seem to provide very smooth and agile motion with minimal vibration when operating within the ackermann kinematic constraints (video), while still allowing for almost zero turn radius operating like a 4 wheeled differential (video).
I’m curious to hear if anyone in the community has experience with this kind of hybrid ackermann-differential chassis, particularly regarding:
- The controllability of the steering mechanism, does your chassis have any kind of feedback on the steering angle despite not being actuated? How controllable is this angle?
- How much stress is put on the wheels/motors when making near zero radius turns? from the video it seems like there’s quite a bit of wheel slip when operating “outside” what the ackermann kinematics would allow to move as.
- Maneuverability: How hard is for the chassis to go through tight spaces, such as doors? how would it do for example going in and out of an elevator? How would it do parking/docking?
- Integrability to ROS ecosystem: I don’t think there’s support either for ros2_control or nav2
Thanks in advance for any opinions you can provide!