Arips always had problems with overcoming small steps and bumps as they occur on door edges if the floor of different rooms isn’t exactly the same height. Especially the passive caster wheel would often get stuck on the edge. I tried different caster wheel sides and rubber types for the main wheels, but no approach was satisfactory. It even happened that the robot completely tipped over the rear caster wheel while doing rapid back and forth movement. Since I want it to be mechanically safe no matter what the software does with the motors, I decided to put the robot on tracks instead. Ideally they would provide a stable contact area without the danger of falling over in any direction. Unfortunately this didn’t go to well either, so eventually I ended up mounting the previous differential drive and slightly improving the caster wheel again.

Finally, I got a working proof of concept of autonomous door opening. This is the first step to enable ARIPS navigate in my appartement even if a room door is closed.

Using its arm, ARIPS can grasp and move around small objects. Here is a simple demonstration, where a detected object is picked and dropped back onto the floor. In the top left corner the rviz view from the onboard Kinect’s perspective of the scene is shown. The detected object is marked as a green cube. Note how the calibration plate is fully visible to properly compute the Kinect’s current pose.

The Kinect RGBD sensor on ARIPS is mounted on a moveble joint can can be tilted up and down with a SCS215 servo. Due to inaccuracies of several mechanical parts, the exact tilt angle of the Kinect can be perceived only up to a certain precision. Also the xyz position offset is not completely fixed, since the mounting rods can start to oscillate during acceleration and breaking of the robot when driving around.

ARIPS Arm v2 is built with Feetech SCS215 servos which are a cheap but powerful alternative to the Dynamixel AX-12A. Just like the Dynamixel servos, the SCS215 provide positional and torque feedback over a serial bus interface. The positional resolution is 10 bit, i.e. 1024 steps. With a rotational range of about 300 degrees, this means about 0.3 deg per raw step. However, the internal potentiometer seems not to provide fully linear feedback w.r.t. the rotation angle, and also each individual servo has a slightly different angular offset.

The ARIPS Arm is a custom designed 3D-printed 5 DOF robot arm with a gripper at the end effector. It is built mainly with Feetech SCS215 servos, which are quite precise and have a positional feedback.

This is ARIPS, a mobile robot platform equipped with a 2-wheel differential drive, a kinect, a LIDAR, and a custom 3D printed robot arm.