Otis Dynamics Robot Arm

The first system CAD is an early proof of concept. That arm used cycloidal-drive gearboxes, servo-actuated fingers and hands, and was driven mainly by NEMA 17 and NEMA 23 stepper motors. It was a personal project to prove the idea before the current generation.

The assembly now lives in Onshape. The arm is designed so it is easy to assemble and manufacture: tools can reach the fasteners, and bolts and spacers are not buried. Brass heat-set inserts in the printed parts have been useful many times. A clearance hole plus a bolt into the insert makes a joint that is hard to pull apart by hand. Those connections keep the longer linkages attached to the motor mounts so the adapters do not fall off the arm.

The current arm is printed and assembled. It matches the Onshape model.

Codex helped me build Otis Motor Studio, a tool that sets position and jogs motors over CAN. The first setup was a USB-CAN adapter on a Windows 11 laptop, DC power to each motor, and CANH and CANL on the motor leads. That worked with the RS00, RS02, RS03, and RS04. Motor Studio went through many iterations until it ran consistently. It supports angular velocity and acceleration control, and it plots torque.

Otis Motor Studio Multi controls several motors at once over USB-CAN. That was required to test the wiring as the motors were connected together.

Motors were validated in a fixture I built for torque testing. The RS02 is rated for 6 Nm continuous. The motor was mounted with a lever arm that pressed on a food scale, and the manufacturer claims held up. A continuous test lifting and lowering a 5 lb weight many times showed how hot the motor got. It stayed efficient, and temperature did not look like a problem. Fans will still go in and around the arm so the motors do not overheat and lose torque.

After the CAD assembly was done, the parts order included screws, butt connectors, ring terminals, a lot of XT30 connectors, mixed-gauge wire, and the rest of the hardware.

After the arm was assembled, I opened the Onshape URDF in ROS 2 Jazzy. For a first look I used the viewer at viewer.robotsfan.com. It loads the arm in a browser so I can move the joints and check collisions, which is much faster than standing up ROS 2 for that first check.

I run the arm in Gazebo Sim, the physics simulator. The screenshot is the arm on a table in that world.

RViz is the ROS 2 visualizer. It does not run physics. It draws the model from /robot_description, and the pose matches Gazebo because both follow the same /joint_states.

Otis Arm Console is a local web app I built to drive the six revolute joints for presentations. It has sliders, jog buttons, and named poses such as simulation_zero, with positions in degrees. The page is labeled simulation control only.

The screencast is that console next to Gazebo while I jog joints, then RViz and Gazebo side by side on the same pose. When a slider moves, the console shows joint target accepted, and the Actual angle lags the Target while the controller runs the trajectory.

rqt_graph in Nodes/Topics (active) is the running graph for this sim. Ovals are nodes. Rectangles are topics. Arrows go from a publisher to a topic, then to its subscribers.

/gz_ros_control, /simulation_clock_bridge, /arm_collision_guard, and the TF listener sit on the graph with no topic edges in this snapshot. rqt_graph hides some topics depending on filters. The console still reports Collision guard: ready. gz_ros2_control is the Gazebo plugin that instantiates a ros2_control controller manager and connects it to a Gazebo model.