The Cablecam Can Get Incredible Shots with a Minimal Number of Components
By hoisting a camera on a motorized rope and pulley system, the Cablecam is able to shoot amazing footage while remaining smooth.
The purpose
Filmmakers and videographers are always on the hunt for that perfect angle or motion that causes their work to look great on screen. Certain motorized systems allow these artists to easily achieve this goal by smoothly sliding the camera along either a rail or with a set of wheels on the ground. However, they can quickly become quite expensive and therefore out of reach for many independent creators, which is partially what inspired Maximiliano Palay to create his very first attempt at a moving robot: the Cablecam.
Components used
The Cablecam project is, in essence, a single motor that when spun causes its attached assembly to get propelled along a rope. The rate at which this occurs and its position are controlled by a ground station with a Jetson Nano at its heart. Palay went with the Nano because he wanted to make use of its powerful machine learning capabilities. The Raspberry Pi 4 on the Cablecam sends a constant stream via UDP to the Jetson Nano, which in turn draws bounding boxes around objects or people of interest and sends commands back to the Pi.
Once a command has been received by the Raspberry Pi 4, it outputs signals to the brushless electronic speed control (ESC) module that drives the motor. By doing it this way, the user can view what the Cablecam is seeing in real-time and has the ability to finely tune the rate of acceleration and speed.
Designing the device
Palay designed the camera mover in Fusion 360 with the intention of being able to easily 3D print the pulleys/gears and laser cut the outer framework.
As seen in this brief video, the gearing for the brushless motor and drive system reduces the output of the motor by a factor of 5.4:1, as that value was found to be the optimal mix of acceleration and speed.
Fabrication
After he was finished designing the model, Palay began the fabrication process by cutting out four panels from a single sheet of wood with the help of a CNC mill. Next, he printed out four gears for the drive mechanism and a pair of pulleys to guide the rope. They were attached to the frame with a set of threaded rods that allowed each one to spin freely.
Because the ESC had no reverse capability, Palay had to solder the two motor wires onto a relay module that reversed the polarity whenever the direction was supposed to change. The camera selected for the Cablecam was a basic Arducam that was placed into a 3D-printed enclosure and mounted onto a Tarot Gimball. In the future, this camera could be swapped out for a GoPro if better picture quality is needed. And finally, several recycled laptop battery cells were joined together in order to provide power to everything.
Operating the Cablecam
The Cablecam can run in one of two operating modes: manual or auto. At first, Palay tested out the manual mode by using the base station's potentiometer to adjust the speed and direction of the camera system. Next, the autonomous mode was selected, and as seen in this demonstration video, a bounding box can be clearly seen around the subject as he walks to the left. Likewise, the Cablecam begins to move that direction too in order to keep the subject in frame.