Stereo depth on a small robot usually means one of two things: a closed commercial depth camera with its own SDK, or a single-board computer with two USB webcams taped to a bracket. A new open-source project called 4reel, from the developer who publishes as machinehum, aims at the space in between. It is a compact camera board built on the Rockchip RV1103 with two OV9281 global-shutter image sensors. It can run standalone Linux or act as a vision coprocessor that reports to a microcontroller over a serial link.
Hackaday covered the board on 21 October 2026. The creator's own write-up on the Rootkit Labs blog is dated 6 October 2026, and the design files are on GitHub under the MIT license.
The Silicon: A Small Camera SoC, Not a General-Purpose SBC
The creator's write-up gives the RV1103 as a single-core 1.1 GHz ARM Cortex-A7 with 64 MB of DDR2 and a MIPI CSI-2 camera interface, in a QFN-88 package. Hackaday reports the same core figures (1.1 GHz single-core ARM, 64 MB DDR2, MIPI CSI-2) and adds that the board carries 4 MB of flash and 10/100 Mbit Ethernet.
Those numbers matter. The RV1103 is a camera-oriented part, and 64 MB of RAM is tight for a Linux system that buffers two image streams. Anyone hoping to run a full desktop vision stack on the device should look at what the repository actually ships before planning around it. The 4 MB flash figure from Hackaday likewise points to a lean image, not a general-purpose distribution.
The two sensors are OV9281 global-shutter cameras, according to Hackaday. Global shutter is the important detail for mobile robotics. Every pixel is exposed at the same moment, so a moving platform does not get the skew and wobble that rolling-shutter sensors produce. That makes stereo matching and visual odometry much more tractable on a robot that is driving, turning or vibrating.
Hackaday also lists a three-axis accelerometer on the board. Its article gives the part as "LI2HH12". We could not confirm that part number against the repository, so we are not reporting a specific accelerometer model here.
Board Design and Software Stack
The write-up describes a four-layer PCB. The software is built with Buildroot on the vendor BSP kernel. The creator explains that Rockchip's MIPI drivers and hardware accelerators are not in the upstream kernel, so the vendor tree is needed for now. Boot follows the usual Rockchip sequence: BootROM, TPL, SPL, U-Boot, then Linux.
The creator's write-up says image data reaches user space through Video4Linux2, the standard Linux capture API, which exposes the cameras as /dev/videoX nodes. That means V4L2 tooling should be familiar to anyone who has worked with Linux cameras, even though the kernel underneath is a vendor fork. Hackaday likewise points to Video4Linux2 in the software stack.
The GitHub repository describes 4reel as a "Stereo machine vision camera for outdoor mobile robotics" and says it is capable of stereo depth processing, image classification and SLAM. At the time of writing it had 37 commits. The repo has two hardware directories: rv1103, described as the current tested board, and rv1106, described as the next generation. The repository does not give specifications for the RV1106 version, and we are not speculating on them.
Two Ways to Use It
The creator describes two operating modes: serial output to a host, or standalone Linux.
As a networked Linux device. According to the repository, the USB-C port presents itself to a host computer as an Ethernet adapter with DHCP. Plugging it into a laptop gives you a network link with no separate Ethernet cable or Wi-Fi setup. The creator's post says he eventually moved to SSH over the USB-C port acting as an Ethernet adapter. The repo also lists a web portal at http://192.168.77.1:8080/ on that USB link, used for configuration.
As a vision coprocessor. The repository says a JST connector carries UART to an Arduino or ESP32 host and can also power the device from 5 V. This is the more interesting mode for small robots. A microcontroller running motor control and sensor fusion can delegate image work to the 4reel and read back results over a simple serial line. It never has to handle raw frames.
Honest About the First Spin
One unusual thing about the Rootkit Labs post is how openly it lists what went wrong on the first board revision. The creator says he got the board mostly correct on the first attempt, with a few issues:
- The wrong SoC was ordered.
- The lens-mount holes were drilled at 1.8 mm instead of 2.2 mm.
- The 1 k LED resistors were, in his words, "too small to make the LEDs light up nicely".
- The 0.9 V trace was too thin, although the post says it seemed to work fine.
None of these is exotic, and that is why the list is useful. Anyone doing their first SoC board with a dedicated low-voltage core rail will recognise the 0.9 V trace problem. The mismatched mount holes are a reminder that mechanical footprints deserve the same scrutiny as electrical ones. The post also states that it was written entirely by a human, which is worth noting in a period when much project documentation is not.
What It Means for Makers
Who it is for. The repository names outdoor mobile robotics as the target, and the creator's post mentions integrating the board into robotics projects, such as an Arduino needing obstacle avoidance or navigation. In practice the board suits builders who already have a microcontroller-based robot and want depth or classification without moving the whole platform onto a Linux SBC. The UART-over-JST link to Arduino or ESP32, with 5 V power on the same connector, is aimed directly at that kind of user. Embedded Linux developers who want a small, open reference design for an RV1103 MIPI camera system will also find the Buildroot setup and boot-chain notes useful, especially the explanation of why the vendor BSP is still needed.
What it replaces or enables. For hobby robots, 4reel sits between a pair of USB webcams on an SBC and a closed commercial depth camera. Its distinguishing features are the two global-shutter OV9281 sensors, a fully open design under the MIT license, and USB-C Ethernet that makes bring-up and debugging fairly painless. The trade-off is compute. A single 1.1 GHz Cortex-A7 with 64 MB of DDR2 is modest, and the sources do not publish frame rates, depth resolution or SLAM benchmarks. The creator's post lists SLAM and YOLO as things planned for a next stage of the project, so treat those workloads as goals, not measured results.
Price and availability. None of the sources gives a price or a retail listing. The creator's post says he would like to sell a few of the devices and asks interested readers to sign up for email notification; if there are more than 20 signups, he says he will order another 10 boards with all the fixes and list them for sale. He stresses that this is not a pre-order. As of 21 October 2026, 4reel is an open-source hardware design published on GitHub. The rv1103 board is described as the current tested revision, and an rv1106 next-generation design is in the same repository. Anyone who wants one now should plan to build it from the published files.
