Building a Robotic Rock Crawler ChassisFollow article
This article aims to explore the use of DesignSpark Mechanical in the design and build of an all-terrain robotics platform. The design was inspired by the intrepid rock crawling and overlanding vehicles that are used to navigate the most extreme driving landscapes seen around the world.
The principal requirement for this design is the capability to help develop and test the practical applications of emerging technologies in the interest of pursuing environmental conservation and sustainability projects. This will include a portfolio of computer vision and machine learning, advanced environmental sensing and the latest IoT standards with a specific focus on Bluetooth 5.
The following sections will detail the thought process behind the design, a bill of materials, a quick look at the different sub-assembly models and a review of the results.
The intrepid rock-crawler in action.
Bill of Materials
- Black and orange PLA
- Aluminium profile
- Igus ball joints
- DC gear motors
- Silver steel rods
- Coilover springs
- 8mm shaft coupling
- High-profile pneumatic tires
Design and Modelling
Work on this project started around a year ago with a strong focus on lessons learned from the previous platform leading the early design stages. The most significant requirements for the new system were greater flexibility in the vehicle’s terrain response and shock handling capabilities which could both be addressed with the addition of an off-road style suspension system. There were a great many resources and references online which included documented diagrams, YouTube videos and coverage of the Dakar rally shakedowns which helped in deriving a viable design.
Exploded view of the axle.
Conventional off-road suspension systems consist of two solid-axles connected to a sturdy ladder-frame chassis that both aid in withstanding the mechanical stresses of off-road driving. The axles, in this case, were designed around a pair of inline DC gear motors that improve on conventional four-wheel-drive designs by driving each wheel independently and giving each axle a higher degree of torque control than its petrol-powered equivalents. The automation of each wheel simplifies the design by replacing any conventional steering components with electronic differential steering that can change the direction of the platform using relative wheels speeds across the axle.
Suspension linkages, coilover springs and axles.
The requirements for the suspension system emphasised a need to maintain tire contact with the ground at all times in order to maximise traction over loose and rocky surfaces. A four-link system was chosen to mimic the high levels of axle articulation observed in extreme off-road vehicles such as overlanders and the go-anywhere rock-crawler. The four-link suspension system notably contrasts from traditional solid-axle designs through the use of four connecting rods that govern the rotational freedom of each axle while maintaining their alignment with the chassis. This unique articulation helps optimise grip by distributing weight evenly across each wheel despite any uneven surfaces.
The four-link system in this project was designed around a series of ball joints and custom threaded rods that were used to connect the axles to the ladder-frame while using adjustable coilover springs and dampers to control the articulation of each wheel proportionally to any changes in the terrain.
The assembled ladder-frame chassis.
The ladder-frame chassis was the most important structural component considered for the platform as it supported both axles through their respective suspension mounts and linkages. It is important for the chassis to maintain structural rigidity in the interest of handling and predictability over tough terrain. The ladder structure, in this case, was designed around two aluminium struts that provide convenient mounting points for both the suspension components and an array of interchangeable electronic sensing and control modules. The cross members of the frame were modelled within DesignSpark Mechanical, exported, sliced and 3D printed to create a remarkably strong structure.
Wheels coupled to motors.
The assembled chassis is supported by four high-profile pneumatic wheels that were carefully selected based on their ability to maintain traction and reduce shock during adverse operating conditions. The malleable nature of each tire also helps reduce vibration when performing tight turning manoeuvres as part of the differential steering and dynamic terrain-response systems.
The original roller bearing assembly of each wheel was replaced with a custom five-spoke rim that was modelled and printed around a metal flange coupling. The modified wheel assemblies could then be reliably secured to the flatted profile of each motor shaft using a grub screw that could withstand the high torque values applied to each wheel.
Results and Conclusions
Comparing the finished build with the CAD model.
The success of this project was largely contingent on the rapid-prototyping capabilities offered by DesignSpark Mechanical in the production of bespoke 3D printed components. These components were modelled and exported in a high-resolution format which helped reduce the risk of any visual discrepancies and mechanical tolerances while increasing the quality and strength of the print.
The combination of 3D printed and COTS components was used to create a strong yet configurable chassis structure that could be adapted to fit many different applications. The aluminium struts used in the ladder-frame provide versatility to the suspension components while protecting any electronic equipment mounted to the top of the platform.
The adaptable nature of the ladder-frame will also facilitate a range of interchangeable electronic modules in future iterations of the project, with different sensing, telemetry and control loadouts being made available for mission-specific applications. These modules will be key to developing the robotic capabilities of the platform as a testbed for a range of technologies and evolving IP.