Category: Mimas Rover

After partially disassembling the rover for the journey from Bainfield to Merchiston, it was decided to test all the components to ensure no parts have been damaged during the transfer. This was also a great occasion to test the computer vision algorithm for the first time, in an open-space environment: the lab is large enough to allow drive tests, which will be conducted in the following weeks. At the current state of things, the motors are still not wired and the only fully functional component is the Mast Tower. The "Green Lines algorithm" has been tested using a cardboard box as a rock. For the test, Mimas was placed on custom-made metal perches that keep the rover at the right height even without wheels.

• [Hours of work: 2]
• [People involved: Giorgio, Akshit]

On the 8th of February 2023, Mimas was moved from Bainfield Student Accommodation to Merchiston Campus, room D66. Thanks to Brian Davison, Alexandros Gkanatsios and Stuart Thomas, we got access to a brand-new laboratory to work on the rover! The lab has a workstation for soldering, whiteboard tables for sketching (and, most importantly, a lot of convenient electric plugs!). It took several hours to pack Mimas, ensuring she is safe during the journey from Bainfield to Merchiston, and when the rover arrived at its destination, the help from the ENU Formula Student team was invaluable. Mimas will stay in D66 for 8 weeks and during this relatively short period of time, it will undergo several changes, wiring, and drive testing. As the Honours Project report submission day gets closer and closer, the construction of the rover becomes more challenging.

• [Hours of work: 6]
• [People involved: Giorgio, Akshit, w/ENU Formula Student team]

The "rocker" joints were always one of the major issues with the Rocker Bogie designed for Mimas: since the entire weight of the rover relies on them, these particular pieces have to be extremely solid. The first design suffers from excessive stress, especially in the area of connection between the joint and the rover body. A deformation of <1mm was measured: this was not a big threat, however, the design has been revisited. The new rocker joint has a thicker structure in all directions, and the connection between the joint and the rover body is reinforced by a custom M8 metal flange. This helps better distribute the load on the joint. In addition, four threaded inserts have been added to make the rocker joint tube attachment stiffer.

• [Hours of work: 5]
• [People involved: Giorgio]

After several upgrades to the suspension system, after installing the plastic plates that were realised by Brian Black and Paul Murray (technician at Merchiston Campus's workshop), Mimas was finally ready for another standing test! The Rocker-Bogie (RB) successfully held the rover in position, guaranteeing sufficiently strong support for the heavy rover body. The elasticity of the in-wheels suspensions ensures a springy reaction to bumps and terrain irregularities. The RB, however, still needs upgrades since the hollow PVC tubes are severely stressed by the rover's weight. This topic will be covered in a future post.

• [Hours of work: 1]
• [People involved: Giorgio]

Samples catching is a crucial aspect of this project: Mimas itself is made to carry a set of sensors and devices to collect information from the surrounding area. Collecting small samples of the terrain is a great way to study a planet's geological history and look for signs of life. After all, these are the objectives of the rovers sent to Mars! For this project, hermetically sealed sample tubes are not an option, since they would require a level of designing and machining far more complex than what we can do in such a short period of time. For this reason, the sample tubes made for Mimas are PVC tubes with a custom 3D-printed base that will be held in position by the sample tubes carousel. This mechanism is inspired by the drill bit carousel used for Perseverance, but instead of delivering the correct drill bit for the robotic arm, it rotates, exposing the first empty sample tube ready for filling.

• [Hours of work: 1h]
• [People involved: Giorgio]

The six wheels have a design inspired by Perseverance wheels: before discussing the choices made for Mimas, it is worthy to briefly analyse the design made by JPL for their rovers. Machined out of a block of flight-grade aluminium and equipped with titanium spokes, each one of the Perseverance's six wheels is slightly larger in diameter and narrower than Curiosity's, with skins that are almost a millimetre thicker. They also feature new treads or grousers: In place of Curiosity's 24 chevron-pattern treads are 48 gently curved ones. For Mimas, steel was used to make a strong and flexible structure with inner suspensions made of bendy but strong steel strips. To obtain the 48 treads, the plan is to use a strong rubber (PU PX60) that will act as a tyre. In reality, rubber and plastic materials are not allowed for travels to Mars, since at very low temperatures, rubber acts as glass, becoming very brittle. Thanks to Lynn Chalmers, the technician for the polymers laboratory at Merchiston Campus, the manufacturing of the six wheels for Mimas can proceed smoothly!

• [Hours of work: 3h]
• [People involved: Giorgio, Lynn]

Even though a Mars rover's aesthetics aren't precisely a top concern, success also depends on how the vehicle is painted. White paint may provide a vital reflecting surface for any space-bound item in addition to giving it a simple, clean appearance. And, as John Campanella (the lead painter of Perseverance) said: "any good paint job is preceded by a great tape job". Mars 2020 employed primer and paint that were far from typical of a hardware shop. They have undergone extensive testing to show that they can adhere to aluminium, withstand shocks, vibrations, UV rays, and other annoyances of a trip to Mars, as well as be tough enough to survive the Martian cold, all while not outgassing organic compounds and other materials that could affect the mission's science experiments. On Mimas, the painting used is an enamel paint, a type of paint that air-dries to a hard, giving a glossy finish. It is ideal for coating surfaces that are outdoors or otherwise subject to hard wear or variations in temperature: these characteristics look ideal for the purpose of the project. The photo shown below is the first layer of painting made on the Mast Tower.

• [Hours of work: 6h]
• [People involved: Giorgio]

All sensors, motors and other electrical components located outside the Rover's belly, will be connected to the Raspberry Pi4 through cluster cable connectors attached to the WEB. The 3D component shown below can host up to 12 cables: 6 for the wheels on each side of the rover (each DC motor has 2 wires), and 6 for the servo motors located on top of the steering wheels (each servo motor has 3 wires).

• [Hours of work: 1h]
• [People involved: Giorgio]

The Emulated "Mars Environmental Dynamics Analyzer" also known as E-MEDA makes weather measurements including pressure, temperature and humidity, emulating the sensors used on Perseverance. The temperature sensors are housed in two small Booms structures mounted orthogonal to the Mast Tower of the Rover. For Mimas, two types of sensors were selected: the component shown in the picture above is attached to the Mast through an M3 bolt inserted in the 3D-printed part by melting the plastic. A precise description of the E-MEDA system will be provided in a future update.

• [Hours of work: 2h]
• [People involved: Giorgio]

On the same day of the first "standing" of Mimas, Merchiston workshop technicians helped us make custom bolts for the Rocker-Bogie: each bolt (threaded rod, more precisely) passes through the suspension tubes and is secured at both ends with washers and nuts. Also, the "bogie" part of the suspension system was moved closer to the "rocker", removing an M8 nut, and replacing it with a big washer.

• [Hours of work: 1h]
• [People involved: Giorgio]