Archive: October 2022

Taking advantage of a good discount, four webcams were purchased to reach the total final amount of cameras needed on board. They are all 720p HD cameras with USB connectors, ideal for computer vision tasks since the video stream is light enough for a Rasberry Pi. Full HD cameras (1080p) are also great, but one of the objectives of this project is to make the system as light as possible. Anyway, the four webcams will be added to the already existing three cameras to get a total of seven onboard cameras that will be used for the following purposes: 1x MasterCam (on the Mast), 2x NavCam (Navigation Cameras - on the Mast), 1x HazCam (Hazard Camera - rear of the rover), 2x SurCam (Surrounding Camera - LHS and RHS of the rover).

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

Mimas Rover will have an autonomous navigation capability and to achieve it, multiple systems will be used, one of which is the "Green Lines Algorithm" (GLA). This algorithm is still a work in progress, since June 2022. This post will not go in-depth with this algorithm since it still needs several improvements. In order to do some tests (the rover structure is not ready yet, hence a real driving test is impossible at the moment) a simulation of the Mars surface was made, modelling the terrain in Blender. Then, a webcam was placed in from of the laptop screen and the algorithm was run to test its efficiency. Despite the results are still not great and the GLA requires several improvements, the main principle of the algorithm showed to work correctly: rocks and possible hazards are detected!

• [Hours of attendance: >20h]
• [People involved: Giorgio]

The rocker joint base is one of the parts subjected to continuous stresses while the rover is driving. There is one rocker joint base located at each side of the RB suspension system. These couple of components handle the entire rover's weight, so they must be very stiff and ready to resist stresses. Printing the first piece required 21 hours and 25 minutes, so will be for the second one.

• [Hours of work: 4h]
• [People involved: Giorgio]

Stereo vision is how humans perceive depth. The word "stereo" means “two.” Humans look at the same scene from two different viewpoints to get a sense of depth. So, in order to simulate it, two identical cameras are required: a gaming console stereo camera was bought for this purpose. However, the company that produced the camera made a custom USB 3 cable connector, to let it be usable only on their consoles. To overcome this problem, a common USB 3 cable was cut and tin-soldered to the camera cable, essentially stitching them together. This operation required a series of delicate steps and, in the end, all cables were shielded to avoid electromagnetic interferences while operating. Another challenge was to implement custom open-source firmware to communicate directly with the camera hardware. The final result works quite well and a few depth perception tests were carried out.

• [Hours of work: 4h]
• [People involved: Giorgio, Akshit]

After several days of printing, the first half of the Rocker-Bogie suspension system is ready! The PVC tubes used to connect all printed parts together are not very likely to be used in the final design, since they may be too flexible. At the moment, the plan is to substitute them with aluminium tubes to ensure a higher stiffness as well as a lightweight structure. Nevertheless, the picture below gives an idea of the final shape of one-half of the suspensions, for the first time. A closer look will show that the "C" shaped bracket of the wheel on the left-hand side is missing, so the servo motor mount is simply leaning on the wheel. If everything goes as planned, this assembly should be ready for testing, with bearings, bolts and nuts in the correct place, in three weeks.

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

On Thursday 13th of October 2022, we started updating this logbook. Mimas Rover's journey officially begins now! All posts with dates previous to 13/10/2022 have been written retracing the work done during the months.

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

Especially if driving on rough terrain, Mimas has to turn in order to avoid potential hazards. The rover has two possible steering options: normal steering, also known as Ackermann steering geometry (the four angular wheels turn on the Z-axis to let the rover draw a circle) and turn-on-spot (where the four angular wheels turn on the Z-axis to let the rover rotate on its Z-axis).

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

Even if the wheels were built in July, the suspension brackets needed to make them functional have always been a major point of concern. The "C" shaped brackets are crucial since the entire rover's weight relays on them: they can not make contact with the ground or with the wheels themself. The result obtained at the end of more than 20 hours of printing, is a strong bracket that can easily handle roughly 2kg of weight. This limitation, however, can be reduced by changing the position of the "U" shaped brackets inside the wheels (wheels structure: 03/07/2022).

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

The Rocker-Bogie Suspension System (RB) is mainly based on trigonometry and inverse kinematics principles and needs several mathematic calculations to make it work correctly. When the rover will be fully assembled, several accelerometers will be placed on the suspensions, in order to evaluate their inclination respectively to the ground. As the name suggests, the RB can be subdivided into two parts: the Rocker and the Bogie, each of them must be at an acceptable range of inclination to avoid the rover from toppling over.

• [Hours of work: 5h]
• [People involved: Giorgio, Akshit]

Ten printed components and several weeks after the first version, the mast structure is finally ready! It is not fully assembled, though: some tiny brackets and holders for the cameras and sensors still need to be printed, and the electronics themselves is not wired yet. The empty space at the bottom of the mast will host a Nema 17 stepper motor to allow a pan rotation of the Imager, thanks to a threaded rod.

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