In the last post I wrote I would work on some software for the Decawave modules in the last part of the week. But as the team had to split for the week-end, I gave the modules to Perceval and focused on the mechanical design of our robots. It’s hard to admit it but I think I like it, but of course what I do is heavily based on intuition rather than real knowledge.
So I started to design the robots wheels. I created the ball caster (in the left of the image), and after 3 attempts we had a quite convincing solution. For now the ball is made of 3D printed PLA, but it will be replaced by a PTFE one when we receive the order. Using PTFE should lower the friction, but it is quite low already, so we will be able to test our prototype as soon as it’s ready.
I also made a prototype of wheel. I first had to measure the angular velocity at the output of our motoreductor, which is about 6.7Hz under a reasonable load, to guarantee that our robot could reach the 0.7m/s required by our specifications. Then I designed the wheel. I tried to make it flexible to maximise contact area with the ground, hence the spiral and the thin parts. The wheel was printed and then dipped in acetone, this has two main effects :
- improved strength of joints in between layers
- PLA becomes more flexible
Apart from that, I created my first part with ExpeditionPCB (our controller, the STM32F303R6T6). Fortunately, the tougher part (the pad stack, i.e. the footprint of the part in the PCB) was already done, and all I had to do was to adapt the schematic from a similar STM32.
In the next few days I’ll keep on working on the mechanical design, creating the structure and the system holding the balloon above the robot.