Progress seemed to be moving very fast. But as with any project, I soon hit a rather large and scary brick wall! When powering the Pi on, I suddenly got a rather large ploom of smoke and a strong smell of burning plastic. I quickly sprung into action, tearing the circuit apart to try and stop it developing, which thankfully was successful. Having a cardboard chassis isn’t the most fire retardant material, so i can only imaging what would have happened. Once everything had cooled down, I assessed the damage to see that all the hardware was ruined.
- The jumper wires seemed to have melted
- The connectors on the ThunderBorg had also melted
- The Pi was no longer powering on
I posted onto the PiBorg forum, which they also confirmed everything was to be deemed unsafe to use. To reduce further delay, i bit the bullet and purchased 2 new motor controllers and a Pi 3B+
Whilst this hardware was on the way, I decided to evaluate my prototype, and look at what went wrong, as well as what could have possibly gone wrong. From this, I deduced the following:
- All the hardware needed properly mounting, moving hardware could short, causing another fire
- The battery needed added protection, having it balancing on the other hardware was a disaster waiting to happen
- The Pi needed to be covered or properly mounted to reduce risk of static damage
It came at the best time, that I had actually arranged 3 days off to work on progress, however I didn’t have a bot to work on. The new hardware wasn’t due to arrive until at least day 2, so I decided to focus this time on fixing the above issues. I am lucky enough to have a 3D Printer in my arsenal, so I loaded up my SketchUp and set about fixing the problems.
1 & 3 – Mounting Hardware & the Pi
First of all, I wanted to solve the mounting issues. To do this, i decided to start off by adding a new layer to my cardboard contraction of a chassis. I added 40mm standoffs, and bolted a second layer to the existing chassis. This made a nice new and spacious platform to add more components. I wanted to add a User Interface to the robot , to avoid me having to walk around with a laptop on the day, so I decided the Pi was the best thing to add to this layer, as it will be where the screen is mounted in the future. The next problem I wanted to solve, was how to protect the Pi, to reduce the risk of static damage and components being shorted. To do this, I created a stand angled at 45° to create a steady incline, which will be ideal when i add a menu in the future.
I used all the official Pi dimensions to get the correct dimensions for the stand-offs, so luckily everything printed correct first time. My printer (an XYZ Davinci Jr) Struggled a little bit with the overhangs, however it was fine for an initial test. After mounting it all up, it seemed to do the trick. It enabled the pi to be angled at thee correct angle for the Pi, as well as enabling i to be effectively secured to the chassis.
2 – Battery protection
The next key aspect of the robot robot I wanted to focus on was battery protection. To do this, I wanted to design a tightly fitting shroud, that could protect the battery, but also enable it to easily be swapped out, as well as all the cables being easily accessible. Again, I got my head down in SketchUp, and came up with the below holder. The battery is very tightly fitted into the shroud, with a sliding hatch to secure it in place, but still allow the cables to be accessed easily. In future revisions, I hope to be able to alter it to hold the voltage indicator.
By this time, the new parts had arrived, so I swiftly re-assemble the chassis with improvements and tested.
— Alex Smith (@ajalexsmith) October 30, 2018