Chassis Design - An Ode to Inkscape

So, we've got all these lovely goodies to build into our final, competition-ready Spot:Bot platform but we need to find space for it all and plan wire routing so it's not just a mess of unfathomable spaghetti. Yes, we could build this onto a bucket and just throw everything inside. It would do a good job of ferrying all our parts around but that won't be much fun to troubleshoot when things don't work as planned.

We're big fans of Inkscape in this team, a very versatile vector graphics drawing package. One of our team members uses it all the time for work and play. Everything from Org diagrams to systems network designs to helping kids turn their drawings animated game sprites in their Scratch games. It's great as a white-baording tool for planning optimal layouts to meet physical space constraints too. It's free to download and available on many platforms.

Anyway... the last thing we want is to start drilling holes all over our lovingly jigsawwed boards of ply (our chassis layers) to mount various things on to it only to find out that we very quickly run out of mounting options for later components to be added to the mix. Planning and design are key to efficiently fitting the maximum amount of robot bling into the minimum amount of space.

We started by listed all the components that we needed to fit into Spot:Bot. These are as follows:

  • Raspberry Pi 3B
  • PiBorg Thunderborg
  • Motor Battery Pack
  • Pimoroni Pan/Tilt HAT
  • Pimoroni Breakout Garden OLED
  • Pimoroni Breakout Garden ToF Proximity Sensors (x3)
  • Pimoroni Breakout Garden 6DoF Motion Sensor
  • PiBorg ThunderBorg Motors (x4)
  • PiBorg Motor Brackets (x4)
  • Wheels (of course!)
  • Adafruit I2C Multiplexer
  • Wiring looms

We took measurements, created a scale diagram of all the parts with Inkscape and started to move parts around the screen as we discussed the best layout and what should go where. We could have done this with bits of paper on a table but committing it to 1's and 0's on a computer allows us to revisit and refine the design as we learn more (and remember parts we need to find space for that we had previously forgotten about).

Here's our very first version of a top down Spot:Bot chassis design. It's not truly CAD precision but it's good enough to prove to ourselves that we can fit everything on board. It's two layers, with the upper layer housing motor controller & pan-tilt HAT and also providing a secure housing for our motor battery pack.

NOTES:

  1. The ToF & 6DoF sensors will be housed in casings being designed and laser cut for us by Dundee Makespace, courtesy of our associate team mate, Kerry Kidd. We don't actually know their dimensions yet so we've used upper bound estimates of what size we believe they will be for now.

  2. You may have spotted thatv the diagram shows 5x ToF sensors whereas our parts list only shows 3. In reality, the side sensors will either be mounted in the centre of Spot:Bot or at the back, but not both. We may choose to swap locations from challenge to challenge depending on which location works best. However, we needed to be able to plan for enough space in both locations to avail oursleves of this option.

UPDATE (MARCH 2019): Having started to build our final competition-ready platform, here's an eaxample of what the above chassis layers actually looks like in the flesh, before most of the sensors etc... have been added:

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