Hi folks, and thanks for looking in!

This thread is a retrospective build diary for the robot we took to the Robodojo Sportsman competition on the 27th. This was our first time building a robot and was quite a learning experience. I intended to start a build diary here pretty much every day for the last month, but every day I was too busy building or designing the robot, trying to find/order the right bits on RS, or sulking because something had gone wrong. Hence this will (mostly) be a look back at what I did at the time, probably more for our benefit than for anyone else's interest.

First, a brief introduction… we are team Designed for Demise, consisting of me, Becky (RainbowCello) and Simon (stl100). All long-time Robot Wars fans, first time builders. If anyone’s interested in the team name by the way, it’s derived from a design approach to ensure that broken satellites don’t hit people or other satellites (see here). When I first heard the term I thought it sounded like a great name for a metal band, hence the gothy font on our team T-shirts.

I always fancied having a go at combat robotics (like, since the first episode of RW in 199, and when I left my job a year or so back, my colleagues (knowing this) very generously gave me a DX6e as a leaving present. Since then I have bought a few bits and wired up some gubbins in a Lego chassis, but found it hard to start building a proper ‘bot. Here's a Lego sort-of-beetleweight (no ESCs or battery at the moment):
DSC_0570.jpg

The Robodojo Sportsman competition offered a slightly lower entry bar, and so when the second FW event was posted up at the end of last year we rather impulsively signed up, on the basis of a discussion lasting about 30 seconds:

  • Me: Can we build some kind of crappy robot in a month? For that Sportsman thingummy.
  • Her: Errrrr... yeah probably
  • Me: OK I’ll sign us up then. Shall I say definite? It says priority for definite attendees. I’d better say definite.


Ten of your Earth pounds later and we were IRREVOCABLY COMMITTED to definitely build said crappy robot, with absolutely no way of backing out. Of course, we didn't have a month to build the robot, because we had visitors the first week of January and then I was away for work until the 9th. Still, that left nearly 20 days. Of which I would be away for 9 days. So actually, 11 days.

So, on to the robot itself… To give us something to start with, we set ourselves a few design constraints (in addition to the FRA/Robodojo rules):

  • Use 2x Argos drill motors for drive with a FeatherTwo ESC
  • Weapon should be a simple "grabber" arm run off a gearmotor, as that seemed like the easiest thing to bodge together quickly
  • Basic design has to be able to run as just a wedge in case we don't have time to finish the weapon (likelihood: high)
  • Make from mostly HDPE as it's easy to work with (admittedly this was a theoretical assumption, I'd never tried before)


PREP - up to 9th Jan
I ordered a cheap gearmotor from eBay in the first week of Jan, as that was the only "long lead" item we had to worry about (though in the end it arrived from China in a few days). I selected 30 RPM by sort of moving my arm around in a 180° arc in what felt like about a second and trying to imagine that my arm was the weapon on a hypothetical robot. On reflection, I do not recommend this technique for component selection.

We also spent a bit of time discombobulating Argos drills; the first one went a bit wrong, as I didn’t really read the motor removal instructions and just attacked it, eventually ending up with this:
DSC_0569.jpg
I may have lost my temper with this one. If anyone has any idea how to get that last bit of chuck off, I’m all ears.

Finally, I ordered a relay switch and some HDPE from Direct Plastics.

10-11th JANUARY (Design)
Having absolutely zero points of reference for how to start designing a robot, I had to spend some time vaguely figuring out the layout for the thing in my head. I've been trying to figure out Fusion 360 for the last year so I fired it up and started sketching. My current level of expertise with F360 consists of frowning at the computer and wondering why it has to be different from SolidWorks.
The two drive motors and the weapon gear motor were the only known quantities, so most of the chassis was designed around fitting them in. I then added a box on the back that could accommodate something around the size of a 4s 3000 mAh LiPo plus some extra space for other electr(on)ic gubbins.
The fruits of my initial CAD work, after a couple of days' work:
CAD1.pngCAD2.png

Mostly made of HDPE, wheels at this point completely unknown provenance (other than "about 120 mm diameter"). The front prong/wedge and sides of the overhead grabby arm were meant to be made from some steel bar bought from eBay, with teeth made from M6 stud. The mount for the gearmotor is designed to be cut from a piece of scrap ally that I saved from the bin at work.

Up next: actual building, which I suppose is what this forum is meant to be about