Mechanical Cat

Mechanical Cat – the Pembrokeshire Robot Builders Club – is hosted by FabLab. Our downloads have now moved here.


9th July 2018: After many hiccups we finally have part-built circuit-boards on order for our Arduino-based control system. This means they’ll be available for you to buy and build. All the tricky receiver SMDs will be ready-mounted, so you’ll just need to build the transmitter, add a nRF24L01+ module, and wire into your robot. Full instructions are in this download.

Your Maker-Space Can Build Its Own AntWeight Robots And Arena, Too.

Pembrokeshire Robot Builders Club is currently designing this complete AntWeight starter-set. It will include half-a-dozen “play-all-day” robots, an arena, and a proportional radio-control system which can be built from scratch using about £30 worth of components per robot – that’s including the transmitter.

OpenDozer: Four 25mm silicone-tyred wheels driven by 600rpm Pololu motors give this robot the edge when push comes to shove. Quick-change 300mAh battery. Receiver re-programmable in-situ. Runs equally well inverted. 138g. 100x98x25mm.

We’ll be offering this entire project – the arena, the robots, and the RC system – for anyone to download free and open-source.

If you have access to a 3D printer and a soldering-iron then your club or maker-space will be able to build the complete AntWeight arena set without the months-long development process we’ve been through.

What’s It For?

Here at Mechanical Cat we’re going to take one of these AntWeight arena kits on tour around Pembrokeshire’s schools and libraries to publicise the FabLab and our Robot Builders Club. We’ll also package up the robots as robot-building kits for our new members so they will be able to get stuck into building themselves a fun AntWeight robot on their first day in the club.

We think that other clubs and maker-spaces around the UK might like to use our AntWeight arena set to do the same. That’s why we’re sharing the whole thing.

So, on this page, you will be able to download all the software, PCB designs, robot STLs, and arena CNC plans so you can build your own. Or at least, you will be able to as soon as we’ve finished it. It will be a few weeks before we’ve got everything complete, so please check back here to see developments. If you’re keen on what we’re doing, please get in touch to tell us. There’s nothing like a few words of encouragement to get our volunteers to put in even more effort 🙂

A non-AWS arena for beginners.

Each of the robots we’ll be putting into the kit will all have a key strength but also deliberate weaknesses in their designs. For example, OpenDozer can push any other robot out of the arena once it gets behind them – but if it gets tilted up a little then its wheels leave the ground and it’s helpless. OpenFlipper can flip anything out of the arena… but it’s not fast enough to run away from OpenDozer. Careful design of these robots means that all the participating roboteers will have a similar chance at victory. That’s more fun for everyone – which is the important thing when you’re using them to encourage others to get involved in AntWeights. They’re also designed so that – if run in a closed arena with no drop-offs – they will rarely become stuck or stalled. So the organiser won’t have to keep dipping into the arena to rescue the bots.

Too many prototypes?

All our robots will be constructed to AWS rules. But don’t worry, no-one is going to put these sweet little softies into a real AWS comp to get minced.

The Radios

The radio kit uses the ubiquitous nRF24L01+ modules. In our set-up they’ve a reliable range of about 5 metres and the receiver automatically goes safe when out of range. Everything is programmed via the Arduino IDE – so it’s easy for beginner programmers to get into.

The transmitter circuit builds onto a single board complete with two Xbox-360 control knobs to give full proportional control on four axes plus two ‘click’ buttons for weapon control. It runs from 4AAs for many hours. We’ll be offering a 3D-printable TX case and a quick-build laser-cutable one.

When first turned on, the receiver is in ‘safe’ mode with all motors and servos idle. Nothing on the robot will activate until one of the transmitter buttons is pressed for the first time. So plugging in the battery won’t result in the robot suddenly moving its weapon. The receivers have programmable servo protection, which prevents a servo burning out if a mechanism is jammed. The built-in motor controller has over-heat protection so stalled motors shouldn’t damage it. Maximum constant current output is about 1.2A for each of the two motor channels. And of course there’s input voltage polarity protection. The receiver also includes programmable battery voltage warning and shutdown – which can be suppressed via a switch on the transmitter for ‘real’ battles when you really wouldn’t want your robot to go into idle-mode just because the battery is a bit low. The receiver runs best from a 2S LiPo and servos must be HV type – we use Corona MG929HV’s which are great little servos for under a fiver. The receiver can also run on 4 or 5 alkaline AA. The receiver board is 24mm square and 6mm deep.

The larger (lower) double-sided SMD board is less than an inch square. Incredibly, one of our volunteers soldered this one – and a dozen more like it – by hand. Once prototyping is finished, though, we hope to be buying ready-populated receiver boards. Motor outputs are top-left, two main servo outputs are top-right, and power-in is top-middle. The USB is used only for programming and debugging the code. The upper (smaller) board is a ready-made mini nRF24L01+ module.

Unlike conventional RC kit, all the individual model setup parameters are held in the receiver. This means that any transmitter can be bound to any model and control it without needing a special setup – ideal in a club environment. The standard software – which is fully customisable – offers skid steering with optional expo on throttle and steering. There’s optional trim on steering. The receiver has ports for two servos (and more can be attached if required) each with independent trim, throw and idle-protection settings. Servos can be attached to any of the spare outputs from the transmitter – joysticks and/or buttons – with either proportional control or set to action a pre-programmed sequence. For example: flip-pause-return-delay-idle. Up to 63 receivers can be uniquely bound to each transmitter.

Battery, servo, and motor connections can be via 0.1″ header pins – suitable for standard servo plugs and for commonplace JST-type connectors – or by direct soldering, as preferred.

A DSM-compatible version is in the pipeline, so you’ll optionally be able to use a Spektrum/Orange transmitter, too.

What Can You Download Now?

Well, at the moment, not very much. But it’s coming soon. The downloads/links will include all the plans and instructions you need to build an entire arena and the robots which go into it.

To see what’s available so far, please click here to go to our downloads page.


To keep things fun for all club members we’ll be running two levels of club competition here at Mechanical Cat:

  • A full-on AWS-rules contest which any robot can enter provided it meets the official AWS rules.
  • A ‘play-all-day’* contest which will be under identical rules except that the arena will have less drop-off perimeter and the contest will be limited to robots which have neither crushing nor momentum weapons – so no spinners, hammers, disks, or crushing jaws. Nor – should the AWS rules change to allow them – will entanglement weapons be permitted.

We reckon the ‘play-all-day’ contests will bring out far more inventiveness in our members and – although the actual battles might be less spectacular – the resulting robots will turn out to be much more interesting because they won’t have to focus on defensive armour at the expense of creative mechanisms.

OpenFlipper: Our first-ever AntWeight. Budget HV servo to flick the flipper. 300rpm motors drive 25mm silicone-tyred wheels. Quick-change 300mAh battery. Receiver re-programmable in-situ. Easily flicks itself right-way-up if inverted. 120g. 100x97x35mm.

The receiver has several optional inputs for a huge variety of detectors which could be used to let the robot sense its surroundings. So in both contests we will allow – indeed we’ll strongly encourage – roboteers to program the Arduino ‘brain’ that’s built-in to their robot receivers to automate as many functions of their robot as possible. We may even try for fully automated robot contests – perhaps along the lines of the MicroMouse ‘Sumo’ class of robots.

And, of course, some of us will be attending AWS meetings with our robots, to take part in national contests.

*So-called, because the robots can run all day long without destroying each other. This is exactly the type of robot that we’ll be including in our downloadable kit.

Other Radio-Control Projects

We’ve got plans to mod the RC system so that a ‘master’ transmitter can start and stop all the AntWeight robots. This will be ideal for busy demo-day environments, where visitors are offered the chance to drive a robot for a few minutes at a time.

We’re also working, in the background, on morphing our AntWeight RC system into a super-low-budget 40-channel RC package with the transmitter controlled through a USB link to a PC. This is something which could be ideal for projects with really complex control requirements such as animatronics and snake-bots. Watch this space.

But Please Remember That Mechanical Cat is Not Just About Antweights!

For those new to Pembrokeshire Robot Builders Club please remember that we don’t just do Antweights. So if you want to build something robotic – whatever it is – we’ll be happy to welcome you into the club and help get you started. The best way to find our more is to come and meet us any Wednesday evening from 5pm to 8pm here at FabLab.