Mini Mouse on usedbytes:Blog

Pi Wars: Post Mortem

Sun, 31 Mar 2019 20:20:41 +0100

Pi Wars happened! It’s over! I can start doing something else with my life!

I had an awesome time at Pi Wars today and yesterday, with Mini Mouse performing pretty solid attempts at all of the challenges. I ran into a few hiccups on some challenges, but far outperformed my expectations on others.

Overall, I placed 3rd in my category, and am really happy to have been awarded first place for this blog, and Artistic Merit (for being “beautiful on both the inside and the outside” - thanks Rachel :-)

Pre-Competition Status Report

Thu, 28 Mar 2019 20:58:21 +0000

With two days to go until competition day (only one day for schools and clubs!), I thought I’d capture the status of Mini Mouse, for posterity and for something to compare against in a Post-Competition Post-Mortem.

I’m quite happy with where I’ve got to. The autonomous challenges are all working mostly reliably in practice runs, and the performance seems to be competitive. Of course there’s no guarantee that it’ll perform “on the day”, but I’ve done all I can at this point!

Autonomous Challenge: Hubble

Wed, 13 Mar 2019 16:15:56 -0700

The Hubble Telescope Nebula Challenge (previously Somewhere Over the Rainbow) is one of the autonomous challenges, requiring the robot to visit the four corners of a square arena, starting from the centre. In each corner, there’s a coloured board - and for maximum points the robot must visit the corners in an order specified by their colours (Red, then Blue, Yellow and finally Green), as quickly as possible.

My overall strategy for this challenge is to spin on the spot at the starting position, to identify where each colour is. Once all four corners have been identified, they can be visited in the appropriate order. Originally, I was also intending to use the camera to make sure the ‘bot stays on-course whilst en-route to the corners, and to detect when a corner has been “visited”. Ultimately, I’ve found dead-reckoning using the IMU and counting wheel rotations is reliable enough, and so I’ve skipped the added complexity of using camera feedback for the actual “visiting” phase.

Setbacks

Fri, 08 Mar 2019 18:20:44 +0000

Three weeks ago, I got a basic implementation of The Hubble Telescope Nebula Challenge working, which made Mini Mouse’s code “feature complete” from the point of view of entering all of the autonomous challenges.

Honestly, I was pretty darn happy. All three challenges were working well enough to be “competitive”, and with more than a month to go until the competition, all that was left was optimisation. So, I spent a week doing rapid-fire blog posts .

Mini Mouse's Armament

Wed, 20 Feb 2019 20:37:14 +0000

Now, irrespective of personal views on arming robots, unfortunately one of the Pi Wars challenges requires¹ that we weaponise them. For Space Invaders we have to be able to knock down as many targets as we can (up to 5) from 1-1.5 metres away.

Plan A (top)

This challenge has caused me a great deal of head scratching as I sought out the right option for projectile launchers for Mini Mouse. For Bot Matrix the plan was dual-wield repeating rubber band guns - so that was my starting point for Mini Mouse too.

Edge Detection

Tue, 19 Feb 2019 20:23:05 +0000

Identifying edges is one of the key “features” of the human vision system. Our brains have evolved to identify edges and it’s one of the things which lets us pick out different objects in the world. If we want to teach our computers to see, Edge Detection is one of the key tools needed to reach that goal (at least, according to “classical” methods. Things change with Deep Learning).

Autonomous Challenge: Blast Off

Sun, 17 Feb 2019 19:52:08 +0000

Blast Off: the Straight-ish Line Speed Test is, to my mind, the easiest of the three autonomous challenges in this year’s competition. As such, it’s the one which I started working on first.

The task is to get from one end of the course to the other as quickly as possible. There’s effectively two feasible options:

Follow the walls
Follow the white line

Given that I don’t have any side-facing sensors to follow the walls, to me the easiest option looked like following the white line.

Mini Mouse's Software

Sun, 17 Feb 2019 11:43:26 +0000

Before I dive in to details on individual challenge implementations, I thought it would be sensible to describe how the software on Mini Mouse sits together. Some of this information is duplicated in We’re in, but there’s more detail here, and things have evolved since then.

The diagrams on this page are created with graphviz (or more correctly, dot), which doesn’t give the prettiest of drawings, but does stop me wasting time obsessing over layout.

Final Hardware

Sat, 16 Feb 2019 22:03:44 +0000

It’s been a few frantic months of robot building between my last post and now, a decent portion of it being focussed on finalising the chassis. Since around September I’ve had my prototype chassis working, which has given me a great test-bed for software implementation testing and debugging the hardware design.

There were three main (known/intentional) limitations with the prototype chassis, borne out of a need to get it built and tested before I could finalize some of the details. Specifically:

(Quite) Robust Thresholding

Sat, 27 Oct 2018 16:55:59 +0100

Today, I’m detailing the method I’m using to threshold images for line detection. Also included are some hard-learned lessons about premature optimisation and the importance of re-evaluating your decisions frequently!

Image thresholding is the process of taking an image, and converting it into a two-color (just black and white, no grey) image. This is useful for lots of image processing algorithms - like edge or blob detection.

My initial focus here has been on implementing a white line detector for the “Blast Off” challenge.

We're in!

Sat, 06 Oct 2018 11:09:04 +0100

So last weekend Mike and Tim sent out the confirmations for Pi Wars entries, and Mini Mouse made the cut! We’re going to Pi Wars!

Doug on the Discord suggested the idea of sharing successful applications for people to look at to see if they can improve their chances next time - so here’s mine in case it’s useful.

It’s been a little over a month since my last post, but I have moved things forward a bit in that time.

PCBs

Sun, 26 Aug 2018 10:11:04 +0100

For Mini Mouse, I’ve designed two PCBs - one for motor drivers, and one for the power supply/control circuitry. These were my first boards using the open-source KiCad suite of EDA tools, having previously been an EAGLE user.

I got the boards made at dirtypcbs.com, panelising the two boards into a single 5x5 square. This is the third set of boards I’ve made with dirtypcbs, and I’ve always been very pleased with them.

Power

Sun, 26 Aug 2018 09:50:46 +0100

Every robot needs power, generally at two or more voltages - one “high” voltage directly from the battery to feed the power hungry motors, and one “logic” voltage to drive the electronics. The motor voltage needs to be able to provide high current, and the logic voltage needs to be relatively “clean” to avoid messing up the electronics with excessive noise or voltage drops.

Mini Mouse uses a 3S LiPo battery, which means it’s quite important not to over-discharge the battery, as that might damage the cells (and could even result in fire). On Bot Matrix I had a mechanical power switch to disconnect the battery, but I don’t really have space in Mini Mouse, and I also wanted to try designing an electronic switch as a useful building block for future projects. So, I need an electronic switch design which has no current draw when “off”.

Motors

Sun, 03 Jun 2018 14:55:44 +0100

Motors were the first thing I worked on selecting at the start of the development process. Given the space constraints I’m working with, motors would be a critical component which would inform the design of the rest of the robot.

Stepper vs Brushed DC (top)

In Bot Matrix I had DC motors with hall-effect encoders on the back. I used the encoders to implement closed-loop control for motor speed, and for odometry for dead reckoning. In my opinion, accurate speed control and odometry are must-have features for a robot - and so this weighs heavily in to the motor selection process.

Mini Mouse

Mon, 30 Apr 2018 19:47:31 +0100

In the past 12 months, I built Bot Matrix, aiming for PiWars 2018 (though unfortunately I wasn’t selected as a competitor). It was the first chassis I built from scratch, and I learnt a lot in the process! Bot Matrix was large (on the limits of the PiWars size allowance), and used pretty large motors and drivers.

This year’s project is a little bit different - I always fancied building a robot in a computer mouse and so that’s what I’m going for. Min(n)i(e) Mouse is different from Bot Matrix in nearly every way. Bot Matrix used a Pi 3, two dedicated microcontrollers for off-board processing, tracks, 5 ampere motors, tracks, and 3072 LEDs. By comparison, Mini Mouse will have a Pi Zero, only. All processing and control will be handled on-board by the Pi.