Last before Cambridge

So this is possibly our last blog entry before we're off to Cambridge with Zyderbot, ready or not. I'm sure we'll take part in everything anyway but this is where we're at right now. 

So we had to make a video, I suppose we could have done it weeks ago but even though it's one of the challenges, somehow it doesn't feel like it. This blog has been going since last September, but even so, it still feels more real. 

Two of us got together in the kitchen with an old camera (well, old for modern times, it was still digital!!!)  and with a basic script took turns to operate the camera and do some impromptu words about Zyderbot. We aren't natural publicists so we're a bit awkward, but it's done.

The video became an explanation of some of the key points, with added picture within picture to provide voice over explanations of key points, this picture showing the emergency fuse to prevent magic smoke emissions.

While it's a competition and we want to compete in all the challenges, we have to enjoy doing it, and the real competition is solving the puzzles we're given. The rest of the pictures here are all from the video of some things we've learnt.

Nerf guns and Stepper motors

Being geeks we had nerf guns, but adapting the mechanism for use in PiWars turned out to have a range of issues. But here it is in all its chaos. Eventually all that is used from the gun is the flywheel acceleration module, and the dart magazine.

We had some fun with the aim of the gun, and have fitted a recycled barrel to increase accuracy. The barrel was originally a croquet mallet handle, which then became a battery holder in a previous Zyderbot iteration, and now a nerf gun barrel. You can just see a cat toy laser clipped on underneath.

The flywheel module of the original gun was easily unscrewed and was easy to remount.

The trigger mechanism wasn't so easily recreated and we ended up using a stepper motor to push the darts into the flywheels. 

Lesson learnt, do not power stepper motors continuously when not in use. So it was left powered on, heated up and shortly the plastic mount for it melted. Replaced with a metal mount and a change to code in a float state when not actually in use.

Magnets

We use a lot of magnets for quick assembly and disassembly of Zyderbot between challenges. Here is the main arm which is reused between the Eco-Disaster and Zombie Apocalypse challenges. The base is attached to the robot rear using a pair of magnets at each corner which gives a very secure base.

 

Four magnets on the arm allow for holding the zombie gun and barrel handling attachments

Four on the attachment line up 

And fully assembled with four matching magnets it's a secure joint.

The nerf gun similarly has four matching magnets

And so has a very secure platform.

Lesson learnt. You don't need four matching magnets for everything. The magnets are strong enough to hold using just a metal washer on one side and magnet on the other. We fitted four pairs to the battery box and now need a crowbar to get it open. They're also not always cheap so it costs twice as much!

Barrel Handler

One of the things we want to avoid in Eco-Disaster is to have barrels rolling around the arena. Partly because they'll be difficult to get into the end zones, and also because they'll potentially get caught under Zyderbot and need a rescue. 

Consequently, last minute mods to the barrel handler to add a plough to push barrels away that accidentally get in the way. This means not lifting the barrels very high, but then also not having to worry about dropping them on another barrel, though stacking them would be an interesting challenge (a la toys). We've also fitted a rear bumper to do the same thing.

Configuration

Zyderbot has a set of 8 dip switches on the rear which allow easy configuration between challenges.

Also shown in the picture is the battery monitor display, the rear light and the stop/start button. The rear light also doubles as an information display. For the Pi-Noon challenge we'll be covering this with a magnetically attached plate to protect the settings!!!!

Ultrasonic sensor

Lots of us will recognise a HC-SR04 ultrasonic sensor, so we couldn't miss one off, it's very easy to use and adds a bit more of a feature than a 5mm square laser sensor on pcb, though we're using one of those as well!!! Might come in for barrel detection as well.

Lighting

We have very little idea of what the lighting will be like on the actual day and most of our testing has been done in very variable conditions, so having a pair of headlights on the robot helps a lot in colour and line detection.

It's also part of the robots image, we can't have a lightbar because of the attachments but these will work well.

Might actually do a blog of the weekend but we'll see how excited we are :) 

Well that's this bit done, just the competition itself, then back to building and demonstrating other robots, but I'm sure we'll find a place for Zyderbot!

Tuning!

 Tuning!

So we build solutions, they should work, and then the real world gets in the way. 

Lava Palaver progress

We'd gone for a camera sensor for the Lava Palaver challenge, not because it was a better option for following a line, but because it was automatically immune to the hump in the course. However, this threw up new issues. The competition course is 7m long and painted black, the only surface available for testing is a light wooden floor which makes for very poor contrast.

 Early testing was plagued with phantom readings from reflections which confused the robot, so testing moved to using a black line instead, with the intention of switching over to white for the competition day. This was much more successful, but space is a limit again. To make a test worthwhile, we're going to have to go for a bigger course outside, using a long roll of black art paper with white electrical tape down the middle and hope for dull days!

Illumination was oddly a very important feature. Off the shelf line follower attachments tend to be IR sensor based and have built in illumination which tends not to be noticed, but for the camera, even illumination is essential to get good contrast for the line, so the robots headlights have to be used to light up the track ahead, together with an overhead light illuminating from above. 

The result is a fairly simple bit of code at the end, but beneath it is a lot background code doing the heavy lifting and interfacing. 

One of the items outdoor testing might help with is coping with bright sunlight and shadow. Watching the competition from previous years, it's obvious that this can have a detrimental impact on robots using optical sensors so we'll be looking at that. It's hasn't been done yet but we'll be experimenting with a sunshade for the robot to give more even lighting for the camera and hopefully reduce errors.

Zombie Shooting

For the Zombie Apocalypse, we've had an idea to use a butchered standard nerf gun which looked very promising out in bits on a table, see an earlier blog post, but we discovered a weakness. Using the servo method of pushing the nerf pellet into the gun worked a lot of the time, but then would jam the gun requiring it to be dismantled to clear the jam, it wasn't suitable for the competition. This held us up for quite a while but an obtuse solution using a stepper motor and a rotating cam came to the rescue, so now we're back in business.

The video shows the cam operating and firing off a magazine of pellets. We then got a cat laser toy and pressed it into service to help with aiming, now how many competitors will be aiming at butterflies?

As the video shows, the gun fires to the left, a bit more work to do but on our way.:) 

Minesweeper

Again, this is one we had a solution to some time ago, but when we come to use it, there's a surprise for us. We're using an overhead camera, but processing the image in memory leaves off a lot of the arena, a 'feature' of the camera.

 The image was always going to be distorted but missing bits is a problem we haven't time to overcome, we'll just have to code round it. This means that the robot will have to search for the red square sometimes instead of just being able to see it and move to it. 

The algorithm for this will be basic, something like the following.

Just how accurate the movement will be isn't known, we were expecting to just move to the red square wherever it was, but this now requires some idea of where the centre of the arena is. Only testing will tell. We're doing this challenge on mecanum wheels. As the arena is 4 x 4 matrix, all red squares will be within it and so a map can be built of the arena based on squares that have already been red. Will this be good enough for the minimum 20 moves required we'll have to see. Anyway, signing off with an errant robot which finds it's square, and then ignores it, ho hum.