Protecting Earth - With Rubber Balls

A lot has happened in the last few weeks. Sputnik has a new paint job - all silver and sparkly, we've fitted the Pixy2 camera (and got it to work to some extent) and decided to finalise our solution to the Space Invader challenge.

When we applied for Pi Wars back last September, we had planned to use the balls to knock down the target. The idea was to build some kind of ball kicker powered by a solenoid or servo to propel the balls towards the target.

Then - when we went through a couple of iterations of motors, we thought we could use the spare motors to make a Nerf bullet launcher. We built a prototype with lego. Everyone stood back for the first lauch, only to see the bullet struggle through the lego barrel and drop to the floor. Looking at other posts the motors being used are running at something like 1800rpm - so our little micro motors were never going to make it. So that idea was shelved.

We then built a lego kicker - using a small servo motor. The prototype didn't quite have enough power to move the balls in a straight line.

At the time, we were still on the reserves list, so there wasn't a great worry. Then when we got the call to take part, we realised we were going to have to work out something - however primitive.

This is what we came up with:

Sputnik with ball launcher and laser sight

It's a Lego contraption that is used to aim the ball with the help of two extending arms and a laser pointer. When the 'X' button on the controller is pressed, the robot launches forward. A spring loaded arm at the back of the device is pushed back by the sudden momentum and helps propel the ball in a true line.

That's the theory anyway - but does it work? Well - actually it's not bad, We ordered the balls used in the competition for our testing. It's takes some finesse to line up with the ball without knocking it forward, but once 'captured' it can be manipulated left and right to fine tune the aim. Because it was difficult to aim using the current controls, we decided to use the R2 and L2 triggers on the controller to spin the robot very slowly to the right or left to help out here. Here's our attempt at annihilating an alien invader - well, trying to hit a small box with a rubber ball:

The aim is true about 2 times out of 3. That's using the longer 1.5m distance. However, reading the challenge more carefully, we realise that we only have 5 minutes for all 3 rounds. That's 20 seconds per ball. We've timed it and can get it down to about 16s - but it's going to be tight. We may have to
accept that we'll probably run out of time and concentrate on accuracy.

It would be nice to come up with a more advanced solution with a nerf gun or similar projectile launcher, but we have been limited by both time and ability. We need to just call this challenge complete now and move on to the Hubble Telescope Nebula challenge - which is the only one we can't do now.

Time to take off the lego and put on the Pixy2 ...