Robot Attack

It was nice Utopia world where robots and humans lived in peace. The great world is over because the robots started attacking the other group of the population. Our small tiny hero must prevent more killing. He activates a defensive tower where you build several cannons which can be improved. My try ended terribly. When I saw that the TD game offers walkthrough I knew that something is wrong and it won't be so easy. I have tried several strategies but I couldn't get pass the third wave. I hope you have more luck.