How to put wheels on a chicken tractor

This video is a follow up video on how to build a chicken tractor. If you have a coop without wheels, you could use this setup as well. All the materials should cost around $60. That includes the wheels. I use 6 8inch bolts, 10 nuts, 12 washers, 4 lock washers, 2 2 1/2 foot 2x4's, and 2 wheels. Everything was a 1/2 inch in diameter. This is the 3rd chicken tractor I have made, and it is by far the easiest one to move. I move it up a hill towards the end of the video. I can go forward and back, and the wheels stay up. If you like the setup, please share it.