[ngreen]

How I see it adding the 2 lbs behind the back tires might not help but rather hinder more. When you climb stairs you want your center of gravity to shift forward to make it the easiest. Your best bet would to get it so those front wheels will come down and be touching and have enough traction to pull the back wheels up. That how I see it. Reduce pressure may give you enough traction to drive up the step but it will still be hard for it. Or add an arm that you can throw forward with weight on it so that it will put you center of gravity more over your from wheels when you climb. But I don't think the adding weight behind the back wheels would do you a lot of good.

We actually started with an eight wheel design with the center wheels like paul descibed. We ditched the center wheels and are instead using two plastic "sleds". It makes it up a lot smoother and they weigh like half a pound together. We still use non-powered wheels on the front to bump us up onto our front wheels. The sleds lift the robot so that the back wheels hit the edge 2 inches higher. It still takes momentum but is a much smoother transition. I would reccommend trying it by taking two pieces of a strong plastic and clamping them on between the two drive wheels . We found it's better if the slope is fairly flat or even a little more sloping downwards to the front wheel. It should take a couple minutes to try out. And if it doesn't work just change it.