https://www.youtube.com/watch?v=nq7h6nQmKoM

This is a carpet mill I built some years ago. The video looks like my camera guy (12 year old son) was running with her.

She opens up and can go all out, but each step is still driving the mill. I like it a lot.

I just built a slat mill as well. Like you, I think I will make another stab at it in the coming months. I used skate wheels instead of roller wheels and the wider running surface provided more drag than I anticipated. The material I used to bolt the slats to is a bit flimsier than I would have liked, or more flimsy that I expected. It was a neat project. I will try to get a video posted the next day my son and I are off at the same time. EWO