Ipromised to update yo on our tunnel.
A little back ground incase you did not read the original post.
We could not spring for a factory built, so we got some big 10 foot iron rings donated from the power company, the giant ones that holds big wire. We cut out the spokes so we had four big heavy rings. These were too big to put in the standard bike rims and too heavy for the motors we tried. We built a frame out of wood and set the rings on big metal rollers. this tunnel is 2 10 foot sections divided in the middle. We used 4 tread mills (2 would not do it) one with each ring resting on it. It actually runs very smooth. On the 4rth night of running this thing for about 5 hours a night, one of the treamills belt wore out, it split, so we just moved the part of the belt that was good over to where the ring is and it is back uo. The other tradmills appear to be wearing a little as well, so that is the weak link in this plan. We knew it was not perfect, but are hoping it will get us through this season. We are thinking of a way to just take the belts off and maybe put some grip tape or something and put the roller up to the ring.