for anyone who wants to give it a whirl, here is how I built our sidecar. It is based off the Scandinavian side bike design , which is not available outside Europe, and expensive.
For starters the frame mount on the bike is made from a piece of channel that is cut and bent to hug the frame, and extend past the wheel bolt. Taking into account foot size on the pedal and having the attachment points far enough apart for 80 lbs hanging off the side. It attaches under the frame like the kick stand and at 3 other points on the frame with u-bolts. The attachment points are air cylinder rod ends, and the vertical plate piece is just some scrap I had.
For starters the frame mount on the bike is made from a piece of channel that is cut and bent to hug the frame, and extend past the wheel bolt. Taking into account foot size on the pedal and having the attachment points far enough apart for 80 lbs hanging off the side. It attaches under the frame like the kick stand and at 3 other points on the frame with u-bolts. The attachment points are air cylinder rod ends, and the vertical plate piece is just some scrap I had.