I looked in the dog world for someone to build the cart I have in mind but learned that such people are few and far between (basically nonexistent). So, I guess I'll have to build it myself, or at least learn how to put it all together so that I can explain it to someone else who will do the building for me.
Here's a bird's eye view: http://tinyurl.com/348kuf
The same but with the parts labeled: http://tinyurl.com/38mhak
Some measurements: http://tinyurl.com/2soq6q
More measurements: http://tinyurl.com/3ygeug
Here's a picture of a dog and scooter I got from the web. I drew in the harness, shaft and hitch that I have in mind for my setup: http://tinyurl.com/2ts8qj
Here's the shaft in "motion": http://tinyurl.com/2mb8ar
Here's a weird bike I found on the web that has the basic shape of what I had in mind for the cart: http://tinyurl.com/2l436c
I've erased the gears, pedals, etc. and drawn in the steering mechanism I have in mind at this point. (That would be two chains hanging down for my feet to set on.) I think that would give me the traction I need and would be lightweight. I'd like the option of a steering handle so I can steer with my hands if I don't want to steer with my feet, or if I need to get off the cart and help the dogs up a hill and steer.
Weight is extremely important for this cart. I have a really bad back so the bike will have to be lightweight and come apart. Maybe the wheels can come off, the seat, and the shafts, leaving just the frame.
I can't take nice, long, leisurely walks because of my back so this cart would enable me to take those walks. No running, just walking. The cart will mostly be on dirt roads. I'd like a future version to have off-road capabilities.
In the diagram I have the back wheels under and a bit behind the seat so their legs and tails don't get caught in them. They would be fairly close together, providing a bit more stability than just one wheel and allowing the cart to stand on its own without the dogs hooked up to it. The dogs themselves will sort of act like training wheels on a bike when they are hooked up.
I don't want my butt more than 12" off the ground. That would make the back wheels less than 12". I don't know how tire size affects their ability to pull me on gravel roads. If small tires would make it too hard for them to pull me then I'll have to make the tires bigger and change the design. The front tire should be far enough out front that it won't be in the way of their legs.
The way the cart is designed now, their backs make very convenient arm rests. :-D
I haven't figured out a brake system yet, other than telling them to stop and using my feet if needed.
The hitch line that connects to their harness would have a quick release snap in case they had to be freed quickly, like if a strange dog came up causing trouble. Their leashes would always be attached to their regular collars too.
I am thinking it would be best to have a hinge with a tension spring of some sort on the shaft. Otherwise the shaft could poke into their backs when stepping up on something like a curb. Hopefully the diagram I drew will show how it would move up and down with the dog as needed, with the middle drawing being the neutral position. The tension spring would cause it to always pull slightly upwards at all times. If the dog has to step down then the weight of the dog will pull it downwards with him/her, then it would go back to the neutral position. It wouldn't be able to go forward, backward, or sideways, just up and down.
I am thinking that the seat should absorb the bumps. I don't know what type of seat I want yet. I have a few ideas though.
I don't know how much distance can be between the front and back wheels and still safely support my weight. From the looks of that bike I linked to, it looks like I won't have much to worry about.
So here it is on paper but I don't know if it's structurally accurate and I certainly don't know how to make it real. I am actively looking for someone to build it for me so if you can help with that then please email me at hotmail.com and if you have any suggestions or thoughts or comments or whatever then do post them here. I don't know anything about designing a cart like this.
Thanks for looking,
Miztiki
Here's me by the way: http://tinyurl.com/2pg6jc