I'm just about finished with my motorizing project - a yard cart with 16" wheels. The most difficult bit of engineering was coupling the motor to a hollow hub wheel. I've not seen any detailed descriptions on how to mate the Wheelez wheels to the motor either. Since you can have access to a welder, then I'd suggest that you simply weld a sprocket to the inside hub of one of the wheels. If you wanted to get really clever, you could drive BOTH rear wheels of your wagon through a jack-shaft with dual sprockets.
Sometimes the Electric Scooter Team is a bit slow in responding. Happy to discuss this outside the forum if you like. Email me at ltcdfancher at woh dot rr dot com.
To attach a sprocket onto a cart wheel like that there are a few methods that I know about. One method is to use steel pipe as standoffs to attach the sprocket to the rim. The steel pipe can be welded to the rim, or holes can be drilled in the rim and bolts can go between the rim, standoffs, and sprocket. Of course this will take a slight level of precision to get the sprocket centered on the rim so it is true and does not wobble. I know that many of our customers have successfully attached sprockets onto cart wheels this way though. If I were to do this I would select a pipe size with an ID that is just big enough for the sprocket bolts to fit into, then weld the pipes onto the rim, and then drill out the rim where the pipes are and use a through bolt to hold the sprocket onto the rim with the pipes in between acting as standoffs.
For the rest of the build since the cart will carry a heavy load and has to go up and down hills I would use one of our large 36 Volt 600 Watt gear motors. And to make sure the wagon has enough battery capacity for the evening I would use three 12V 35Ah batteries for the battery pack. We have a kit with these parts in it which is our item # KIT-149. Here is a link to it: http://cart.electricscooterparts.com/ProductDetails.asp?ProductCode=KIT-149
We can modify this kit in any way that you would like, such as with a different throttle, batteries, charger, etc. Please let us know if you would like any changes made to it.
As far as the gear ratio goes that is one of the most important aspects of the build. I imagine that you want this wagon to go walking speed which is around 3-4 miles per hour. I will work on a gear ratio and sprocket size plan for this speed.
Here is the gear ratio that I found will work with the 36 Volt 600 Watt gear motor and 16" wheels.
The gear motor has a 10 tooth sprocket already on it for #420 chain. 60 tooth sprockets for #420 chain is a very common size for go karts and mini bikes and available at almost all online go kart parts stores. The 3.82 MPH top speed will be a little lower when the wagon has a load on it so I would expect it to be around 3.5 MPH which is the perfect walking speed.
Please let us know if you have any questions.
KIT-149 includes three 12V 35Ah batteries. I would expect the constant run time to be around 3 to 4 hours with this size of battery pack. The more hills that the wagon goes up the less run time it will have, and the more flat ground the wagon is driven on the longer the run time will be.
I have the exact same wagon, and I was wondering how your project turned out.