Welcome to my first Instructable!
I got the idea to make this while teaching a unit with a Junior Kindergarten class about 'Things that Move'. We had been talking about how we can use the energy from moving things to help us do work. I brought my own kids to the school on a weekend to try to come up with a working prototype after an afternoon of mucking about in the Makerspace we managed to put something together.
Step 1: The Build
I pulled the tires off of a bicycle that I had found in the trash and cut a couple of circles on the router table out of some MDF. I didn't take any pictures from that step but here's a short video on YouTube to show you how if you need.
I drilled a few small holes to attach them to the spokes of the wheels with zip ties. Then I drilled the holes all the way around the outside for the dowels. I cut the semi-circle on the scroll saw to make the hinged closure.
The frame is built from some pieces of recycled 1x4 from some old shipping crates and a 2x2 that I cut from a pallet.
Finally, I drilled a hole in the end and drove a carriage bolt through it to make a hook to attach to the bike.
We designed it so that it would fit one of those big 64oz. containers for protein powder. That would be where we put the ice cream mixture and the ice and salt.
Step 2: Filling the Container
We filled the container with alternating layers of ice and salt. We didn't really measure it out very accurately. We just sprinkled a handful of salt over each layer and it worked out fine. Once it was about a third of the way up, we put in our ice cream mixture. We used a water bottle and a very simple recipe--a cup of whipping cream, a cup of chocolate milk and a tablespoonful of sugar. Then we put the mixture into the big container and continued layering the ice and salt around it. Once it was full, we put it into the bike trailer and used some duct tape to hold it shut.
Step 3: Churning
We hooked the trailer onto the back of a tricycle on the playground and the kids took turns riding around churning the ice cream.
After 20 minutes, there was a thick layer of frost on the outside of the container.
It came out a little grainy, but frozen well-enough to call it ice cream. It was pretty tasty and the kids enjoyed it, but I'm sure there's plenty of room for improvement.
Step 4: Reflection
The trailer was a bit rickety afterwards and a couple of the dowels came off while I was carrying it back to my room but it was a fun project and as a proof-of-concept, it was a big success.
For the next version, we will want use thicker pieces of wood in place of those dowels. I'm also thinking that a container for the ice cream mixture that isn't perfectly round might slosh around a bit more as the drum rotates and make for slightly less grainy ice cream.
But plan at this point however is to throw this project at some older kids and see what other improvements they can come up with. I will be sure to post back when it's done.
Thanks for reading!