I’m thinking about making a Pedalo (here) for fun but I can’t figure out what to use for the wheels. Cutting my own out of wood would be challenging to make them all the same size and a circle. I looked at lawnmower wheels and they either concave or where I would put the bolt, it’s uneven. Any suggestions?
For those that might have this is it worth trying to make it?
Get one of those drill bits that are circular and get one of the right size. That’d be a perfect circle and if you pick the right wood, it should work okay!
To cut 3 same size circles out of wood is fairly simple, you need to make yourself a carpenters compass: Basically you need a thumb tack, a pencil & a length of string:
you swing the pencil around the thumb tack, tied to it with the string. The pencil is then a constant distance from the center point (tack), giving you a perfect circle. Then use a jigsaw or a hacksaw to cut around the line, making sure you leave a gap and sand it down to the line, making the circle exact.
If you are using some kind of rubber ‘tyre’ fixed to the outside, then the circle doesn’t need to be as exactly cut out, any small flat spots will be cushioned out.
Loose.
Something like this:
or do a rough cut out, stack all three together, then spin them on a lathe or motor or anything that will spin them while you hold a rasp or sureform to the edge…that will make them perfectly round.
looks like an ultimate wheel with training wheels 
The commercially made versions of those things I’ve seen have ranged from lousy to terrible construction. Lousy will hold up fine under light and occasional use. The terrible ones will rip up as soon as you try to turn on concrete (instead of a gym floor I guess).
So if you make your own it stands a good chance of being far more durable. You don’t need three disks, only two. Make a crank that zig-zags between the two disks. Of course it has to be pretty strong.
Or, for a slightly more interesting ride, put the two disks about 6" apart and put the pedals on the outside. Then you can just bolt them together with pieces of pipe in between, or similar.
The best way I have found to cut uniform perfect circles is to use a band saw. I clamp a piece of plywood to the table of the saw and put a nail at the distance from the blade of the radius I want to cut. I drill a hole in the center of the piece and turn it on the axle made by the nail. It turns out a perfect circle. and each pice made on this jig will have the same diamaeter.
I found this and so I might try to make this one, I’m not sure yet. I like the idea of sanding down to the pencil line that sounds like it could work.
That is like a cheaters ultimate wheel! Cheater!!! 
well you have to start some where…