Make a notch in the rim of the two tin cans (note: In the picture I used foam cups instead of cans, because I didn't have any cans, but this does not work as well.)
Rest the axle pins in the notches of the cans.
Although your solar motor might be ready to use now, it is a good idea to balance test it first. Give it a spin. If it looks like it if heave on one side, add weight (pins, small brads, etc) to the opposite side until it is balanced.
Note: add the weight to the Styrofoam Back disc, Not to flywheel.
You are done!
Put the whole assembly in the sun - if everything is built right, if will begin the rotate. The more balanced it is, the faster it will spin.