If you have a black walnut tree (Juglans nigra), hardy in U.S. Department of Agriculture plant hardiness zones 5 through 9a, the easiest way to collect the delicious nuts is to wait for them to fall. Even if you don't plan to eat them, though, you still have to pick up fallen nuts or you won't be able to maintain your lawn. Walnut trees can be prolific, and picking up the apple-like seed pods is hard on the back. You can make your own simple tool to accomplish the task without so much as bending your knees.
Cut a 4-foot length of 2-inch PVC or ABS plumbing pipe, using a hacksaw. Sand the edges of both ends of the pipe with 120-grit sandpaper to smooth burrs and etch the surface of the plastic.
Trace one end of the pipe on the plastic lid from a 1-quart yogurt container, using a felt-tip marker. Cut around the tracing with a utility knife.
Attach the plastic circle to one end of the pipe, using duct tape. Wrap the tape around the edges of the plastic, but leave the center uncovered.
Trace a cross on the plastic with the marker, and cut along the lines with a knife, ending each cut about 1/4 inch from the pipe. The purpose of the cuts is to create four flaps that make an opening large enough for a walnut.
Use the tool by holding it vertically over each walnut and pressing the end with the plastic cover into the ground. The action forces the walnut past the flaps, which should be rigid enough to prevent the nut from falling out. As you continue to pick up nuts, they will stack up inside the pipe and eventually start coming out of the top end. Transfer them from there to a container.