FOUR-WHEEL FUN
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A one-wheel brake is all that's needed for this simple "pump-about," and that can be worked out by tacking a 1" X 9" EMT housing to the upper part of the chassis just behind the crossmember. Two more conduit sections, welded at a right angle, provide a brake handle and shaft. Once this control is slipped into place and a small spacer and stop are installed, a 27" length of strapping band is fastened between the brake shaft and crossmember, with the pulley nestled in the loop created. In practice, this arrangement works reasonably well, since a good deal of tension can be drawn on the strap through the mechanical advantage of the small pivot. But the system performs even better if the pulley groove itself is covered with a steel band, and the inner side of the steel loop is then faced with a strip of "grabby" rubber matting to act as a brake shoe.
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All the cart's wheels can be fabricated from EMT scraps and discarded bike rims, since regular spoked wheels probably couldn't stand up to the side thrusts placed upon them by a "four-footer." To mak\e sturdy units, use 1" X 4" conduit hubs, centered within the rims. For each one, cut five 1/2" spokes to length (from 7" to 7 1/8 long, depending on the rim). Lay the rim on a slab of plywood, mark its circumference, and then bore a hub-holding hole dead center. By using spacer blocks to lift the rim and spokes to the hub's midlevel, you can tack all of your parts in place first and can finish welding them when you're satisfied with the assembly.
As soon as the wheels are bolted on the axle shafts (short lengths of vacuum-cleaner hose make nice grease covers to fit over the axles between the hubs and the housings), you can complete the pumper by fastening the seat boards and the connecting rod in place. To keep the driving force aligned along the axis of the cart, the 1/2" X 29 1/2" rod has a small offset in it about 4" from the crank (rear) end. A 1"-long piece of 1/2" conduit welded to the end of the connecting rod serves as a wrist sleeve through which the driving mechanism can be bolted to the crank throw. At the front end of the rod, a 1/2" nut allows for the installation (and adjustment) of an eyebolt, or-if you have expensive tastes-a Heim joint.
With everything welded, bolted, and screwed in position, you can paint your chariot. The final step can be tricky: trying to keep the children off this four-wheeler until the paint dries!
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