, Stavropol,, author photo
Ask any young opposition player what he does not like about Ural. "In the first lines" will answer: wheels. They are disproportionately narrow for a massive motorcycle. And I don’t like it either. And I decided to install the rear tires wider.
But for a wide wheel, a pendulum of appropriate size is also needed. While wondering how to make it, it seemed that the axis of the pendulum is somehow not the same. Measured - made sure: eyelets with holes for the axis are welded crookedly. Bring the frame to mind? Fuss - you won’t find it easier to make a new one.
I rummaged in the literature and found out that the duplex frame is not the ideal of rigidity. So, you need to make a spinal, and this is a spatial farm - a "relative" of farms, from which a crane is assembled. This design is characterized by lightness, rigidity and bending, and torsion.
Welded it from square tubes with a side of 25 mm and a wall thickness of 1.5 mm. As a slip used the table of the milling machine. When the frame was ready, it was scalded from the outside with 1.5 mm steel sheet - it blocked the seams and thereby added strength design. By itself, another practical advantage was formed: it became easier to wash the frame. Inside it there was a place even for a car battery (I was going to install also a starter). The steering unit, experiencing a heavy load, reinforced with a sheet of metal, and installed taper bearings from the hub of the Ural wheel in the steering column.
And only now it came to the pendulum. It was welded from sheet metal 2.5 mm thick. Geometry was strictly controlled! The pendulum and gearbox are connected through an aluminum flange welded to the gearbox. Such a design solution - the shaft inside the pendulum - did not meet in domestic technology, therefore, in order to add reliability to the weld, I blocked it with a steel plate. To prevent corrosion, he treated all cavities with Movil.
Both the frame and the pendulum were designed with the expectation that the rear suspension will be equipped with a central shock absorber. But how to choose a shock absorber? According to the rule of the lever, the force on the shock absorber when moving the point of attachment closer to the axis of rotation of the pendulum increases in proportion to the ratio of the distances from this axis to the axis of the wheel and to the point of attachment of the shock absorber. I did not find a sufficiently powerful motorcycle shock absorber, therefore I installed two Ural, but improved ones - I added half of the standard spring to each. The trick failed: even when driving alone, the suspension “punched”. I skipped the season - I decided to redo the design for one automobile shock absorber … But once a pneumatic chamber caught my eye from a grinding installation. Redid it a bit - got a real pneumatic shock absorber!..
Ask why I’m happy? Pneumatic elastic elements, unlike springs, firstly, have a progressive characteristic, and secondly, their stiffness is easily controlled by changing the pressure inside the shock absorber. After refinement, the assembly consists of two aluminum hemispheres with a rubber membrane inside, dividing it into two cavities. I installed a nipple from the camera in the upper one, and inside I glued a rubber chipper. Air is pumped here, acting as an elastic element. The lower cavity is connected to the atmosphere by a two-millimeter hole - it throttles the air entering and leaving it, thereby damping the vibrations of the suspension. This part essentially acts as a shock absorber. At a pressure of four atmospheres, the suspension without “breakdowns” withstands two riders.
Other advantages of the design: light weight, convenient, just changing the pressure in the air chamber, quickly reconfigure the suspension under the changing load. And the most significant, in my opinion, plus: the design is simple.
