Metal Construction
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The next model was a tractor with timber trolley in the scale ca. 1:8; it was built up in 1997. The specialty of this model was a solid, multiple supported swing axle. Also into this model was built a drive and a radio control with all steering functions.
First again there was the problem to find adequate wheels. With the MÄRKLIN tractor wheels the model would be too small to install the drive and the radio control. Thus wheels of the CONRAD electronic company with a diameter of 160mm were used. As front wheels the existing 100mm wheels came into operation. The power train from the 4mm axles to the large rear wheels here is anymore critical as at the nostalgic motor-lorry. As a result shortly after the first gear wheel (MEKANIK, modul 1) fell victim to the strong torque. But that was not the end of it: Even if all components withstands the torque, anytime the axle slips in spite of the locking screws; therefore the axle had to be flattened at the fastening points. Another challange at the small construction of a tractor is the integration of all necessary components. Therefore for instance the accumulator had to be mounted into the "second floor" above the steering servo and the radio control receiver.
Because of stability the swing axle was backwards triangular reinforced; altogether the axle had a quadruple bearing and was very warp resistent. Attention should be paid to the steering of the front wheels: At a simplified Ackermann-steering (see "Other Projects") the steer angle changes a little bit with oscillation (as much as during movement of a conventional damping). At a model it is not essential to compensate this, but itīs possible to minimize. By graphics one can show that the effect of the pendulousness to the steer angle is minimal if the pivot point of the wheels is on the same level with the swing axle bearing. As drive again the proven MEKANIK motor was used. Since the rear axle of a tractor usually is without damping the construction was very simple. To avoid jerky forces the motor had a counter bearing consisting of commercial miniature rubber dampers. Because of the missing differential also at this model only one wheel could be driven. For the tractor was constructed a timber trolley, which was able to transport wooden sticks up to 1m length. To realize a slightly movable steering the front suspension was provided with a roller bearing assembled from 4 small rollers and 2 round plates. The total length of the vehicle reached 1,6 meter.
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