UD6 Diesel Units represent the new diesel double-unit with narrow gauge and half adhesion that Firema Trasporti has developed for „Ferrovie della Sardegna„ (FdS). Each traction unit is composed of two diesel motor coaches (Mh + M) each of which is placed on two bogies. The two trailer bogies of UD6 are placed at the ends of the traction unit and the two motor bogies are in central position. This configuration allows the best mass allocation. There are two passenger entrance doors on each side of the train set. One of the two cars has a toilet, equipped for PRMs. The treading floor of the traction unit is placed at 1150mm above top of rails. Each UD6 can be coupled by one two units with multiple remote control.

Careful attention has been paid to the study of inner spaces, including ample visibility, lighting, as well as maximum comfort and functionality.The brightness inside of the train, due to the large windows, gives a sense and feeling of space to the passenger. Special care has been paid in order to define the working environment of the staff. A special cabin has been studied using ergonomic criteria in order to guarantee the highest level of comfort.

Through careful studies we have been able to obtain good visibility all along the entire train (result achieved also through wide gangways), to guarantee the best and safest travel conditions for the passenger. Passenger seats, individual or twins, are placed face-toface with a pitch of 1600 mm or in sequence disposition.

The design, the interiors and the painting are based on the TFA experience regarding similar trains recently projected and realized.

The traction equipment includes two 4-strokes Diesel motors, inter-cooled, with direct injection Common Rail, connected to a turbo gear with 4 gear ratios and power transmission to the shaft bridge by means of a cardan shaft. The turbotransmission is managed with an electronic system. The traction equipment is symmetrically placed on both the M1 and M2 motor coaches. Each motor coach is equipped with a “Traction Power Pack”, mounted under the car body frame, including the Diesel motor, the gear, the cooling system and other auxiliary equipments. All the equipments of the “Power Pack” are located into a box directly connected to the body structure. The “Power Pack” drives, through a mechanic transmission with gearbox and cardan shafts, each axle of the adjacent motor bogie. The auxiliary loads of the UD6 Traction Unit are fed by the hydraulic system.

The bogies are equipped with pneumatic self-levelling secondary suspension, braking disc system on each axle. The Hydraulic braking system, integrated into the turbotransmission, operates only on the motor axles. Full Adhesion bogies allow the train to take full advantage of the adhesion on steep gradients of route in all weather conditions.

Two air conditioning units for each coach of the train set, each with a double condensing section and double air treatment unit, guarantee an acceptable level of comfort in each passenger compartment even in case of single failure.