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PERSONAL TRANSPORT: GROUND, WATER, AIR
Amphibious all-terrain vehicle. Personal transport
Directory / Personal transport: land, water, air The off-road amphibious all-terrain vehicle on low-pressure tires, built by students and employees of the Technological and Economic Faculty of the Vyatka State Pedagogical University, has been in operation for more than ten years. During this time, the unique capabilities of the machine were confirmed. The all-terrain vehicle moves confidently on any road, on impassable dirty, snowy or swampy off-road, on terrain covered with bumps and bushes, overcomes water obstacles. With its own weight of about 250 kg, it is capable of transporting up to 500 kg of cargo by water and land. The all-terrain vehicle is made according to the wheel scheme 4x4. All its wheels are made steerable, which made it possible to reduce the turning radius to 6 m (with a smaller angle of rotation of the wheels). In front of the body there is a transparent shield (organic glass in a welded frame made of steel angle), which protects the driver from wind and rain, and also prevents the cabin from flooding with water when driving down a steep bank into the river. For the same purpose, the bow of the hull is strongly extended forward and is equipped with sealed cavities under the wings. Behind the open cabin (the driver's seat and the steering wheel in it are slightly shifted to the left of the longitudinal axis of symmetry of the body), there is a cargo compartment, in which, however, a passenger is also freely accommodated. To protect the driver and passenger from bad weather, a folding awning can be installed. The power unit is located in the stern, and above it is a roomy trunk welded from a steel bar with a diameter of 8 mm (it is also possible to replace it with a removable car). In the design of the amphibian, the power unit of the FDD motorized stroller is entirely used - the engine, gearbox, main gear, wheel hubs, brakes (virtually unchanged). Another main gear has been added to drive the front wheels. The frame of the all-terrain vehicle is welded. It consists of two spars, beams of the front and rear axles, curved trunnions with bushings for fastening the steering knuckles of the wheels, power unit supports and paired brackets for fastening the steering mechanism and the front final drive.
The frame performs mainly a layout function; the rigidity and strength of the entire structure of the all-terrain vehicle is given by its body, connected to the frame with four M10 bolts, although it does not have a power set. Its panels are cut from 8-10mm thick plywood and joined with 4x25 screws and epoxy. Then the butt edges of the panels were drilled in increments of 20 mm in order for the glue to penetrate into the holes and harden there like nails, and covered on both sides with 2-3 layers of fiberglass tapes on epoxy resin. After that, the body was completely covered with two layers of fiberglass on the "epoxy". Pigment and aluminum powder are added to the last layer of resin. Interestingly, in our opinion, the problem of sealing the hull at the exit points of the bridges has been solved. The openings in the housing are contoured with aluminum angle rings with rubber gaskets. Wide stockings made of rubberized fabric are attached to these rings by means of the same rings of a slightly larger diameter and M5 screws. The other end of the stockings is attached to the brake shields of the wheels with clamps made of profiled steel tape. Stockings are made with a margin in length so that the wheels can turn within the required limits. Thus, the entire transmission, power unit and other systems were well isolated from water, dust and dirt, which significantly increased their service life and reliability. The displacement of the hull has also noticeably increased - this is important for an amphibian. The control system of the all-terrain vehicle uses a steering mechanism, a steering wheel and a shaft with accelerator and clutch levers from the FDD (manual control of such a machine seems to us more convenient). The steering gearbox, steering linkage rods and steering knuckles of the wheels are of our own design. Each steering knuckle is cut from a 10mm thick stem plate. Holes are drilled in the workpiece for the wheel hub and its fastening bolts. Later, coaxial bushings and a lever with a hole for the ball pin were welded to it. With the help of these bushings and the king pin, the steering knuckle is pivotally attached to the frame trunnion. With this design, the maximum rotation of the wheel leads to some change (within 10 mm) of the distance between the ends of the axle shaft and the final drive shaft, which is quite acceptable and is compensated by the standard drive splined clutch. By the way, four hubs of the drive (rear) wheels of the FDD are used on the all-terrain vehicle. Steering trapezoid rods - from a steel pipe with a diameter of 25 mm, at the ends of which tips with lock nuts are screwed in, which allows you to adjust the angles of convergence of the wheels. The thrust of the front steering trapezoid is set in motion through an earring welded to it and a ball pin directly from the gear rack of the steering mechanism. To control the rear wheels, the front and rear steering linkages are connected by a transmission shaft with levers at the ends. The shaft rotates in the sliding bearings fixed on the right side member of the frame. The levers through the bushings are pivotally connected to the pins welded to the steering rods. This ensures the synchronous rotation of the front and rear wheels in different directions. The above construction seems to us to be simpler and more compact than the system of levers, pendulum supports and rods used in such cases. The layout of the all-terrain vehicle is such that the axes of the steering shaft and steering gear were at an angle of 60 °. Therefore, it was necessary to make a gearbox with two bevel gears placed in an aluminum alloy housing. The gearbox is attached to the body of the all-terrain vehicle with two brackets made of steel sheet 3 mm thick. To reduce the rotational speed of large diameter wheels and increase the torque, the power unit is equipped with an intermediate shaft that provides a gear ratio of about two. A slightly modified intermediate shaft from some kind of walk-behind tractor with one sprocket z = 21 and two - z = 11 was used. The tubular shaft rotates freely in needle bearings on an axle that is fixedly installed in the holes of the cheeks drawn to the frame of the power unit at the attachment points of the main gear . The intermediate shaft is driven by a chain from the drive sprocket of the secondary shaft of the gearbox. Also, the intermediate shaft is connected by chains to the sprockets of the input shafts of the front and rear final drives (the input shafts were turned upside down before that, which was easy to do because of their symmetry). The distance between the axes of the intermediate and primary shafts of the front final drive is about 900 mm. Chain tension is required to prevent slack and contact with the body. The tension is carried out by deflecting the power unit on an elastic suspension using a sliding rod (not shown in the drawings). During the operation of the all-terrain vehicle, it turned out that the regular rubber-metal couplings of the FDD half-axes are not strong enough and quickly fail. In addition, their elasticity significantly increased the effort on the steering wheel needed to control the car. Therefore, they were replaced by cardan joints (crosses) from a UAZ car. The axle shafts and splined couplings are from the FDD, their ends are cut off, and the universal joint forks are welded to them. The design of the transmission allows you to turn on the front and rear axles separately. Experience has shown that the need for their simultaneous operation is quite rare: as a rule, in particularly difficult areas - when leaving the water on the shore, driving over high bumps, and so on. However, it is precisely in such modes that a rapid accumulation of the difference between the front and rear wheels is possible due to the difference in their sizes, air pressure, uneven rotation on an uneven surface, which leads to the appearance of excessive stresses in the transmission due to "power circulation". This is fraught with breaking chains, breaking gears in gearboxes and even destroying their cases (all this happened to us). To prevent these phenomena, the mechanism for engaging the forward gear of the main gear of the rear axle has been finalized. The back, non-working parts of the cams of the forward gear and the cam clutch, which engage with each other, were removed on emery at an angle of 45 °. Thus, in the event of a reverse torque on the wheels, the gearbox is now either automatically placed in a neutral position, or it turns into a freewheel. It is known how much the differential lock increases the vehicle's patency in difficult conditions. In our case, this is especially important when leaving the water on the shore and driving through the snow. However, it is not possible to ensure the blocking of the standard differential of the main transmission of the FDD without major alterations. An easier way is to turn the differential into a freewheel. To do this, seven out of ten teeth at each satellite were ground off on emery; the cavity between two of the remaining three is filled with molten metal by electric welding; and the satellites are spring-loaded on the finger, turning into ratchet pawls, each for its side gear. Thus, free rotation of the side gears is provided faster than the differential box (cups) (when, for example, the outer wheel enters a turn), synchronous rotation of the wheels and high off-road capability when driving in a straight line and when slipping. And in the end - satisfactory handling of the all-terrain vehicle. The disadvantage of this method of "blocking" is the impossibility of using the front axle in reverse (we have removed the reverse gear from the front final drive), but there are still more advantages. An important part of such machines is wheels and tires, because they provide their increased cross-country ability. The lack of suitable industrial-made wheels forces amateur designers to find their own ways. Our rims are aluminum cans with a diameter of 450 mm. I must say that they are made of a rather thick sheet (2 mm). Now thinner ones (1 mm) are more common on sale, they are suitable only for use for their intended purpose. The disks are fastened between each other and with internal plan washers made of duralumin sheet 5 mm thick with five M8 screws; they are attracted to the FDD hubs by four elongated nuts.
The strength of such discs is quite sufficient for the operation of an all-terrain vehicle in normal conditions. However, when driving carelessly over stumps, high bumps and fallen trees, when overcoming deep ditches with acceleration, and so on, such discs are sometimes crushed, usually from the outside. Therefore, we reinforced them with 100 mm thick foam inserts. The liners are tightly pressed to the discs with external plan washers 3 mm thick and nuts screwed onto studs that are inserted into the elongated wheel nuts. In addition, the foam increases the buoyancy and stability of the all-terrain vehicle on the water. Tires of low pressure - double chambers 900x300 mm in size, which have served their resource in aircraft wheels. The outer chamber is cut along the inner diameter and attached to the disk with M8 screws with spherical heads. For better grip with the ground, as well as to limit the dimensions, a perforated conveyor belt is glued to the outer chamber. The wide track and short base of the all-terrain vehicle chassis, low pressure in wide thick tires (0,2 * 105 Pa) make it possible to do without a suspension at all, which greatly simplifies and facilitates the design of the machine. The only inconvenience associated with the lack of suspension and found by us during operation is the longitudinal buildup (resonance) of a loaded all-terrain vehicle at a speed of about 20 km / h. We got rid of this by supplying the trunk with shock absorbers from a scooter. For several years, the all-terrain vehicle was operated without a propeller, moving through the water due to the rotation of the wheels. However, the speed of such movement was very low, especially with a headwind and waves. The blades mounted on the side surface of the wheels did not help either. Currently, the all-terrain vehicle has a propeller from the outboard motor "Whirlwind-20", which is driven by a chain from the engine fan shaft through a modified gearbox from the same "Whirlwind". The refinement consisted in the manufacture of a new housing and mounting bracket, lengthening the driven shaft, installing a bushing with an asterisk on the drive shaft-gear. The new gearbox housing is welded from sections of steel pipes of suitable diameters, machined to fit the standard gearbox parts. Particular care was required to weld the parts of the hull together and with the mounting bracket to prevent warping. The driven shaft is extended by 250 mm using a nozzle made according to the dimensions of the standard shaft and connected to it with two steel rivets. The elongation required the installation of an additional support - the ball bearing 204 is fixed in the housing with a threaded cover with a lip seal. The torque from the engine to the drive shaft of the gearbox is transmitted through a bushing with a square hole, made according to the dimensions of the standard gear shaft. The connection between the sprocket and the bushing is welded. A ball bearing 204 is fixed on the sleeve with a nut. The clearances in the gear train and the drive shaft are fixed in the housing are carried out by the same threaded cap with a lip seal (there are holes in the sprocket for screwing it in). The driver controls the gearbox from his seat using a lever having fixed positions "forward", "neutral" and "back", and cable wiring (not shown in the drawings). The speed of movement on water is 5 km / h, which is quite enough to overcome water barriers even during spring floods. When moving on land, the propeller and chain drive can be easily dismantled. Due to the installation of the propeller gearbox, the use of a standard muffler for the FDD motorized carriage became difficult. I had to make a muffler from pipe sections of various diameters. The body of a pipe with a diameter of 80 mm is welded at the ends, the inlet and outlet pipes inside have 12 holes with a diameter of 8 mm. No reduction in engine power was noticed, the noise level increased slightly compared to the original. Author: V.Multanovsky, G.Semenovykh
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