same time the vibrations that plague these mechanical systems.
In fact, any axis can not turn in a level if there was a small gap between the two diameters, a difference that one aims to minimize but never zero - if the That was the two pieces would be spinners, which is a good mounting system but no rotation.
There is no mechanical joint without a clearance between all moving parts but these are not geometrically perfect, and when they are rotated is the centrifugal force pulled them round the side where the unbalance. The axis starts to beat in the landing at the same rate as the rotation, vibration and shocks are a major cause of fatigue and wear of organs.
translational movements give rise to the same vibrations because the parts are never really straight in the mathematical sense of the word. It can bring great attention to balancing and machining of components, reduce vibrations and keep them within limits as they do not interfere too much, but we can not eliminate totally. The hunt for unbalance and misalignment is a priority in the engineering industry, but it can also original path, look for the imbalance to create the movement.
we build today. It is unique in that advance, then no force is transmitted to driving wheels, and he of course has no sails or propellers.
In fact, it is strictly a jet engine, but it was understood by Newton when he formulated the principle of action and reaction: there is neither nor rocket nozzles, but simply a lotte eccentric mass which causes a horizontal action and opposite reaction the direction of travel.
The craft could not be simpler: one mounted on a chassis with 4 idlers, an eccentric weight, a horizontal axis parallel to the axis of the wheels and driven by a motor. Any platform with 4 wheels is fine, but the weight must be proportionate to the mass of the platform and the speed of rotation is given to the characteristics of the inertial platform - mass moment of inertia , resistance to progress in one direction or another.
Hopefully, once we start the engine you see the frame vibrate, oscillate, then get moving. A priori, there is something quite contrary to the laws of physics: the imbalance causes many oscillations, but they are equal up and down, forward and backward.
So the car should start to rise when the weight is up (the centrifugal force pulls at that point upward, causing the axle housing and all), then move a little when, in its rotation, it passes front, when it comes crashing down and go back an equal amount in advance when she finds herself on the back. This oscillation
round is indeed what we observe in general: the frame is shaken from top to bottom and front to back around a mean position without really advancing one side or the other. But it also happens that the platform carrying the eccentric on the back starts to move forward - or back, which is the same: a car that never recedes a self advancing in the direction of the trunk .
In principle, no torque exerted on the wheels and the reactions due to the centrifugal force of the eccentric vanishing into a full turn, the chassis should not move forward. As it progresses anyway and that the principle of action and reaction formulated by Newton three centuries ago has never been reversed - any action opposed by a simultaneous reaction of opposite and same intensity - you must seek the explanation in the framework of classical mechanics.
Let the flow diagram: when the weight is forward, the centrifugal force that pulls the system in the direction of the unbalance thus causes the shaft forward, the latter being connected to the chassis is weloganite advance as it is linked to anyone. Of course, there is growing only a tiny distance: more than a few millimeters. In this progression, it must overcome the resistance force due to friction of the wheel shafts in their bearings, and friction of the tires on the ground. When the weight
has retaken the top-down, the centrifugal force pulls in the opposite direction and tends to reduce the mobile. If the frictional forces were fully equal in both directions, the setback distance would be equal to the distance of advance and the mobile would oscillate back and forth from the vertical.
In practice, just sheer luck that the resistance to motion are not equal in both directions: the tire's grooves are oriented, there is more oil on one side of the bearing that the other, that the unit is on a rug whose hairs are lying in a certain direction, and so on.
Ideally, the resistors in one direction and the other are never equal, but they can be very similar, especially with the path variable (very small) come: at this time the mobile moves up a fraction of a millimeter, then the meaning of reversing resistance because the wheel has met a nugget when the axis is a little hazy, it goes back an amount roughly equal, then leaves forward, then backward, and finally stood still.
By cons, if the weight is quite large relative to the chassis, front-back trips are large enough that their difference is still significant and finally moving forward in one direction. Failing that, and that's what we did, we can intervene so that the resistance to progress in one direction and both are very different: Simply put a ratchet wheel on the one axis. The gear can move forward but not backward.
This kind of wheel with bevelled teeth and a pawl spring is not very common Courbier Pierre, after modifying the model of our reader, greatly simplified device: a flexible blade used to catch, and a tire Fischer Technik sculptures to highly visible acts of wheel teeth oblique. Through this flick the fate of thumb, we avoid having to give precisely the unbalance mass to that of the complete equipment, and patiently seek the right to give the engine speed.
To be fair, the mobile can be constructed from any components: Meccano, Lego, Fischer Technik, or elements of any recovery, the whole is to have a platform on 3 or 4 free wheels, and set over an engine with a wheel offset - a weighted wheel will do. This is to say that everyone can build its own mobile, and that we propose is a model that countless personal variations.
As always our database construction is high impact polystyrene sheet 2 mm thick that can be purchased directly or through correspondence with Adam Montparnasse, 11 Boulevard Edgar Quinet, 75014 Paris, or in Pierron, Sarreguemines Cedex 57206.
Regarding the other elements, we said, we strive to make best use of what is available to hand axes, screws, pulleys, nuts can be found at the hardware store, to the specialist scale model ... or at the bottom of a drawer. To be honest, the truck could be inertial as well as Meccano, Fischer Technik or in Lego.
Our model, produced by the method Hobbystyrène Paul Courbier, uses polystyrene sheets of 2 mm. It starts with the frame by referring to Figures 1, 2 and 3. After drilling four holes of 4 mm on parts B and B1 to the dimensions shown in Figure 2, we assemble the parts A, B1, C, C1 to form the frame.
To obtain proper alignment of the bearings, it will be advantageous to drill the parts B and B1, overlapping and immobilizing them beforehand with tape. All wheels are fixed on their axes, they revolve freely in their bearings. One can, if desired, make two free wheels by cutting them into disks 47 mm polystyrene (technical Compass cutting).
For receiving the ratchet wheel, we took pieces Fischer Technik 47 mm in diameter, which contain a black plastic bandage whose drawings will play the role of ratchet teeth for this, we improved the adhesion of these wheels by providing them with a rubber band that snaps into the groove provided for this purpose. The axes were made of steel rods of 110 mm, the diameter of 4 mm.
block propulsion is illustrated Figures 4, 5 and Figure 6. It will trace, mark and cut off parts D, E1, E2, E3, E4, F, G, H, I1, J1 and J2 - Figures 4 and 5 - and they pierce a hole 4 mm. Because of the oscillations that may be incurred levels, each consisting of two pieces glued and stacked - respectively E1, E2 and E3, E4. Two squares J1 and J2 will keep them upright on D.
The weight is cut to the dimensions given in Figure 5, to increase its bearing on the shaft (steel or brass rod, 4 mm, 80 mm long), it will be strengthened to one of its ends by the two squares I1 and I2. This breakthrough will end, after drying, a 4 mm hole - providing drilling on all three parts stacked and assembled temporarily with tape. On either side
on the other end of the arm of the weight, it will stick (cyanoacrylate) three rectangles of lead thickness of 1.5 to 2 mm, two on one side and the other, if we do not have sheet lead, we can replace it with a twist or solder parts stacked and glued two francs, their number is fixed in later tests.
We stick on D, at the location indicated in Figure 4, a bearing supports with its square. Then stick midway between the ends of the axle weight (cyanoacrylate) and sheave (Pierce) 30 mm in diameter. The pulley is glued to both the axis and on the side of the weight, all of which form an integral assembly.
then cut the spacer spacer in a plastic pipe of 5 mm. Their length should be such that the weight is disposed at an equal distance from both ends of the axis. It will then install the parts by gluing on an interim basis D (by adhesive dots) is the second tier, not forgetting to put washers - Figure 6 - from both sides of the spacers and have the rubber band (diameter of 40 mm) which will serve as a drive belt.
It remains to develop the engine, we chose a motor Mabuchi BE 26. In fact any electric motor recovered from a toy (and 99 times out of 100 is a Mabuchi, wondering which manufactures engines from them) can agree - but often these motors have a shaft too short and should be extended by a brass tube glued end. We used a long tube of 3 cm (internal diameter 2 mm, 3 mm outside) that is bonded to the cyanoacrylate on the axis. This
paste operation is delicate and must be careful because the glue is very fluid and may seep into the bearing's internal engine, in this case, blocking is almost always irreversible and it only remains that to discard. Therefore it is advantageous to use cyanoacrylate adhesive gel-like and not put a tiny amount.
The engine will be powered by two 1.5V batteries (LR20 type) connected in series. As it is desirable to adjust the speed of rotation, we planned to insert into the circuit a rheostat (potentiometer wound of 15 ohms). This solution, lax technically as part of the battery power is unnecessarily converted into heat, but the advantage of simplicity of execution and allows fine tuning of the engine speed.
Note that a potentiometer has three terminals, in our case, we will use it as a rheostat and make the connection the central terminal and any of the other two. Mabuchi Motor has
output side of the axis of a shoulder diameter of 6 mm to be inserted and glued (cyanoacrylate) in a hole drilled in Room g, which will then be fixed (Uhu glue-Plast) at its location provided on D - Figure 6. A cutout is provided on this piece to allow the passage of the rotating feeder.
The second level of the motor shaft will be drilled in Room H - hole 3 mm in diameter. Before gluing h on D, we will set up the belt and that collages are dry, they will try the operation engine block after putting a drop of oil in four levels. The perspective view of Figure 6 specifies the provisions of these parts.
To hold the two stacks, we used two cases of type connectors Wonder Sollo, any other solution can be agreed, including the son of direct soldering to batteries - but in this case, a switch is necessary. Son of the welds connecting pose no difficulty. If the pot is the type with plastic housing and integrated axis, it will be necessary to secure the frame.
Ours, adjustable with a screwdriver, was directly welded by one of its terminals on the housing pods batteries. It remains to assemble the two units Sollo using the grooves provided for that purpose, and then paste them on the back of the frame using pieces of Scotch Mount.
The catch is shown in Figure 7, 8 and 9. In a rectangular strip (6 x 45 mm) brass with about 0.3 mm thick - a big blade battery 4.5 V should be fine - we will cut a notch as indicated in Figure 7. The end is not wound on notched itself with blunt nose pliers to form a cylinder marrying a 3 mm screws 18 mm long.
This screw will be inserted into a hole the same diameter drilled in Exhibit B (See odds Figure 8). We then arching the tongue immobilized by the nuts which enclose both sides so that its tip rests in the notched edges of the toothed wheel tire Fischer Technik.
To play its role properly catch the end of the tongue must prevent the return behind the wheel, but the friction in the other direction should be as low as possible. That is why fine tuning is necessary we will do with pliers flat moving the carriage by hand until the best result is achieved.
There will be no later than proceed to trial on a surface smooth and flat - for lack of flatness, the craft went down the slope but do not usually go back. The settings will be to turn the shaft of the rheostat to obtain the speed of rotation to advance the cart without it being subjected to too great upheavals. We will
managed to make a device that apparently progressing without support or force applied to the wheels. All the mystery lies in the principle of action and reaction, and the asymmetry between the forces of resistance to progress in one direction and in the other. But it is not clear to him who discovers for the first time this curious mobile.
0 comments:
Post a Comment