Elliptical bicycle sprocket. Drawing, description

PERSONAL TRANSPORT: GROUND, WATER, AIR
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Elliptical bicycle sprocket. Personal transport

Personal transport: land, water, air

Directory / Personal transport: land, water, air

The bicycle is perhaps the most common means of transport. And there is no doubt that it is the most economical: two sandwiches with butter are enough to pedal for two hours. But is it possible to increase the efficiency of the human "engine"? With a decrease in the cost of "fuel" nothing will work. Friction and machine weight are reduced to almost a minimum. There is also a "gearbox" device for changing the gear ratio by transferring the chain to small or large sprockets. It remains only to lengthen the levers of the pedals, but experts categorically state that their optimal length is 170 mm.

An original solution was the elliptical drive sprocket proposed in recent years. Readers are familiar with this invention in detail. With the help of an ellipse, the gear ratio changes cyclically, better adjusting the pedal mechanism to a person, but ... without facilitating work.

In the device offered to the attention of readers (Fig. 1), it was possible to synthesize the advantages of an elliptical sprocket and "long" levers: here the torque increases when, under pressure, unusual levers seem to lengthen, describing at the same time an elliptical curve, although the leading sprocket maintains the correct circle. This is how the gain in strength is achieved and the uneven change in the gear ratio is eliminated; the legs describe a circle with an optimal radius of 170 mm.

Rice. 1. Here is what the new pedal mechanism looks like (click to enlarge): 1 - bicycle frame, 2 - front wheel, 3 drive sprocket, 4 - pedal additional lever, 5 - lever sprocket, 6 - additional chain gears, 7 - connecting rod, 8 - bracket

Устройство

The pedal mechanism (Fig. 2) did not do without the usual main lever here - the connecting rod 4, on the hub of which an auxiliary sprocket 9 is put on. It is fixed relative to the bicycle frame - through the bracket 11. An auxiliary extension lever 12 is attached to the free end of the connecting rod on the hinge pedal 13. On the shaft of the lever 12, the second auxiliary sprocket 14 is fixedly fixed. Both gears have the same number of teeth and are interconnected by a chain.

Operating principle

Rice. 2. The main components of the modernized bike drive (click to enlarge): 1 - mounting plate of the drive sprocket, 2 - bracket, 3 - key, 4 - main lever (rod), 5 - stud, 6 - bushing, 7 - roller, 8 - bushing bearing, 9, 14 - auxiliary sprockets, 10 - support, 11 - brackets. 12 - extension arm, 13 - pedal. 15 - bearing ball, 16 - bolt, 17 - auxiliary sprocket bushing, 18 - washer. 19 - axis of the extension arm

When the pedal 13 is depressed, the main arm begins to rotate, while the sprocket 9 (through the chain and the second auxiliary sprocket 14) keeps the extension arm 12 always directed forward and horizontal. In this case, the general trajectory of movement of the extension lever is an ellipse, in the "front" half of which the largest radius falls on the pedal, and in the rear - on the hinge of the lever. Thanks to this, the forward pedal allows you to press it with maximum force precisely on the most productive section of the path - from top dead center to bottom, that is, when the main lever seems to be lengthening, which provides a gain in strength. Although in fact, when pedaling, they describe the correct circle with a radius equal to the length of the connecting rod (the optimal length is 170 mm), but extended forward by the length of the auxiliary lever (Fig. 3).

Production

For simplicity, let's consider the details one by one in order, as they are indicated in Figure 2. Plank 1 is made of pickled steel 5 mm thick. The connecting rod drive sprocket is bolted to it. Depending on its diameter and the shape of the middle part, the dimensions of the bearing part of the bar are selected (not shown in the drawing). Bracket 2. Two such brackets are made of pickled steel 3 mm thick. With them, the carrier bar is fixedly attached to the hub of the right main arm - with M6 X 8 screws with a countersunk head. Key 3. You will need two, made of St45 steel; their dimensions are determined by the cutout in the axis of the connecting rods and the size of the keyway of the hub. Main lever 4. Two of them - right and left, are made of St40X steel. They are connected to their levers (4) by welding. The keyway in the bushings must be on the same side of the lever. The hole for the pin (5) in the latter is drilled through the sleeve after welding. Hairpin 5 - from spring steel 65G without additional heat treatment. Sleeve 6. There are two of them - right (for the right lever) and left (for the left). Material - StZ steel. Roller 7. Rollers d 2,4x10,5 mm from the old crosspiece of the VAZ-2101 car were used.

Bearing sleeve 8. You will need two of St40X steel. Four holes d 5 mm are drilled in them simultaneously with the holes on the auxiliary sprocket 9 and bracket 11 Auxiliary sprockets 9 and 14.

There are four in total. They are standard, from the booms of the rear wheel, have 19 teeth (sold in bicycle parts stores). On two sprockets (9), holes are bored to d 39 mm. They can also be made as one piece together with the bearing sleeve 8 and the bearing sleeve 17. In this case, the number of teeth should not be less than 13. The main (without teeth) diameter of such an sprocket is 52,5 mm, and the outer one is 60,5 mm.

Support 10. Attached with two M3 screws to the left bracket 11 to provide sufficient front play between the bearing bush and the left main arm hub.

Bracket 11. With their help, the auxiliary sprockets are fixed relative to the bicycle frame. They consist of three parts: a shoulder and two brackets, bent in accordance with the diameter of the frame. The material of both brackets and four brackets is pickled steel 3 mm thick. The brackets are fastened with M5 screws, and after their bend along the frame is specified, they are welded.

Extension lever 12. There are two of them: both are made of St40X steel. At one end of each there is a hole for a pedal with an M14 thread, which should be of the same name: the right one has the right one, the left one has the left one. At the other end there is a hole for the axle (19); she is brewing. For greater strength, one or two blind holes d 4,9X9 mm can be made along the dividing line of the axis and the lever: before welding, stumps of a steel rod d 5 mm are driven into them, acting as a key.

Ball 15. In total, 84 pieces d 3 or d 3,2 mm are required for the extension arm bearings.

Bolt 16. There are two of them, M6X X 10 mm in size - for fixing the sprocket on the lever.

Bushing 17 for the auxiliary sprocket - two pieces - made of St40X steel. Three grooves along the periphery are machined under the protruding parts of the sprocket 14.

Washer 18. Two, made of pickled steel 2 mm thick; inner and outer diameters, respectively, 6,5 mm and 38 mm.

Additional recommendations

To manufacture the device according to these drawings, it is necessary to have a hollow axis of the carriage. An axle with square-tapered edges can also be used, but the holes in the crank hub must correspond to its dimensions, and the gap between the bicycle carriage hub and the crank hubs must be at least 1 mm.

The play necessary for the normal rotation of the extension arm relative to the connecting rod is achieved by selecting the thickness of the steel washer (washers) fixed between the axis of the extension arm 12 and the washer 18.

Elliptical bicycle sprocket
Rice. 3. Scheme of movement of the upgraded connecting rod: A - main lever, B - extension lever

The center distance at the main and auxiliary levers is approximately 172 mm. So that the chain does not have a weak tension, its size is determined during installation. How does this happen? An extension lever and an asterisk are mounted on the free end of the connecting rod. Another auxiliary sprocket and bearing sleeve 8 on the hub are mounted (not completely) on the axle of the carriage. A chain 590 mm long is put on both sprockets, stretched, after which the lever and the hub are welded to each other. When dismantling, the pin 5 is removed, a screw is screwed into the hole Mb, and the main lever (rod) is knocked out with a suitable bead through the hole in the central axis.

A trial assembly is made, before which parts 1, 2, 4, 8, 11, 12 and 17 are heat treated (cemented). Between the connecting rod and the extension arm, as well as between the main arm and the bearing sleeve, plastic seals are inserted, made from a 1 mm thick ring suitable for the diameter.

The pedal mechanism with automatic lever extension is recognized as an invention and is protected in Bulgaria by a copyright certificate. All those who have tried the novelty note not only the constructive originality of the solution of the task, but also the positive effect achieved due to it: the “acceleration” of the bicycle machine equipped with such a mechanism, easier passage of difficult routes and overcoming the rise.

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Comments on the article:

Moybike
It's great if you know how to do it yourself, and so - just order. Which certainly will not be cheaper than buying a ready-made sprocket for a bicycle.

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