The story of another electric bikes do-it-yourself v2.0

Foreword

In the last article, I talked about how I built an electric bike from components for radio-controlled models and materials at hand found in stores. At the end of the article, I mentioned that I was going to remake the V-belt transmission on the gear. I submit a report on what came of it.

(There are pictures and video)

As I mentioned in the last article, the main disadvantage of the V-belt transmission is its low efficiency compared with a gear and low gear ratio, since The V-belt is rather thick and it bends poorly, and therefore the radius of the small pulley cannot be made sufficiently small in relation to the large pulley. On the pulleys applied by me in the last construction from the generator VAZ-2108, the gear ratio was 2 (2.34 when using the pulley from the washing machine).

So I decided to order the sdp-si gear pulleys for the belt and the belt itself. To do this, use their calculator . The calculator is quite convenient - it allows you to select the number of teeth on the pulleys depending on the desired gear ratio and the distance between the centers of the pulleys, as well as a suitable belt. I asked the largest possible value of the gear ratio and limited to plastic pulleys, because metal is too expensive. The calculator offered me the following option:
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A 6Z 3M15DF09508 - plastic pulley for 15 teeth with two sides and an aluminum insert (for mounting on the engine), price $ 6.91 ( datashit )
A 6L 3M78SF09510 - plastic pulley for 78 teeth with one side without insert, price $ 11.50 ( datashit )
A 6R 3M116095 - neoprene strap size 5.08mm (XL) for 116 teeth 9.5mm wide, price $ 7.53

Delivery costs $ 7 + overhead $ 3. Total cost $ 37.

After a month of waiting and receiving the parcel, I got to work.

Manufacturing

In the new version of the electric bike, I decided to move the entire power structure to the rear trunk so that it does not interfere under my feet. As last time, an aluminum profile was used to fasten the elements.



Since the large 78-tooth pulley had a wide seat and when installing it on the adapter sleeve there was not enough space for the nut, I had to grind off one side of the seat flush with the plane of the pulley (seen in the photo). For this, I used a manual boron machine with a nozzle in the form of a metal disk (other nozzles turned out to be fragile and broke).



Small pulley stood as expected, because in the final selection in the table on the sdp-si website, I immediately indicated the corresponding diameter of the motor rotor.

As a chain tensioner, I also used a speed switch, only now in a vertical position. Frivil also stayed.



I did not feel any special difficulties in placing the components. Rather, on the contrary, the layout on the rear trunk seemed to me more successful and convenient.

Tests

Difficulties arose after the first test run.

1) With a sharp increase in gas, the engine pulling force on the chain turned out to be so strong that the left support, made of an aluminum strip 2 cm wide, was bent under load. This led to a distortion of the whole structure and the slipping of the chain from the frivil. The solution is to replace the support with an aluminum profile 2x1cm. Profile does not bend :)

2) At high speeds due to the uneven tension of the chain (due to the curvature of some elements - the driven star, etc.), when the gas is released, the chain jumped from the frivil. A similar problem arose when moving over bumps. The solution is to install a chain stop (damper) from an aluminum strip just before the freeze. The disadvantage of this solution is that the chain beats on the limiter and sounds unpleasant.

3) The most important and not yet solved problem. Before buying pulleys and a belt, I read a few topics on the endless-sphere about such applications of a gear train and found out that basically two types of HTD and XL belts are used. HTDs are less robust than XL, but can be used at very high speeds. In my case, the maximum rotational speed of the engine was 10,000 rpm / min in the XL belt, so I opted for it. I also focused on the distance between the teeth and the XL type belt variant seemed to me optimal, because for him, this distance is 5.08 mm. The next larger version is only L (9.525mm). I felt that XL should be enough. However, after the opening of the parcel, the very small belt teeth alerted me. They turned out to be no more than 1.5mm wide, and the remaining 3.58mm is the empty space on the belt. The height of the teeth and even less. It was the small teeth that caused the problem, namely the belt slippage. Honestly, I could not even think that the toothed belt could slip :) Slipping occurs with a sharp increase in gas at low speeds. In such modes, the engine can produce up to 1.5 - 2 kW of power and such a belt is simply not able to transfer it to the wheel. A temporary solution to the problem was to limit engine power to 800 watts. It has become much easier to control the handle of the gas, there are fewer moments with a belt break in slipping. However, this limited the maximum speed to 25 km / h.

Results

The total gear ratio in this scheme turned out 78/15 * 52/16 = equal to 16.9 (compared to 11.4 for the previous version). Even with a limited power of 800 watts, this is enough to go up to the unloved hill on the way to work at a speed of 15 km / h :) The maximum speed is 25 km / h. A battery with a capacity of 5000 mAh (22 V) is enough for 12-14 km of journey (compared to 8-10 km in the previous version). On the face, an increase in efficiency of ~ 40%.

Additional materials (video)

Overview of the bike and the main components



Demonstration of acceleration at idle in the "full throttle" mode.