Designing and accomplishing an electric shopping
cart and scooter trailer
eSCART
Designing and accomplishing an electric shopping cart and scooter trailer.
There have been existing separately electric scooters, hand-carts, bicycle trailers, goods-scooters. However, it is common experience that these functions are required jointly in the everyday practice. I combined these means of communication both in theory and practice. This vehicle’s wheels are similar to those of the scooters, its motor is similar to that of the electric scooter, and its tow bar is similar to that of the bicycle trailer. I retained the advantage of each appliance, and by means of a handlebar with two positions and an electric control further advantageous properties were featured for my vehicle beside the original ones.
- As an electric scooter, in downtown conditions; commuting between districts, villages, access to the school, workplace, maybe combined with public transport vehicles;
- As a trolley scooter, beside the approximately 80 kg average weight of an adult it can bear a further load up to 40 kg; its box for luggage enables transporting packets of greater volume as well;
- When the motor coasts you can use the appliance in a traditional manner; it is an archaic, nevertheless novel toy for children.
- It is suitable to transport luggage as a bicycle trailer, which provides 50 N rated thrust. On an ascent it can assist to struggle up; it facilitates the conveyance of heavier burdens. In its trailer function this is especially useful on a longer distance or in a hilly area.
- As a hand-cart, buggage trolley, electric push-cart, shopping cart, the shopping at the weekend can be managed without a car, as without a passenger it can carry even 100 kg. This weight burdens the three wheels evenly, and you may concentrate on the speed and the handlebar.
- I found such a function of which nobody has thought: placing my hand onto the reversed handlebar, walking beside the appliance, the cart can be driven easily either in motor driven or in coasting mode of operation. It is rated a hand-cart in this way as well but you can travel with it in a narrower place, and there is no need to turn forward the handlebar into hand-cart position. Likewise, when the handlebar is in the rear position, the appliance can be directed backwards conveniently.
- The dog carrying cart, electric golf-cart, hand-cart for news-boys and news-girls, using it in storehouses, warehouses are further possible variations.
- By means of a back-up switch it can go backwards with heavier burdens as well.
- In hand-cart position gripping the “accelerator handle”, when the vehicle lags behind, it can be accelerated immediately without varying the position of the hand.
- It can be transported without a bicycle-ticket by local and national railway, underground, and on escalators.
- By the eSCART it is easy to scooter up on the ramps enabling the access for the handicapped people.
- It can travel on the pavement, bicycle path; as a trailer and hand-cart anywhere on the edge of the road, in a one-way street even against the traffic.
- In shopping centres it can communicate from the bicycle parking to the counters and cash-desks.
- With the help of its big battery a mobile phone can be charged.
- Motor: 280 W (100 W in economy mode of operation, it can be operated in both directions).
- Sealed lead batteries: 2 pcs 12 V, 18 Ah (it stores approx. 0.36 kWh ≈ 8 HUF ≈ 4 cents with a single charging).
- Automatic battery re-charging on the slope.
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- Charging time: approx. 3 hours (for example at the workplace, in the school, university, at home, in the garage).
- Range: 20 km as a scooter (10 km/h) and 32 km as an active trailer (10 km/h original bicycle speed + 6 km/h owing to the thrust).
- It can be controlled also from the bicycle by means of an approx. 1.2 m long cable and a remote controller mounted onto the bicycle handlebar.
- XYK2000 24 V controller, which contains also the major part of the electronic circuitry.
- Digital voltmeter, which informs the driver continuously on the charging state of the battery.
- Load capacity: 20–40 kg as a scooter, 60–80 kg as a bicycle trailer.
- Aggregated weight of the motor and the batteries: 14 kg. They are located at the bottom of the box because of the centre of mass. A person of 80 kg average weight and high centre of mass had to be taken into account at the back, above the shafts.
- Thrust: 50 N in the case of 150 W, during approx. two hours, and 20 N in economy mode of operation.
1. Fundamental components
- Tow bar with cup-and-ball joint; when turned it becomes the handlebar.
- Strong mesh pocket located on the handlebar near the manual control.
- The boot for the luggage is a 60-litre plastic box with a mesh; when used not as a scooter, the vehicle can be loaded with 2-3 times greater burden.
- One or two driven wheels at the rear (diameter: 20 cm or 30 cm depending on the characteristic use), and a steered wheel in the front (diameter: 20 cm).
- Mudguards.
- Burden fastening rubber hook bands, and a strong mesh.
- Light reflecting strips, prisms in front, rear and at sides, bicycle lamp, removable, red flashing light and reflectors to the rear of the cart because in this manner it can be noticed in darkness, for example in bicycle trailer mode of operation.
- A battery charger providing standard 8 V voltage for mobile phone is also built in. In this manner, the phone can be used when scootering, shopping, hiking or camping if its battery is run-down.
- Bicycle lock, with which the device can be tied down in itself or together with the bicycle. The lock can be fastened by looping twice around the frame. It is safe enough because it is impossible to lose it during the ride, and practical because when the frame of the trailer is locked to the rear wheel of the bicycle there is no chance to remove the two vehicles together.
2. Accessories
- Speedometer.
- Safety lattice in the case of carrying dogs.
- GPS in the case of longer tour. It is useful to determine the location and besides, it measures the time and also the speed, and can be charged from the battery.
- Differential gear between the two rear wheels, which enhances the running stability when turning.
3. Implementation
Innovation: The bent handlebar tube was represented first with fractional lines. After manual designing I calculated the ideal angle between the two fractional lines, between the handlebar tube and the framework, then between the framework and the box, by means of a computer. According to the calculations it was found that the optimal handlebar position was when the incurvation of the tow bar was 106°, and the handlebar tilt angle to the framework was 20°. To this I had to examine three basic situations:
1. Scooter: all three wheels stand on the ground. The handlebar faces backwards. The electric regulator is operated with the right hand. The brake and the bicycle bell can be operated with the left hand. When braking the motor current is broken automatically.
2. Handle-cart: also all three wheels stand on the ground. The handlebar faces forward. The driver holds the tow bar by the governing arm (no need to pull). If he starts, the eSCART follows it automatically; if he stops, the cart slows down and stops.
3. Bicycle trailer: the device rests upon the two rear wheels, the tow bar is fastened to the bicycle frame with the cup-and-ball joint at 80 cm height above the ground level. The handlebar arches over the rear wheel of the bicycle, it must not hit the luggage rack either. The front wheel is at 8 cm above the ground. This prevents it from coming into collision with the road unevenness at higher speed. As the tow bar is fixed in this situation, the trailer safely pushes the bicycle with the transmission of the cup-and-ball joint.
Technical parameters measured actually by means of the GPS on 30th April:
I travelled 31.4 km by the eSCART with a single charging. The voltage decreased from 26.2 V to 23.6 V. During the travel the current intensity was 5–7 A. Accordingly, its consumed power remained below 200 W (120–150 W) during the 2 hours running. In the scooter mode of operation this power was enough to run at 8–12 km/h speed, and in the trailer mode of operation to push the bicycle with 14–18 km/h speed. The maximum speed was 23 km/h. The recharging started above 19 km/h. The own battery charger of the eSCART charged the batteries with 29 V voltage and 4 A current in 3 hours from 24.3 V to 28.1 V.
When the vehicle operates as a scooter, the control bar should be located at 105 cm height and at 55 cm distance from the vertical body plane. When it operates as a hand-cart, the control bar should be placed at 76 cm height for convenient gripping. At the brake and the handle the wrist angles were also taken into consideration.
The dynamic load of the frame structure was examined by means of the Cosmos program. The wiring of the XYK 2000 control electronics was snaffled from a mailing list on the Internet. To compile the pictures and films I applied digital editor programs. The technical drawings were prepared with CAD programs. The animated pictures placed onto the home page were created by means of gif-animator.
Simplified circuit diagram of the control device
The control device of the trailer can be mounted on the bicycle handlebar as well using a six-core cable, therefore 18 solderings were required than planned.
This vehicle can reach many places more easily than a car. For example, in the case of communication in the downtown, everyday commuting, shopping, etc. The device does not exhaust smoke and is nearly noiseless. In a hilly area you ride a bicycle provided with such a thrust with pleasure, in this manner you pollute the environment less as though you took the bike to the site by car.
The fossil energy consumption of an automobile is approximately 100 000 W, its self-weight is 1000 kg, the transportable burden is 200–300 kg and 1–4 persons but in the most cases merely 1. The correspondent parameters of the eSCART are as follows: 100–180 W, with 25 kg self-weight the transportable useful burden is 40–60 kg plus one person. In comparison with an automobile the energy efficiency of the eSCART is at least 100 times but less than 1000 times better. In the case of going to work and shopping day by day its energy consumption is daily 1 MJ (approx. 4 cents). This 1 MJ corresponds to approx. 0,025 kg (≈ 1 ounce) either fossil or renewable energy carrier.
Riding the scooter on the edge of the road you can step down safely from the vehicle and continue your travel as a hand-cart. It is illuminated in the appropriate manner.
As an automotive hand-cart the appliance helps the elder people to whom the communication is difficult to take home the goods from the shop. As a trailer it can be connected to a tricycle or wheel-chair. Nowadays when shopping centres have wheelchair access using the eSCART in more comfortable there too.
The functional forms had to be preserved. The arched tow bar and the profiles of the rectangular box are connected by means of a tilted tube framework, which plays a useful role to secure the rubber hook bands. The attractive logo is shaped from light reflecting foil, which ensures good visibility from the aspect of road safety as well.
When
fabricating the prototype nearly every component had to be purchased in
duplicate, so it can be stated that the cost of the trial series was 100
thousand HUF. On the basis of bicycle manufacturing experiences in the case of
100-piece series the price may be reduced to 70%. The motor block can be made
from the same plastic as the entire shopping box. The framework can be shaped
from ø16 mm steel tube as well, which makes the whole appliance lighter
and cheaper. In the case of 1000-piece series the electronic control unit can
be encased into a single water-proof block. In this way the planned 50 thousand
HUF guiding price in the Hungarian market, and the 195 € “greatly reduced
price” in the European markets are achievable. Considerable demand for the eSCART is predicted mainly in
What is missing
from the film of Robert Zemeckis …
We are in 2015:
A student is scootering blithely, with her bag at her
legs … and as if she was not pushing herself. A lady is coming out from the
shopping centre, and as if she were pushed by her shopping cart. A cyclist
locks his bicycle, disconnects the trailer with a single movement, reverses its
handlebar, steps upon the appliance and skims off. Silently and in an energy
saving manner as it befits the transport vehicles of the future.
I would
like to express my thanks to ones who helped me to implement my work submitted
to the competition, especially to my tutors: Venczel BORBÉLY (physics teacher,
Zsófia DŐRY