Analysis of Analysis of Naturalistic Electric Bike Rider Behavior: Energy and Power

Fishman, Piercy 1

Analysis of Analysis of Naturalistic Electric Bike Rider Behavior: Energy and Power Considerations

Noelani Fishman, West High School; Breanna Piercy, Hardin Valley Academy

Kwaku Boakye, Dr. Shashi Nambisan, Dr. Chris Cherry

Abstract

Electric bikes (e-bikes) were developed to provide hybrid human/electrical power to help propel riders. Studies determining how much power is exerted by riders of e-bikes are limited. This study attempts to quantify and compare the overall energy-use of riders of e-bikes and regular bicycles using fundamental physics relationship with real-world data. Data from naturalistic bicycling behaviors of two riders (one with e-bike and the other with regular bike) were obtained using GPS devices. Analysis of the data showed that the e-bike rider, on average, exerted about half the power used by the rider of the regular bike. This project compared the energy output of regular bikes versus electric bicycles.

1. INTRODUCTION

In foreign countries such as China or some parts of Europe, a need has arisen for a cheaper and more efficient mode of transportation that allows consumers to travel through city streets with ease. In the past, motorcycles and traditional bikes have curbed a large portion of this demand. In recent times, however, e-bikes have also begun to compete with regular bikes and motorcycles in foreign markets where the demand for this type of vehicle is high. This sudden boom in e-bike consumerism has led to a need for more and more innovative electric bikes. Research in how to create cheaper models, more efficient batteries, and other such improvements could allow e-bikes to become more widespread in the world market. This study is a step in this process of bringing e-bikes to a global stage. By defining the energy efficiency of e-bikes, this study has paved the way to future studies that can be done in this field. This will eventually bring the world to a more energy efficient transportation environment.

II. LITERATURE REVIEW

In 2012, the University of Tennessee hosted the United States’s first e-bike share program known as UT’s cycleUshare. It lasted for one year consisted of a fleet of 14 bikes split between two stations that could be found at separate locations on campus. One of these stations was completely solar powered. As it was a research project, the bikes could be accessed for up to 4 hours at a time for free. This was done in order to collect naturalistic data from the bikers. Unlike the more recent study that is explained in this paper, this previous project had a wider variety of bikers and bikes from which to gather data. Furthermore, the newer study takes the older one a step further by comparing e-bikes to traditional bikes.

In this study, an e-bike from UT’s cycleUshare program was used to collect the data. This type of bike is called a pedal assist bike. This is one of the four types of e-bikes available.There are four classes, listed here in order from Class 1 to Class 4: pedal assist, throttle on demand, speed pedelic, moped or motorcycle. A pedal assist e-bike has an electric drive system activated only through pedaling and can only has a limited amount of speed it can assist the rider with. A torque sensor on the bike measures pedal movement, pedal torque, or bike speed, sometimes a combination of two or three. The speed of the bike’s electric drive system is generally limited to twenty miles per hour in America, and around fifteen miles an hour in Europe.The electric drive system of a throttle on demand e-bike is activated by some type of throttle on the bike. The speed of this bike in America is limited to 20 miles per hour while in Europe it is limited to 15 miles per hours. A speed pedelic e-bike is similar to Class 2 e-bikes except that it reaches higher speeds. In America, this Class is often combined with the second class while in Europe is does not have the same rights as regular bikes and requires a license. In both America and Europe, it may be restricted to driving on roads and private property at no greater speed than 28 miles per hour. When an e-bike is considered a moped or a motorcycle, that means that it goes too fast and the motor wattage is too high for it to be considered a bike under the federal or state law. While all of these classes of e-bikes seem very different, there is one thing that they all have in common. Every e-bike has three main components: the battery, motor, and controller. The battery of an e-bicycle is usually a lead battery, often referred to as a Sealed Lead Acid (SLA) battery. Due to the battery’s bulkiness, weight, lifespan, and maintenance, companies are looking for alternative battery options. The newest technologies in store for the batteries used on e-bicycles are Ion, Polymer, Manganese, and others. These all have life spans that are two to three times one of a lead acid battery. In this study, a Lithium battery is used that has 240 watts of power.

The motor is also a very important component of an electric bicycle as it adds the most weight, ultimately slowing down the bike. Typically, the motor is from 200 W to 1000 W. The limit in the United States is 750 W, or it is considered a motorbike. The higher rating the motor is the more weight it can pull with greater ease but the faster it draining the battery. The most common type of motor for electric bikes is hub motors. Hub motors are generally incorporated into the wheels of the bike. This motor pulls or pushes the bike but at the expense that it loses efficiency on varied terrains.

Lastly, the controller is the final component that makes an electric bicycle an electric bicycle The two types of controllers are the pedal-activated controller and the throttle based controller. The pedal-activated controller allows the rider adjust the level of assistance which ranges from no assist to full assist. The second type of controller works with throttle mechanism, twisting or gripping. The modes of operation available to an e-bike are the pedal only, pedal assist, and electric only. Below is a graphic illustrating the locations of the aforementioned components on the e-bike used in this study.

III. METHODS

Throughout the process of discovering the energy exerted by both the regular bike rider and electrical bike rider, there were many steps and equations that were needed in order to properly analyze the data. For the first step in this project, research was done analyzing previous projects. This developed knowledge of e-bikes and why they were not widely used throughout the United States but were more frequently used as an alternate mode of transportation in places like China and the Netherlands. The research also provided knowledge concerning how an electric bicycle operates. The research was extensive, which ultimately assisted in the later parts of the project.

Since the goal of the project was to determine the energy exerted by an e-bike rider in comparison to a rider of a regular bike, it was decided that one subject would ride an electric bicycle with the assistance of the electric motor while the other would ride a traditional bike. The subjects then rode their designated bikes along the Greenways surrounding the UT campus. Different paths were travelled each day. Above is an example of one the routes travelled during the data collection process. Data were collected for 1-2 hours each on four days. Both bike riders rode brought handheld GPS devices that collected the naturalistic data. This means that the devices collected data that was derived from the riders while they were acting like they normally would. The GPS devices were linked with a software program called GoldenCheeta, a program that analyzes data from devices such as the ones that were used in this project. This program measure factors such as speed, cadence (revolutions per minute), altitude, longitude/latitude, the route which the subjects took, and other related subjects. Each day after a ride during the data collection period, the data from the devices was extracted and downloaded onto GoldenCheeta. After all the data had been collected, the raw data was transferred to Microsoft Office Excel where it was applied to the below equations in order to find the variable “W”, or power.

W=V[Kₐ(V+Vw)²+mg(S+Cr)] …..eq. 1

Cr=0.005{1+2.1/P[1+(V/29)²]} …...eq.

where W = Power, Kₐ = Aerodynamic drag factor (kg/m), V = Speed relative to ground (m/s), Vw = Headwind velocity (m/s), m = Rider + bicycle mass (kg), g = Acceleration due to gravity, S = Slope of hill ( % Grade) , Cr = Rolling resistance coefficient, P = tire pressure

The second equation’s purpose was to determine Cr since the rolling resistance coefficient was unknown. The rolling resistance equation took into consideration the tire pressure and other variables. With these equations, more raw data was determined. Below is a representation of some of that raw data.

In the raw data, the power exertion has already been calculated. After this step, the results from the data were organized into the table that can be seen below.

Electric Bicycle Data

Day / Total Power / Average Power / Total Cadence / Average Cadence
Day 1 / 86343.21 / 25.85 / 93639 / 23.04
Day 2 / 163982.89 / 44.65 / 73527 / 14.68
Day 3 / 123033.15 / 38.08 / 70130 / 16.03
Day 4 / 193112.30 / 35.99 / 120142 / 19.80

Regular Bicycle Data

Day / Total Power / Average Power / Total Cadence / Average Cadence
Day 1 / 88250.19 / 25.20 / 65237 / 16.08
Day 2 / 140632.76 / 32.38 / 29707 / 5.29
Day 3 / 146862.76 / 39.33 / 31166 / 7.11
Day 4 / 249191.93 / 44.27 / 65793 / 10.46

As demonstrated by the above data, the cadence and the power for the electrical bicycle are greater. This is because the electrical assistance provided by the e-bike motor made the bike easier to pedal. For example, if an e-biker and a regular biker go up a hill, then the e-biker would have an easier time pedaling and a higher cadence than a regular biker. Although these rates may be higher for the electrical bicycle rider, the regular bicycle rider had a higher ratio of power per cadence in comparison the e-bike rider. This means that the regular bike rider exerted more manual power than the e-bike rider, where the e-bike rider made up the power with the electrical assistance.

IV. RESULTS

Once the power exerted by each rider was divided by the cadence of each rider, the manual power exerted by each rider was determined. As shown in the graph below, the rider of the traditional bicycle had more manual power output than the rider of the electrical bicycle. The electrical bikerider yielded about half as much power per cadence than the regular bicycle rider.

Different types of variables could have affected the results. For example, weight of the rider and bicycle, exercise level of the rider, exhaustion, temperature, and other factors. Some of the main factors that affect the results of this study are the different types of resistance. There are three main types of resistance related to bicycle riding. The first type is aerodynamic resistance, and this is the amount of power it takes for the bike to push forward against the wind. Another type of resistance is Rolling resistance, otherwise known as friction. This is the amount of power the bicycle needs to actually move against the ground. Lastly, there is slope resistance, which is the resistance created by going uphill or on difficult terrain. All of these are factors that may have altered the results, and because this data is naturalistic, it is prone to variables such as these.

Also, there was analyzation of the correlation of data between speed, altitude, and cadence. The speed and cadence followed the same trend. This is because as one pedals more generally the faster they become. These numbers were farther apart for the electric bicycle. When the altitude was in a constant flat area, the cadence and speed increased. However, when altitude increased in hills or slopes, the speed and cadence increased for this as well.

V. DISCUSSION

The results resolve as was predicted in previous projects. The results quantify the amount that electric bicycles exert more power than a traditional bike. Other projects have been done centered around the fact that e-bike riders exert less manual power. However, no one has ever put it into numbers the amount of manual power the electrical bicycle rider actually puts into the ride compared to the manual power of a regular bicycle rider. They show that with electric bicycles one can travel faster and farther with more ease than a regular bicycle. The overall point of this project was to quantify how much less manual power electric bicycles use than traditional bicycles. This project completed the study previously completed by Professor Cherry. The research will be a gateway to other types of research.

The use of this project is to encourage the use of electrical bicycles. Hopefully, in the future, Americans will realize how energy efficient electrical bicycles are. With these results, there is no room for doubt that electric bicycles are easier for travelling use. Although some may still prefer traditional bicycles for recreational use and traveling longer distances, such as travelling to work or other places in a city, electric bicycles might be a better alternative. When vehicles like this are introduced, humanity is one step closer to creating more energy efficient societies.

Research could be extended from what has already been done. For example, in this project, the amount of electrical energy output from the battery was never measured. This could be done through determining the charge of the battery in Watts before the bike ride and then after the bike ride. This would show the total energy expenditure of the electric bike’s battery. This can be predicted to be the difference between the regular bike rider’s manual power and the electrical bike rider’s manual power. If the electrical bike rider’s manual power (e) was subtracted by the regular bike rider’s manual power (b), it would be an estimate to the electrical assistance (ea).

b - e = ea

The battery for the e-bike continues to be a center of study to improve this mode of transportation.

Likewise, studies also need to be done to make electrical bikes more marketable in the United States. To do this, electrical bikes will need to become cheaper. As of now, electric bikes can cost thousands of dollars. The battery is the most expensive component of an electric bicycle. Since many of these batteries are made from materials such as lithium and lead, research concerning a new battery that would be less expensive could be done. Also, battery charging and overall efficiency need to be better as well as the weight of the electric bicycle. Many steps still need to be taken into this field of study. This research is only a gateway into the future of electric bicycle studies.

VI. CONCLUSION

The future of e-bike research is bright. This study acts as a segway to future areas of research on this subject in terms of bike efficiency. This in turn could help to pave the way for e-bikes to become a more popular mode of green transportation in the future. This being said, it is important to note that e-bikes must be improved upon before they can this stage. Projects such as the previous one conducted by Dr. Chris Cherry and the one that this paper concerns not only add to the research surrounding e-bikes, but they also create awareness of the benefits of e-bikes and their uses. By raising awareness of e-bikes, this project pushes for a future that includes yet another form of green transportation that will work to preserve our environment.

VII. ACKNOWLEDGEMENTS

This work was supported in part by the Engineering Research Center Program of the National Science Foundation and the Department of Energy under NSF Award Number EEC-1041877 and the CURENT Industry Partnership Program.

Other major contributers to this work were Kwaku Boakye, Dr. Shashi Nambisan, and Dr. Chris Cherry. All of these people helped to guide this research in the right direction.

VIII. REFERENCES

Behrendt, Frauke. "Using Electrically-assisted Bikes: Lazy Cheaters or Healthy Travellers?" The Guardian. N.p., 14 May 2013. Web. 1 July 2015.

"E-Bike Sharing at UTK." E-Bike Sharing at UTK. N.p., 2012. Web. 02 July 2015.

"EDUCATION & ENFORCEMENT."Pedestrian & Bicycle Information Center.U.S. Department of Transportation Federal Highway Administration, n.d.Web. 02 July 2015.

"Electric Assisted Bicycle Use on Multi-Use Paths." Electric Assisted Bicycle Use on Multi- Use Paths. N.p., n.d. Web. 01 July 2015.