Scooterizers Team Project

Transcription

1 Scooterizers Team Project Making last-mile transportation safer, easier, and more efficient. A Mid-Project Report for the summer 2010 senior design project Submitted by: Colin Gordon. Majed Alateeq. Jon Teske. Jaeheung Park.

2 Table of Contents Table of Contents Executive Summary Introduction 1.1 Background Problem Definition Capabilities & Risks Concept Considered 2.1 Frame Throttle Motor Regenerative Braking Clutch Electrical and Control Systems Control Systems (A) Jet-Tread Controller.. 10 (B) Commercial Motor Controllers.. 11 (C) Homebrew Design..11 (D) Jet-Tread Controller, with Improvements Electrical Systems (A) Parallel-Charge Series-Discharge Ultra-Capacitor Bank (B)Drive System Design.13 (C)Regeneration System Design...13 (D) Electrical System Improvements and Series-Parallel Switch Concept Selection 3.1 Brushless DC Motor Xootr Frame Micro Controller Series/Parallel Switch System Architecture 4.1 Model the Electrical System Improve Voltage Regulation and Protection Circuits Improve the Parallel-Charge Series-Discharge Ultra-Capacitor Circuit Combine the Fragmented Control System Add a Functional Variable Throttle and Variable Regenerative Brake Add a Clutch to the Motor System Future Work..18 Scooterizers Page 2

3 EXECUTIVE SUMMARY As part of our first semester Senior Design project, team Scooterizers have studied both the old Jet- Tread s team project as well as completed individual research and study. We ve explored the scooter frame, motor, storage system, electrical and control systems, and human input systems such as brake and throttle controls. The team has come to the conclusion that it is best for both the short and long term that we work on improving and adding functionality to the Jet-Tread project design, rather than a complete redesign of large portions of the system. For this conceptual design, team Scooterizers will complete the following: Model, diagram and document the Electrical System Complete or refine circuit protection for the electrical and control systems Simplify the current parallel-charge series-discharge capacitor circuit Combine the multiple fragmented control circuits Add a functional variable throttle and variable regenerative brake Add a clutch to the motor system Key features and project deliverables for the improved design will include: Clear, detailed and concise SPICE models and circuit diagrams for the electrical and control systems. Addition of working overvoltage protection to the electrical system, and proper voltage regulation for the control systems Addition of an automatic microcontroller and FET/relay based series-parallel switching system for the capacitor network Centralization of the control system onto a single, master microcontroller Ability to use the prototype as a normal kick scooter with intuitive hand controls for the user, which is not possible with the current system The merits of the design will include much enhanced user ability to control and use, higher efficiency, reduced chances for circuit failure, and a knowledge database that will be passed to future teams. We ask that you review our design decision and return your written approval for both our conceptual design path and our budget. To ensure the best possible outcome for this project, we also ask that you allow us to use Guillermo Conde as an EE consultant for next semester. Scooterizers Page 3

4 1.0 INTRODUCTION 1.1 Background: Most people who live in urban cities are using transportations as busses, trains, cars, and motorbikes. Big cities have a complex parking problem, so they are necessarily to walk few blocks to get home, school, or work. People can walk the distances easily, but many people are using scooters or bicycles to reduce the time spent in moving. Electric kick scooters can make the distance short and save the moving time. Most the existing scooters weight more than 30 lb and take several hours to charge their batteries. Thus, the electric kick scooters have to be simple, cheaper, and lighter. Also, foldable scooters are needed for convenient carrying and saving. There are several successful companies producing both electric and kick scooters, indicating that there is an established market acceptance for the products and enough demand to encourage competition. 1.2 Problem Definition: Current electric scooters are heavy, expensive and not efficient to ride up hill. The team Scooterizers was posed with a problem; building a scooter to be used in uphill efficiently. The goal of this project is to develop a portable kick scooter with tough, efficient and powerful electrical drive and storage systems for urban transportation needs. The project takes advantage of energy scavenging. The prototype vehicle will incorporate regenerative braking and energy storage via ultra-capacitors to provide power assisted riding without having to charge batteries. The team Scooterizers have done a lot of research to determine how electrical scooters work. The team spent reasonable time researching and learning to determine the specifications of the desired prototype. The team examined different scooter frames to find the best choice. Also, we interviewed several specialists in electrical and mechanical engineering fields. The clients, Dr. Greg and IVUS innovation Inc. were a critical part of the project learning stage. The performance expectations for the desired prototype are as follow: Performance expectations: Minimum Efficiency: 51%. Scooter Weight: 20 lb. Scooterizers Page 4

5 Total scooter cost: $ 750. Human Input: 1. Twist Throttle. 2. Handbrakes. Energy Storage: Ultra-Capacitors. The time constrain has prevented us from doing more work on the project. When exploring what we can do to reach the goal of this project, we found several ideas such as in-hub motor. However, since we have only six weeks to present a solution to this problem, we decided to give time a higher priority and present the chosen design. By the end of the project, the client will be delivered with a scooter prototype, knowledge database, and final report that give all the details about the project and any other associated materials such as a well written manual to help in using the scooter. 1.3 Capabilities & Risk: During our project learning phase, we have identified a need for knowledge/ experience in the following areas for our chosen conceptual design. Electric motors Ultra-capacitors Microcontrollers Embedded Programming (C or C++) Mechanical Clutch Design Electric Circuit Modeling Electric Circuit Design PCB Design and Fabrication Wiring Harness Assembly The Computer Engineering expertise on the team has skills gained from various coursework projects, including Microcontrollers (ECE340) and Real-Time Operating Systems (ECE452) that will be necessary to complete any embedded programming design and microcontroller implementation. PCD design and fabrication is a skill we intend gaining during the course of the Scooterizers Page 5

6 project. There are many PCB resources and sources of knowledge available at the University of Idaho, which we intend to access. The Wiring Harness Assembly and Mechanical Clutch Design will be carried out by the ME s on our project team. They have experience with mechanical design from relating from their coursework. One of the risks to the current project is the lack of EE expertise and knowledge. Electrical Circuit Modeling, Electrical Circuit Design, Ultra-capacitor implementation and Electric Motor implementation have been partially achieved by the last team. However, the Scooterizers will rely on either the addition of an EE team member, or design oversight from EE faculty or staff to ensure the best possible outcome for the EE oriented project design aspects. We have studied various designs and implementation widely available at both the University as well as through online resources. We ve also has access to an EE graduate student who has helped us reverse-engineer the previous team s EE designs. We have the original scooter and test ultra-capacitors. We plan on using all tools we have at our disposal, including mechanical design labs and the power labs, design software, IDEs, microcontroller debugging and development boards and tools, faculty, staff, IVUS and others for advice and design expertise. 2.0 CONCEPT CONSIDERED 2.1 Frame: There are several scooters which are suitable for last mile transportation and are currently marketed such as Razor, Go-Ped, Xootr, and Side Walker Micro. Choosing the proper frame will strongly influence other parts decisions, so numerous different frames were considered with factors such as cost, weight, strength, size, and top speed between scooters. Old team, Jet-Tread, chose the Xootr as their frame because of its superior rolling resistance, comfortable ride, frame simplicity, and reasonable price. The GoPed was cheaper, but was the only category which exceeded that of the Xootr. The Razor frame was considered for an early prototype due to its low price, but the Xootr s uncertainty of rolling resistance and durability. Our team has looked at the Side Walker Micro. From our frame decision, there were no big difference between the Xootr and the Side Walker Micro. Also, one of our goals is to make the Scooterizers Page 6

7 scooter lighter than 15lb and to support maximum weight of 250lb. The frame of Xootr is strong enough to support those facts, and the Xootr is the best folding mechanism with low rolling resistance. Therefore, our final decision was to reuse the Xootr from old team because it is waste money to buy the new frame. 2.2 Throttle: Most scooters use either thumb throttle or twist throttle. There are no technical differences between them but people s preferences. Some people are familiar to use thumb twist throttle, but others prefer to use the twist throttle. Our goal is to make improvement from old team s scooter. Old team used the thumb throttle with rubber band. If the rubber band tears off, the twist will not work. It doesn t look good either. So, our choice is to use twist throttle instead thumb throttle. 2.3 Motor: Several types of electrical motors have been examined during project learning stage. We started by analyzing the motor that used by team Jet-Trade which was Brushless DC motor. After that we went to other types of motor such as; In-hub motor and alternate electric chain drive motor. Brushless DC Motor: These motors are permanent magnet motors which use a special controller to send pulses to their windings in phase with the motor speed. Magnets on the rotor spin due to the effect of the magnetic field generated by the coils. There are two types of BLDC motors: Outrunners, which have the rotor outside the windings on the stator, and Inrunners, which have the rotor inside the stator windings. BLDC motors are commonly used on electric airplanes and have high peak efficiencies (80%-85%) and higher torque than brushed DC motors. They are fairly inexpensive if purchased from a hobby vendor 400W=.54hp without controller). We selected this motor not only because it was used by Jet-Trade team. BLCD has higher torque and it allows for mounting the motor in the wheel which will be left to the next teams if the decide to do some improvement on the motor In-Hub Motor: Scooterizers Page 7

8 In-hub motor is an electric motor that is incorporated into a hub of a wheel and drives it directly. In hub motor provides high efficiency for a system which is one of the biggest advantages of Inhub motors. However, the group decided that this motor will not be the best choice regarding the motor because of its high weigh and cost. The lack of knowledge regarding this new technology is a disadvantage of using it. Other motors: There are several types of motors can function very well in terms of prime mover. Coil or linear springs are less complicated and have higher efficiencies than BLDC. However, they have unacceptable energy densities making them unsuitable for this application. Other options are IC engines and single expansion compressed air engines. They have higher densities but their efficiencies are bad at high pressures. 2.4 Regenerative Braking: Although regenerative braking has been around for years it has never been commercially applied to the electric scooter market. The idea of capturing energy from braking and storing it as electrical energy falls under the general concept of energy scavenging. There are multiple ways that we could capture the waste energy from the scooter but the most obvious choice would be to use the motor as a generator. If you had no electricity coming into the motor the rotation of the wheels would power it as a generator, which would add resistance to the forward motion of the scooter until the rider came to a stop. Meanwhile the energy being captured by the generator would be sent back to the ultra capacitors as electricity to be used by the motor later. It makes the most sense to use this type of regenerative braking as the primary brake for the scooter and as our primary method of energy capture. As the design process progresses we will continue to explore ideas of capturing energy from wind with fans/turbines, capturing energy from the sun with small solar panels, and even capturing energy from acceleration and vibrations with spring-magnet induction systems like those found on rechargeable flashlights. 2.5 Clutch: If we decide to stay with the current motor or even chose a different electric motor with a chain drive, we will need to incorporate some type of clutch to disengage the rear wheel from the motor. One of the best parts about riding a scooter is the feeling of coasting forever on a single push. With the current design the rider can only attain this feeling by manual Scooterizers Page 8

9 removing the chain from the motor because of the resistance the motor adds when it isn t power. Our first instinct was to go for the In Hub motor to avoid the need for a clutch altogether. Since we are no longer pursuing that design we have just begun to explore other possible solutions to this clutch problem. The most obvious choice would be to find a small centrifugal clutch as they are common in many power tools, chainsaws, and lawnmowers. Centrifugal clutches are nice because they are small, relatively lightweight, and automatically engage. The one problem that immediately becomes apparent is that a centrifugal clutch will not work with in conjunction with a regenerative braking system as the clutch will automatically disengage as the scooter decelerates. One possible option would be to integrate that type of clutch with one similar to those found in Yo-Yo s. A Yo-Yo clutch is only disengaged at high speeds when the centripetal force from spinning causes weights to move away from the axis of rotation and the clutch releases the central spindle. This type of clutch by itself would limit the top speed of the scooter and would only be able to regenerate at low speeds so it s obviously not a good choice. Some type of hybrid clutch that could accomplish both low speed regeneration while moving and low speed disengagement while pushing and coasting would be necessary for this particular application. This means that, other than a complicated mechanical clutch that we would have to design and build ourselves, the best option would probably be an electromagnetic clutch that could be turned on and off with a switch or sensor. 2.6 Electrical and control system: The team explored a number of different design options for the electrical and the control systems. Below is a list of the result of our project learning: Control Systems: The control system is what allows interaction between a user and the electric motor. Functions of a control system include power management, speed controls, and safety. Scooterizers Page 9

10 (A) Jet-Tread Controller: The current Jet-Tread controller is made up of four distinct components (see diagram below). Figure 1 - Jet-Tread Controller The speed controller takes power from the ultra-capacitor bank and translates it into a threephase signal that runs the motor. The speed the motor runs at is controlled by a signal from the motherboard, which in turn translates a signal from a thumb-throttle attached to the frame. The sole purpose of the relay driver is to run 150mA of current to the relay switch, which acts as a safety feature to switch the ultra-capacitor bank on/off based on throttle input. The function of the daughterboard has been difficult to ascertain, but we believe it is supposed to act as a currentlimiter that doesn t actually function. Scooterizers Page 10

11 (B) Commercial Motor Controllers: There are many commercially available motor controllers for DC, AC, and BLDC motors. Most BLDC controller offer a variable of outputs and inputs, including Hall- Sensors, built-in throttle controls, regenerative braking, and programming ports. Good examples of such controllers can be found at (click Hub Motor and go down to the bottom of the page). Most commercial controllers are very easy to use and integrate into exiting projects and designs. However, they can also be very difficult to debug and come with little documentation. (C) Homebrew Design: Searching the internet yielded a plethora of homebrew designs for engineering projects or hobbyists. Large microcontroller manufacturers write extensive white papers and application notes for applying their controllers to BLDC motors. There are also extensive design knowledge resources from numerous do-ityourself web pages and manual. This type of project would be very, very useful to do at the University of Idaho, where lots of projects are based upon DC motors. However, implementation time is the highest concern when it comes to this type of design. (D) Jet-Tread Controller, with Improvements (Team Pick for Future Work): For our conceptual design, we chose to work with the current Jet-Tread design and make several needed improvements. One circuit-safety concern is proper voltage regulation: due to lack of documentation, we cannot verify that the voltage regulation for the PCB boards on the controller is doing the job correctly. The previous team mentioned they had board burnouts under certain conditions, and Guillermo Conde believes that strengthening the voltage protection would eliminate this threat. Also, we can reduce the number of discrete boards from three down to one without much effort. Proper system design with current needs and limitations in mind will provide a much improved controller circuit. Scooterizers Page 11

12 2.6.2 Electrical Systems: The electrical system provides the energy propulsion and generation systems for the project scooter. The electric system can be broken down into three discrete (but interconnected) components, all based on the Jet-Tread design. (A) Parallel-Charge Series-Discharge Ultra-Capacitor Bank: Jet-Tread implemented a manual parallel-charge series-discharge system to maximize the electrical energy storage characteristic of capacitors (capacitance adds when in series, which leads to higher storage when charged this way). Discharging the ultra-capacitors ensured that the voltage of each ultra-capacitor added, much like batteries do when placed in series. This allowed the speed controller to see a high-enough incoming voltage to power the Jet-Treads BLDC motor, which operates at 12 Volts. Unfortunately, the manual switching system is difficult to use, as it requires a screwdriver to operate, and around five minutes to achieve correctly without shocking the user. Figure 2 - Manual Parallel-Charge Series-Discharge Switch Scooterizers Page 12

13 (B)Drive System Design: The drive system design consisted of the ultra-capacitor bank, a relay, a non-working current-limiting daughterboard, and the speed controller (see Figure 1 - Jet-Tread Controller). When fully charged, the ultra-capacitor bank delivers around 26 Volts to the speed controller. While this design works, it leaves voltage regulation up to the speed controller. Further exploration of the speed controller datasheet is needed to see if the controller is supposed to handle this amount of overvoltage. (C)Regeneration System Design: Jet-Treads voltage regeneration system turns the BLDC motor into a generator, thereby acting both a power source and a braking force for the user riding the scooter. The regenerative braking system is automatically activated when the capacitor bank is in parallel mode. When the scooter moves, the motor turns at a higher voltage level than the capacitor bank and the capacitors are charged. In the Jet- Tread design circuit, there is an overvoltage protection board that senses when the ultracapacitor bank is fully charged, then dumps all braking power to a resistor bank. This prevents destroying the ultra-capacitors by overcharging them. Unfortunately, there is no protection for the speed controller, which is still attached during charging. The motor spinning too quickly (going down a steep hill) results in the motor controller overheating and destroying itself. See Figure 3 - Jet-Tread Regenerative Circuit Design below: Figure 3 - Jet-Tread Regenerative Circuit Design Scooterizers Page 13

14 (D) Electrical System Improvements and Series-Parallel Switch (Team Pick for Future Work): We believe that by adding circuit-safety controls to the regenerative circuit, we can drastically reduce the changes for destroying the speed controller. We also intend to design an automatic series-parallel switching device for the ultra-capacitor bank using relays/fets and a microcontroller. This will dramatically increase the usability of the scooter. The drive system also needs a good review, and we may place a currentlimiting power supply between the ultra-capacitor bank and the speed controller to eliminate overheating and overvoltage concerns. 3.0 CONCEPT SELECTION We have investigated several design options for the key functions identified for a power assisted kick scooter. Finally, we have selected a preferred design option but we haven t had the opportunity to test platform of a power assist scooter due to time constrain. One of the requirements of this project is to keep working on and to improve Jet-Trade s design. The conceptual design is based on the previous team work. It is because the project is continuation of last team work so we decided to take advantage of what has been done. We went closely and carefully over the last team documents to see where we can improve the project. The group ended up having many ideas about building a better electric scooter starting from Jet-Trade s prototype. The team Scooterizers will focus on building a knowledge database for the benefit of the project itself and the coming teams. That is because we struggled with last team weak documentation. In summary of the design, the team Scooterizers will be working on the following: 3.1 Brushless DC Motor: It was used by the team Jet-Trade. We were debating on replacing it with In-Hub motor to increase the efficiency. However, due to time constrain and lowering the cost, we agreed on keep the same motor. Efficiency can be improved by working on the other parts such as controller and series/ parallel switch. Scooterizers Page 14

15 3.2 Xootr Frame: It is collapsible, lightweight and cool. It has also the best folding mechanism and low rolling resistance. We can by using Xootr modify the deck if needed. Variable regenerative brake and throttle will another part when working on the frame. 3.3 Microcontroller: The previous prototype has four small controllers. Each of them has a specific job to do. We are planning to combine all these in one master microcontroller and we may get rid of unnecessary ones. 3.4 Series/Parallel Switch: Instead of going from series to parallel manually, we will automate this process by improving the circuit design. We already have different ideas for that but unfortunately we haven t had the opportunity to do that due to time constrain. The selected design explains how we will improve the last team s prototype. We, as a team, came to a conclusion after a long discussion that what has been done is very advantageous if we work on improving it. We decided to take the same path that has been taken by the previous team. By doing that, we will reduce the cost of the project and we don t have to throw away about 80% of last team work. 4.0 PROJECT DELIEVERABLES For our conceptual design, we propose to improve on the Jet-Tread s design in the following ways: Model, diagram and document the Electrical System Complete or refine circuit protection for the electrical and control systems Simplify the current parallel-charge series-discharge capacitor circuit Combine the multiple fragmented control circuits Add a functional variable throttle and variable regenerative brake Scooterizers Page 15

16 Add a clutch to the motor We believe our design has the potential to meet or exceed your specifications in the following ways: Cost: Improving on the old design is less expensive and a better use of resources than overhauling the design completely. Weight: Keeping the old motor and frame will result in less weight being added to the system. We should be able to maintain the previous team s final weight (<20lbs). Efficiency: Improving the old electrical and control system design should result in overall higher system efficiency and less chance for circuit failure. Human Input: Automating the step between propulsion and regenerative braking will allow for much easier usage by the rider. The Scooterizer design will also implement intuitive propulsion and braking systems. Ease of Use: The clutch assembly will allow the scooter to be used like a normal kick scooter, which will be a huge improvement on the old design, where the motor cannot be disengaged from the wheel. A more detailed discussion of the team deliverables can be found below: 4.1 Model the Electrical System: We propose to model each component of the electrical system, including voltage, current, power, Ultra-capacitor transients, and overall circuit diagrams. We will present these findings to you in highly-readable lab-research format at the end of the project in both written and software forms. This will not just be a project deliverable, but also an essential step in ensuring thoughtful and successful design for the electrical and control system components. 4.2 Improve Voltage Regulation and Protection Circuits: We will add proper voltage regulation and protection to the Jet-Tread design. For the control system, we will develop a proper voltage regulation circuit for the new master controller. For the propulsion system, we may (depending on the speed controller characteristics) add a voltage regulation circuit in between the ultra-capacitor bank and the speed controller. On the regenerative circuit side, we will add a MOSFET gate system to isolate the speed controller from the motor when the system Scooterizers Page 16

17 is in regeneration mode to prevent destruction of the speed controller. We also will replace the low-resolution voltage comparator chip that prevents the ultra-capacitor bank from overcharging with a high-resolution microcontroller ADC. We will also improve Jet-Treads safety drain system, which dumps power from the ultra-capacitors to resistor bank. This is because we cannot find models to this system anywhere, or reasoning as to why they used the resistive load that they did. 4.3 Improve the Parallel-Charge Series-Discharge Ultra-Capacitor Circuit: We will build a microcontroller-based design using MOSFET gates or relays that will greatly improve the user s ability to use the scooter. We will also implement a fuse system in the ultra-capacitor bank to prevent overcurrent. 4.4 Combine the Fragmented Control System: We will combine the fragmented control system to be handled by a master microcontroller. This will greatly reduce the complication of the control system, which will lead to less circuit failure and better documentation. We also hope to reduce the size of the system by managing the controls from one PCB rather than three. At the end of the project, we will give you a complete control system user guide, with system diagrams, complete software code, and instructions for the next team so they can program and add functionality to the control circuit as they please. The type of microcontroller we intend to implement will have extra IO points for future functionality expansion. 4.5 Add a Functional Variable Throttle and Variable Regenerative Brake: We plan to implement a variable throttle and variable brake system in conjunction with the master controller. This should easy to implement right into the master control circuit rather from a separate circuit board. 4.6 Add a Clutch to the Motor System: We will add a clutch system to the current electric motor so that users may use the scooter as a normal kick scooter. This will ensure that the motor or regeneration system is only engaged when the user wants it to be. Scooterizers Page 17

18 5.0 FUTURE WORK At this time, we recommend that you review our design decision and return your written approval for both our conceptual design path and budget. To ensure the best possible outcome for this project, we also ask that you allow us to use Guillermo Conde as an EE consultant for next semester. We believe we can improve over the Jet-Treads project while still using their hard work and engineering design. We can provide a functional prototype to the end user, as well as provide an effective an enjoyable use for ultra-capacitor technologies, and an excellent knowledge database that future teams may use. We believe we will satisfy your specification in the following area: Weight Human Input Energy Storage and Propulsion System Ease of Use Anticipated problems include final scooter cost and efficiency. We believe that future design teams will better be able to reduce cost and increase efficiency. Our anticipated work schedule can be found below: Finalize Design Strategy Electrical System Modeling Individual Designs Fabrication Assembly Final Assembly Scooter Validation Documentation Knowledge Database Late July/Early August August/Early September September/Early October October/Early November [November/December] Scooterizers Page 18