FIRST Robotics Optimized Drive Train System

Transcription

1 FIRST Robotics Optimized Drive Train System Design Team Nicole Byrne, Michael Conry, Steven Fernandez, Brandon Holley Design Advisors Prof. Yiannis Levendis, Prof. Donald Goldthwaite Abstract The purpose of this capstone project is to create an optimized drive train that the Northeastern FIRST Robotics team, the NUTRONs, may implement to their competition robot for the 2010 season. Each year participants in the competition design drive trains for their robot without sufficient time to properly analyze and digest their design. It is the intent of this capstone group to complete analysis and calculations on the structure, gears, shafts, chains and hardware of a previous NUTRON design to find areas of improvement for the drive train. This data will be used to provide suggestions for a better drive system and new concepts for designs that the team could use in future competitions. Past FIRST experiences from the NUTRONS and patent information for drive trains will be taken into consideration when looking at new designs. Also the rules of FIRST for size, cost and limitations on parts, will be followed so that the design will be applicable to an actual FIRST competition. This team has decided to design and build an omni-directional drive train system that will allow the robot to move in all directions without the need to turn. The design consisted of four omni-drive modules, two steering gear boxes, two power gear boxes and an easily assembled frame.

2 The Need for Project To thoroughly and scientifically analyze an omni-directional drive train system for the high school robotics team the NUTRONs. The FIRST competition is a high school robotics competition that is put on in the spring of each year around the world. Teams of high school students are given the competition rules in January of each year and are then given six weeks to design and build a robot that can compete in a game that is selected for the year. High school robotics teams, like the Northeastern University sponsored NUTRONs, work with adult mentors, either in college or in industry, to solve the engineering problems associated with building a robot to meet certain weight and size limitations along with limited motor selection and battery options. Due to the volume of tasks that each team must overcome, it is often difficult for teams to foster innovative designs for their drive train, which is the most integral part of the robot since it provides motion and houses electrical components. Since teams are allowed to research in the off season, it is the intent of this capstone project to help the NUTRONs be more innovative with their drive train design by designing and building an omni-directional drive base as a proof of concept for the upcoming 2010 season. An omni-directional drive has never been attempted before by the NUTRONs, so the work and research done in this project will further enhance the teams technical knowledge and capabilities. The Design Project Objectives and Requirements The objective of the project is Design Objectives to design, build and test and The objective of this project is to provide the NUTRONs omni-directional drive base as with a thorough and scientific investigation into the feasibility of a proof of concept for the an omni-directional drive train that the team could potentially NUTRONs. use in the 2010 robotic season. This will be accomplished by first designing a working omni-directional drive base as a proof of concept. Then analysis will be performed on the design to ensure that it will work. After analysis is performed a working prototype will be constructed and tested versus a previously

3 successful NUTRONs drive system to determine the enhanced capabilities of the omni-directional system. Finally the project conclusions will be passed along to the high school students on the NUTRONs to expand their technical knowledge and robotic capabilities. Design Requirements The omni-directional drive base will need to travel at 12 ft/s. This specification was based on limited motor selection and previous FIRST competition experience that the 12 ft/s is a good controllable game pace for a robot. The omni-directional drive base will also need to weigh less than 50 pounds. In the FIRST competition, the entire robot must not weigh more than 120 pounds without a battery, so limiting the drive train weight to 50 pounds allows for more weight to be used on the game components of the robot and the electronics system. Design Concepts considered Due to the variety of methods for omni-directional systems, a couple decisions had to be made on the method of motion and power supply to lead to the final design. Wheel Mounted Power There are a variety of methods that can be implemented to create omni-directional motion. Our group chose the method that was the most feasible for the NUTRONs to build based on complexity, weight and cost considerations. Fixed Axle vs. Free Axle The first decision the group had to make was between a fixed and free axle system. A fixed axle system is when the wheels are fixed in place and a special wheel with rollers is used to achieve omni-directional motion. The free axle system allows the wheels to rotate in the direction of motion with the use of wheel modules that use simple wheels and bearings to turn the wheels in the desired direction of motion. The free axle system was chosen because it not only had increased agility over the typically used skid steer system but it also had minimal frictional losses in the wheel to floor interface, increased pushing power and used simple wheels.

4 Wheel Mounted Power vs. Chassis Mounted Power After choosing a free axle system, the next decision was how to power the wheel modules that would be used. Wheel mounted power is when the motors are mounted on the wheel with a housing structure. The problem with this system is that it is very heavy and limits the wheel sizes that can be used. The chassis mounted power is when motors are mounted remote Chassis Mounted Power from the modules on the frame. This results in a lighter module but a more complex chain system to transmit power. Due to the lightness of the chassis mounted power, this group chose to move forward with this for the design. Recommended Design Concept Co-axial module design with The decisions for a free axle system with chassis mounted separate power and steering power led into the group s design of a co-axial swerve drive gearboxes housed in a bi-layer system. The components of the system are the co-axial swerve box beam frame module, power and steering gearboxes and a bi-layer frame. Co-axial Swerve Module The three critical design factors for the co-axial swerve module were the chain paths, moment loading and 90 degree power transmission. The co-axial shaft was designed to alleviate any issues with the chain paths. The chain from the power gear box will run to the top sprocket of the module and then be transmitted through a vertical hexagonal shaft that runs down the center of the coaxial shaft. The steering gearbox chain will run on the bottom sprocket which is connected to the outer shaft of the co-axial Co-axial Swerve Module shaft. The out shaft is connected to the module through the use of a bearing that will be used to turn the wheel in the direction of motion. To handle the moment loading on the module from the friction with the ground, two bronze sleeve bearings were implemented. These bearings were custom machined to fit into the design. The bronze bearings were chosen because they were the most economical for this low rpm application.

5 Power Gearbox Steering Gearbox Frame Design The 90 degree power transmission was achieved with the use of miter gears. The miter gears transmit the power that is delivered to the vertical shaft onto another horizontal hexagonal shaft that is held into place with roller bearings. Final reductions are done with the use of chain and sprockets to turn the wheel at the desired speed. Power and Steering Gearboxes The power gearbox uses two motors with an output speed of 5500 rpm. In order to achieve a speed of 12 ft/s, an 8:1 gear reduction is necessary. To eliminate the use of multiple gears the decision was made to complete a 4:1 reduction in the power gearbox and the final reduction would be performed in the module with the use of chain and sprocket. The steering gearbox uses one motor with an output speed of 100 rpm. In order to turn the module at a rate of one turn per second, we needed to reduce the speed to 60 rpm. This reduction was completed with the use of chains and sprockets. Frame The frame was designed to house the modules and gearboxes. For ease of assembly/disassembly the frame members were spaced to allow for the modules and gearboxes to be dropped in from the top and then bolted down. The bilayer design protects the module and gearbox components. Financial Issues Budget of $ for entire drive train Aside from what is provided in the kit, each FIRST team is allowed to spend up to $3500 on other components. This includes the estimated cost of donated parts but excludes the cost of donated time. Due to this limited budget for the entire robot this group chose an estimated cost goal of $ for the drive train.

6 Recommended Improvements Future improvements to reduce weight and cost While the drive train was designed to the best of our abilities with the allowable time and resources, areas of improvement exist in weight and cost reduction Top of Robot (Turret) Omnidirectional Drive Base Exploded View of Robot Concept with Omni-Directional Drive Base