The Drivetrain Project

Topics

  • Project Description
  • Requirements
  • Basics
  • Drivetrain Types
  • Testing
  • Science/Engineering
  • Conclusions

Presentation of the Drivetrain Project:



Project Description:


In this project we are trying to test different drivetrains to see which designs excel in each category. We will use a standard frame and apply a weight to the designs to simulate different robots. In addition to this, we will utilize and test various wheel types and motor combinations. During our trials, we will simulate the distinct environmental factors present in each annual First Tech Challenge game in order to discover the most optimal drive system for each specific game strategy.

Requirements

The drivetrain can define a robot and is the most important element of a design; the strength of the robot's drivetrain can heavily influence its overall performance.

The drivetrain must:
  • žmeet your strategy goals for the game
    • speed: The robot must be able to surpass the competition in any direction at any time.
    • traction: The robot must be able to effectively grip the various field elements without damaging the playing field or limiting maneuverability.
    • maneuverability: The robot must be able to quickly navigate the field, rotate on its axis, and escape out of harm way (WARNING: LASER CANNONS PRESENT ON FIELD).
    • power: The robot must be able to conserve power usage to ensure maximum overall performance during a match.
    • offense/defense: The robot must be able to meet strategic objectives depending on team preference.
    • weight: The robot weight should maximize motor efficiency without compromising defensive/offensive abilities.
  • žbe built with available resources
    • budget: The drive train construction costs should not exceed the team-defined boundaries of the budget.
    • tools required: The drive train should be designed to be built only with tools that each team actually has. (No rocket boosters unless you are sponsored by NASA)
    • time: The drive train should be easily assembled/dissembled for maintenance within a short time span.
  • žrarely needs maintenance
    • durability: The drive train should be constructed to last so that repairs are minimal. The drive train must be protected from harm.
    • testing: Thoroughly test the drive train during construction to ensure that it can handle match conditions.
  • can be fixed within 4 minutes
    • easily replace motors between matches
    • easy to access critical components
  • Uses minimal amount of space
    • The drivetrain fits in designated space allotted by the system envelope


Basics

Brainstorming and Design resources:
  • žDecide strategy after kickoff. What will you focus on?
    • Speed:
    • Power
    • Mobility
  • žDecide how many motors you will use on drivetrain
    • 4 motors is ideal (2 weakens a design and 6 causes connection issues)
    • chain/gear motors together to maximize power
    • Wire motors on separate ports on motor controllers to maximize power
  • žRobot weight
    • What weight will maximize
      • traction
      • mobility
      • speed
      • defense (limit other robots pushing while playing offense)
  • žDurability
    • put the drivetrain under stress to test the durability.
    • identify weak points and correct them
    • driver practice
    • spare parts and assemblies
  • žDevelop a project plan
    • allot time for design, build, testing, software and driver practice
  • žTechnology
    • motor capabilities and limitations
    • AndyMark NeveRest 40 Motor (am-2964)
      • Performance Specs:
        • Gearbox Reduction: 40:1
        • Voltage: 12 volt DC
        • No Load Free Speed, at gearbox output shaft: 160 rpm
        • No Load Free Speed, motor only: 6,600 rpm
        • Gearbox Output Power: 14W
        • Stall Torque: 350 oz-in
        • Stall Current: 11.5 amps
        • Force Needed to Break Gearbox: 1478 oz-in
        • Minimum torque needed to back drive: 12.8 oz-in
        • Output pulse per revolution of Output Shaft (ppr): 1120 (280 rises of Channel A)
        • Output pulse per revolution of encoder shaft (ppr): 28 (7 rises of Channel A)
      • Performance Specs, mounted to AndyMark dyno:
        • Max Speed (under load of dyno): 129 rpm
        • No Load Current (under load of dyno): 0.4 amps
        • Stall Current: 11.5 amps
        • Stall Torque: 396 oz-in
        • Max Output Power: 15 Watts
        • Time to Failure at Stall: 2 minutes, 54 seconds
        • Motor Case Temperature at Failure: 190 degrees F
    • electrical capabilities and limitations
      • Each motor controller should only power 1 drive train motor.
      • Never connect more than motor to as motor controller port.


Drivetrain Types:


2 Drive wheels, 2 Motors with 2 Omni Wheels

2 Drive wheels, 2 Motors with 2 Omni Wheels

4 Drive wheels, 4 Motors - Not Connected

4 Drive wheels, 4 Motors - Not Connected

4 Drive wheels, 4 Motors - Connected

4 Drive wheels, 4 Motors - Connected

10 Drive wheels, 4 Motor - Connected

10 Drive wheels, 4 Motor - Connected

6 Drive wheels, 4 Motor - Connected with 4 Omni Wheels

6 Drive wheels, 4 Motor - Connected with 2 Omni Wheels

Track Drive, 4 Motors - Connected
Track Drive, 4 Motors - Connected

Holonomic, 4 Motors - Not Connected

Holonomic, 4 Motors - Not Connected

TWA-1 6 Wheel drive, 4 Motors Connected with 4 Omni wheels

TWA-1



Testing:

Straight Line Speed Test


The Straight Line Speed Test tested the robot on how fast it would travel 16 feet.
  • The drive area had a starting area to allow the robot to reach full speed prior to the course.
  • The drive field used standard FTC field tiles.
  • Total robot amps were recorded for each run.
  • Time to drive the 16 feet was recorded for each run.
  • At least 4 testes were recorded for consistent results
  • The robot was weighted for the base weight
  • 10, 20, 30 and 40 pounds were added to the robot for each run

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Here I was setting up our 4 Wheel + Chain robot for the straight line test. -Melea

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Test robot in straight line test starting position. -John Paul

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The Holonomic drivetrain was difficult to set up to travel in a straight line. -Melea

Pull Test


The Stall Test tested how much weight the robot could pull
  • The drive field used standard FTC field tiles.
  • Total robot amps were recorded for each run.
  • Time amount of weight lifted was recorded for each test.
  • Lift was added until the wheels slipped or the motors stalled
  • The robot was weighted for the base weight
  • 10, 20, 30 and 40 pounds were added to the robot for each test

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This is our Tank drivetrain before the pull test. -Melea

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Here you can see the pulley with added weight for the robot to pull. -Taylor

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Here we waited for weight to put on the track robot. -Wesley

Side Drag Test


The Side Drag Test tested how much weight it took to pull the robot sideways.
  • The drive field used standard FTC field tiles.
  • Time amount of weight to pull the robot was recorded for each test.
  • Weight was added until the robot was pulled sideways
  • The robot was weighted for the base weight
  • 10, 20, 30 and 40 pounds were added to the robot for each test

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Here we attached the weight to the center of the drivetrain with it facing perpendicular to the force applied. -Melea

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Here you can see the added weight positioned on our 4 wheel chain drivetrain. -Wesley
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We added further weight to see how much it took to move each robot. -Taylor

Spin Test


The Spin Test tested how fast the robot could spin 360 degrees.
  • The drive field used standard FTC field tiles.
  • Total robot amps were recorded for each run.
  • Time to spin 360 degrees was recorded for each run.
  • At least 4 testes were recorded for consistent results
  • The robot was weighted for the base weight
  • 10, 20, 30 and 40 pounds were added to the robot for each run

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We timed and tested the amperage of the bot as it spun around at different weights-Samuel

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The holonomic drivetrain did exceptionally well during the spin test. -Matthew

Ramp Test


The Ramp Test tested if the robot could climb the ramp.
  • The drive field used standard FTC field tiles.
  • The ramp was a standard FTC ramp from the Cascade Effect Game.
  • Pass/Fail if the robot could drive up he ramp
  • The robot was weighted for the base weight
  • 10, 20, 30 and 40 pounds were added to the robot for each run

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We tested if the robot could make it up the ramp with this drivetrain at different weights-Samuel

Science/Engineering


Robot speed


Wheel Diameter X Pi X Motor speed = Inch/min

4" X 3.14 X 150 = 1884 inch's/ min or / 60 = 31.4 inch's / sec
3" X 3.14 X 150 = 1413 inch's/min or / 60 = 23.5 inch's/sec
Tested Distance = 192 inch's

192/31.4 = 6.1 seconds theoretical time to run course with 4" wheels.
192/23.5 = 8.1 seconds theoretical time to run course with 3" wheels

Most robots at minimum weight tested faster predicted speed.


Conclusions


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As you can see in the above graphs, TWA-1 performs very well. TWA-1 consistently functioned well with weight up to 40 pounds.~Melea


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All of the robots other than the holonomic drive drew acceptable amperage.
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The holonomic drive and the four wheel plus Omni are not competitive as defensive robots and will be easily pushed around by other robots. The tread robot's data is high but proportional when compared to other designs because of the wheel size difference. The TWA-1 performs well and consistently in this test, proving its potential as a defensive robot.~ Melea


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The high performance wheels draw more current, but can also pull more weight than other wheel combinations


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The TWA-1 performed spectacularly without fail in this test. The 10 wheel drive was nearly un-pushable. Please note the weight added to the system because some robots do not perform well with a robot this heavy.~Melea



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This is arguably the most important test; on the playing field, agility is key to competing in the game effectively. As you can see the TWA-1 performs superiorly in this test.~
Melea

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The four wheel drive systems used more amps than are practical. Drawing this many amps will drain a battery very quickly.


Advantages and disadvantages of each drivetrain:


2 Drive wheels, 2 Motors with 2 Omni Wheels

+ Easy to design
+ Easy to build
+ Light weight
+ Inexpensive
+ Long battery life

- Maneuverability
- Underpowered drivetrain
- Will not do well on ramps
- Less able to hold position
- Not effective for defense
- Not able to support much weight and move effectively

4 Drive wheels, 4 Motors - Not Connected

+ Easy to design
+ Easy to build
+ Light weight
+ Inexpensive
+ Long battery life
+ Able to hold position
= Does decently on ramps
= Decent maneuverability
- Not utilizing full potential out of all the motors because they are not connected
- Not effective for defense
- Not able to support much weight and move effectively

4 Drive wheels, 4 Motors - Connected

+ Relatively easy to design
+ Relatively easy to build
+ Light weight
+ Able to holding position
+ Does well on ramps
+ Utilizes full potential out of all the motors because they are connected
= Inexpensive (note: chain and sprockets do not come in the Tetrix kit)
= Decent Maneuverability
= Battery life depends on weight
= Effective for defense
- Not able to support much weight and move effectively

10 Drive wheels, 4 Motor - Connected

++ Best at holding position

+ Does well on ramps
+ Utilizes full potential out of all the motors because they are connected
+ Very effective for defense
+ Supports obese robot well
= Decent Maneuverability
= Weight neutral
- Short battery life
- Difficult to design
- Difficult to build
- Expensive

6 Drive wheels, 4 Motor - Connected with 4 Omni Wheels

++ Maneuverability: spins on axis well
+ Great at holding position
+ Does well on ramps
+ Utilizes full potential out of all the motors because they are connected
+ Very effective for defense
+ Supports obese robot well
+ Excellent battery life
+ Will support high gear ratio
= Weight neutral
- Difficult to design
- Difficult to build
- Very expensive

Track Drive, 4 Motors - Connected
+ Easy to design
+ Easy to build
+ Light weight
+ Long battery life
+ Able to hold position
= Does decently on ramps with track treads
= Decent Maneuverability
= Effective for defense
= Cost neutral
- Inconsistent turns make autonomous extremely difficult
- Drive train needs to be geared up to reach competitive speed
- Vulnerable, needs to be protected

Holonomic, 4 Motors - Not Connected

+ Long battery life
+ Inexpensive
+ High Maneuverability
= Moderate weight
- Hard to design
- Hard to build
- Extremely difficult program
- Not able to hold position
- Slow- Cannot go up a ramp
- Not at all effective for defense

TWA-1

++ Maneuverability: spins on axis well
++ Supports robust robot well
++ Great at holding position
++ Very Fast but controllable
+ Does well on ramps
+ Utilizes full potential out of all the motors
+ Very effective for defense
+ Will support high gear ratio
= Weight neutral
= Build moderate with instructions
= Moderate battery life
- Expensive



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