1. The Journey to a West Coast Drivetrain
Thomas Herring,
Nicholas Oprescu-Havriliuc,
Charlie Fisher
Good afternoon everybody.
We are from Team 610 and today we would like to share with you our journey to complete a West Coast Drivetrain.
This project has been done by Thomas, Nicholas and Charlie.
Thomas is a senior in our Robotic team and he is the executive of design and manufacturing. He has several years of building and competing experience.
Nicholas and Charlie have joined the Robotic team in 2015 and worked in the programming and design sections of the team. Last year Nicholas was also the operator during the competition season.

2. Summary Project Scope Drivetrain Types Overview
What is the West Coast Drivetrain?
Approach
Engineering Decisions – Summary
Building the perfect West Coast drivetrain
Chassis
Gearbox and CIM
Chain and Sprocket Selection
Traction Wheels
Project Phases – Summary
Project Plan/Schedule
Design Sketches
Computer Assisted Design
Building
Final Product
Lessons Learned
Today we will take you through our journey from the moment when we were asked to design a new drivetrain to the completion of the project.
We will introduce to you some different type of drivetrains, give you an overview of our engineering decisions such as gearbox, drivetrain, etc. and ultimately share with you the phases we went through with the development of this project.
We will conclude by sharing with you some lessons learned from this project.

3. Project Scope
Scope:
Prototype a West Coast drivetrain system for future applications
Why:
First attempt of Team 610 to build this drivetrain
Timeline:
Design, build, and prototype before the build season
At the end of the 2015 competition season our mentors challenged us with building a drivetrain for future applications.
We decided to build the West Coast Drivetrain. This type of drivetrain has never been built by our team and therefore making it great challenge.
We were given this tasks with the purpose of coming forward with a drivetrain before the build season.

4. Drivetrain Types Overview
Tank Drive train
Left and right wheels are driven independently. Easy to drive, design, and build
West Coast Drive train
Uses wheels on the exterior of the chassis, attached to bearing blocks
Omni-Directional Drive train
Wheels modules rotate on the vertical axis to control direction
Swerve/Crab
Slide
Mecanum
Holonomic
There are numerous types of drivetrains that can be used in different applications.
Each have certain advantages and disadvantages and depending on the scope of your robot or the rules of the games for that year you can choose to use one or the other.
Tank Drive train has been used in numerous 610 applications.
West Coast Drive train is the scope of this project.
Omni-Directional Drive train has several variations as described here.
Tank Drive 

5. What is the West Coast Drivetrain?
Definition: A style of drivetrain that originated in California that emphasizes light weight, serviceability and reliability. This is accomplished with cantilevered wheels mounted to the frame with bearing blocks and a gearbox directly coupled to the central wheel .
Pros
Live axle middle wheel cannot lose power
Reduced weight (no side bars)
Maximize the width of the wheel base
Ease of maintenance (cantilevered wheels)
Easy to change gears, wheels, sprockets
Easy to adjust the chain (for required tension)
Cons
Sensitive to lateral impact
Wheels are unprotected
Requires higher precision machining
Bumper mounts more difficult
Read the definition…
A team may chose this type of drivetrain if they want a light weight, adjustable chain (for easy maintenance), ease of gear, wheel, and sprocket change. Ultimately as an advantage it is important to note that the power is sent directly to the wheels.
The team has to be aware of certain limitations such as protection of the wheels and an increased difficulty to mount bumpers. Since the power is transmitted directed to the wheel, higher precision is requiring when mounting the CIMs, gearbox's, and wheels.

6. Approach Research Previous drivetrains developed by Team 610
Design manual by Ryan Tam (Team 610)
Competition observations from 2015 season
Published Simbotics drivetrain examples
High Level Requirements
Deliver speed and provide strength
Easy maintenance to moving parts
Develop a brand new drivetrain
Once we had the scope of the project determined: West Coast Drivetrain we started our research. As you can see we went back to our 610 extensive documentation of various drivetrains. We also benefited from an excellent design manual put together by one of our own Alumni – Ryan Tam. I honestly will tell you that this design manual was for us of maximum importance.
We (Charlie and I), the rookies, benefited extremely from an excellent 2015 build and competition season. The regionals and the St Louis competition gave us an excellent opportunity to see strengths and limitations in some robots that we competed against. Some of the lessons learned form the season where incorporated in this design. One of them was to design a drivetrain that can be easily fixed in the condition of competition. You can make an analogy to the Formula 1 tire changing that occurs in few seconds. I am not saying that we can change our wheels in 20 seconds, however, we want to create something that can be fixed quickly if required.
Our requirements were very clear. At all times we challenges ourselves to make sure that whatever we design can be traced to these three requirements: speed and strength, ease of maintenance, and acquire new skills by building a new type of drivetrain.
Throughout the design we adopted an iterative approach in designing the drivetrain. We advised with our senior team members and our mentors. We discussed the engineering options and selected the most suitable one. Also, very important in everything that you do is to established a project plan with key milestones that you have to meet. Make sure that they are logical and reasonable.
Approach
Review multiple designs of West Coast
Discuss them in the team with the seniors and mentors
Develop Engineering solutions
Develop and plan the Project Phases

7. Engineering Decisions - Summary
Chassis
Gearbox and CIM
Chain and Sprocket
Traction Wheels
Now, we will take you to the journey of describing what were our engineering approaches for each of the components.
For each of these categories that you see on the slide we chose to present to you two things.
First some general knowledge information which we think is relevant and which we had to understand to make a choice.
Second some specific design choices that we adopted for our drivetrain.
Now, let’s dive into the first summary item – CHASSIS

8. Building the perfect West Coast drivetrain Chassis
Wheel base is maximized
Wheels are over hung
More space inside
Light weight
Requires higher precision machining
Major decisions:
Used rod through rectangular channels instead of gussets for strength
Used aluminum rectangular channel
As general considerations for the chassis, as we have already spoke about, this drivetrain solution maximizes the size of the footprint. It is light and required precision when you mount the CIM and engage the wheel directly via the gearbox.
For our solution we used aluminum with a rectangular profile. Our chassis is basically a square with six wheels and with the two CIMs powering the middle wheels (see pic 1)
For our solution we recognized immediately that we need to strengthen the chassis by using some rods to keep the sides very firmly together (see pic 2). You may be asking why we did not use gussets. The answer is that the gussets would interfere with the bearing blocks.
Now, let’s dive into the next summary item – the gearbox and the CIMs >>> flip page
<< Pic 1 - Actual Chassis
Pic 2 – Rods for strength >>

9. Building the perfect West Coast drivetrain Gearbox and CIM
Fast? Slow? Both?
Select the appropriate gear for optimum speed and torque.
Determine the number of CIMs to power the wheels
How many speeds you should have?
One single speed gearbox, typically 8-12 ft/s
Two speed gearbox, typically 6-18 ft/s
Major decisions:
Use three 2.5 CIM motor for each gearbox (two)
Used one single speed gearbox with two stages
First reduction is 12:60
Second reduction is 30:48
Gear ratio for the right strength and speed is 8:1
As general consideration for the gearbox, it is important to balance speed and torque.
If you gear your robot to high
You will not have enough torque to move
It is hard to control when you move
If you gear your robot too low
You will have too much torque and your wheels will slip before you reach max power
You will be too slow to be effective
Also it is important to select how many speeds you should have. As a general rule of thumb more speed means more speed however it means more weight.
For our solution, we chose to use three CIMs and a single speed gearbox with two stages. We could not reduce the speed on one stage hence we went first for a reduction of 12:60 the then with the second stage we further reduced it 30:48. The optimal ration of 8:1 as thus obtained for the appropriate strength and speed.
Now, let’s dive into the next summary item – the Chain and Sprocket selection >>> flip page
Pic 1 - Actual Gearbox >>

10. Building the perfect West Coast drivetrain Chain and Sprocket Selection
Chains
Multiple standards are available
Distance between the wheels should be a multiple of chain pitch
Sprockets
Largely affects the amount of tension in the chain
To minimize tension, use the largest sprocket that provides enough clearance
Major decisions:
Used one standard size chain #25
Used #25 22 teeth hub sprocket 0.5 hex
As a general consideration for Chains there are several standards available and you have to balance the size for strength and size. Sprockets are also coming in different sizes and your selection has to be based on what can be fit for the space that you have available.
For our solution we used the standard chain #25 and a sprocket with 22 teeth.
Now, let’s dive into the next summary item – the Bearing block >>> flip page
Pic 1 - Actual Sprocket >>

11. Building the perfect West Coast drivetrain Bearing Block
Bearing blocks clamp onto the rectangular frame
They are meant to adjust the chain tension
Wheel on the outside and sprocket on the inside
Major decisions:
Custom designed bearing block
Used two inch plates
Plates are inches apart
<<< Pic 1 - Actual Bearing Block
What is special about the west coast drive is that it uses bearing blocks. Bearing blocks are there so that it is possible to provide adjustment to the tension of the chain if needed. Our bearing block is custom designed, meaning that we did not buy it off the shelfs, we designed it ourselves. The left picture is our bearing block and the right picture is the off the shelf bearing block. The shaft you see is where the wheel would be mounted (on the outside of the drivetrain). On the inside of the drivetrain is where the sprocket would be placed. The sprocket is connected to the chain.
Now, let’s dive into the next summary item – the Wheels >>> flip page
Pic 2 Off the shelf bearing block >>>

12. Building the perfect West Coast drivetrain Traction Wheels
Wheels Types
Traction Wheels: Standard wheels with varying amounts of traction, strength & weight.
Kit of Parts Wheels
AM Plaction Wheels
Pneumatic Wheels
Colson Performa Wheels
Size: Small wheels require less gear reduction, and provide lower center of gravity
Major decisions:
Used Colson Performa 4 inch hex bore wheels for good durability and traction
Used six wheels drivetrain
There is a large selection of traction wheels that you can choose from and they have to be appropriate for your drivetrain. You have to take into consideration the weight and size of your drivetrain, the mobility and movement types that you are planning for your drivetrain, the traction required, and of course their size relative to the robot size.
For our solution we have chosen Colson Performa (see Pic 1) because they are light weight, have quite grippy tread. We have chosen 4 inch hex bore wheels given the size of the drivetrain. Keep in mind that for a larger drive train they may not be suitable. As you saw with our chassis we chose six Colson Performa wheels.
With the wheels presentation we have finished the overview of the engineering solutions. Now is time to move on to the project phases summary. >>> flip the page
Pic 1 - Actual Wheel >>

13. Project Phases - Summary
Project Plan
Design Sketches
Computer Aided Design
Building
Now, let’s talk a bit about how our project came to life and the phases it went through to get to the end result.
At the beginning of the summer of 2015 we put together a plan to develop this drivetrain. We started by sketching several ideas and brainstormed what engineering decisions we needed to make. Then we started to develop the drivetrain using Solidworks. The development of the drivetrain went through multiple iterations within our team. It was a tremendous learning experience and this is how it went. >>> flip the page

14. Project Plan/Schedule
Sketches
CAD-ing
Review CAD-ing
Start of project
May 2015
Present sketches
May
Complete CAD
Sep
Review CAD
Sep
Manufacturing
On the project schedule this is how it unfolded.
Just before the end of the school year we reviewed the sketches of the drivetrain. We made some choices and initiated the CAD design.
Over the summer we continued the CAD. As you can imagine all of us had vacation plan and we worked through our vacation plans.
When the new school year started we pulled the team back and reviewed the design and made some final adjustments to the design.
Now, let’s walk through some of phases that we undertook: sketches, design, CAD, >>> flip the page
Complete Manufacturing
Nov

15. Design Sketches Used drawing notebook, pencils and erasers
Brainstorm ideas on what we need to consider
Sketch the drivetrain side and front
Sketch the chain placement, and gearbox
Pic 1 – Design Sketches >>
Major aspects discussed:
Transmission Options:
Engage all three wheels directly
Engage two wheels and have the third following
Engage the middle wheel and have two following
Strengthen the frame using metal rods
The beginning of our project started with some good old sketches on a drawing notebook, pencils and erasers.
This was the best start for brainstorming ideas and review options.
The initial drawings showed the drivetrain form side and front.
We discussed and sketched the gear and the appropriate ratio.
We also discussed about the options we can use to engage the wheels that are driven from the motor. There are three transmission options that we reviewed as you can see here on the slide. In the end we chose to engage the middle wheel and have the other two wheels following.
At this time we also thought how is best to strengthen the frame of the chassis, and from the teams past experience we selected to strengthen the frame by using metal rods.
Now is time to look at the CAD design phase. >>> flip the page

16. Computer Assisted Design
Used Solid Works
Develop the design through an iterative approach
Develop the frame
Develop the gearbox
Add the wheels axles
Add the transmission chain
Add the wheels
We used Solidworks to design the drivetrain. The work has been done either remotely or in the school lab.
The work has been done by Nicholas and Charlie then reviewed by Thomas in iterations.
First, was to develop the chassis frame
Second, we attached the CIMs and the gearbox;
Third, we introduced the rods to strengthen the structure
Fourth, we added the wheels axles; we incorporated the Sprockets and the transmission chain
Finally we attached the wheels
Pic 1 – CAD Design >>

17. Building
Not in scope for this project

18. Final Product

19. Lessons Learned CAD experience was limited to one year
Learning of the technical terms
Its hard to meet during the summer (team and mentors)

20. Thank You