Accumulator Update!

My primary work on the Engineering 89/90 team responsible for the electric powertrain of the 2016 DFR car has been on the accumulator — the electrical energy storage device for the vehicle.  I’ve spent a lot of time looking for the right battery cell.  Even though I had prior experience with battery cells, it’s been a very difficult task!  Balancing the energy density with the power density of a cell demands a keen understanding of the overall strategy for the electric powertrain…are we willing to accept more weight in order to gain more power output from the accumulator?  Design risks (i.e., risks to functionality and timeline) are were a major factor in the battery pack design.  How difficult is it to weld together many small cylindrical cells?  How can we circumvent the significant design challenge that is building a battery pack with mechanically unprotected pouch cells?  All these considerations, in conjunction with the significant challenge of sourcing viable lithium ion cells from non-OEM suppliers, slowed the process of cell selection (and battery architecture choice), but then, just in the nick of time, we found a prismatic li-ion cell that is perfect for our car!

The cell we’ve chosen is highly power-dense and reasonably energy dense (extremely energy dense in comparison to other prismatic cells, at 104 Wh/kg) and comes from a Florida supplier called Lithionics.  We are extremely excited by the level of safety and stability (especially when we are talking about lithium ion chemistry) that the cell affords us.  That high level of safety is right in line with the “professionally constructed” component of our team’s 2016 vision.  The cells are en route and pack design iterations are underway, and right after Christmas, the mad rush to construct the battery pack will begin!  Wish us luck, because without a battery, we cannot store the electricity we need to spin our motor and drive this car (hopefully down Victory Lane come May 2016).

Ben Parker ’16
Primary Accumulator Designer

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Control Freaks

Hi There,

Embedded Hybrid Controller team here! We’ve been having a blast configuring the main controller for the car, messing around with data communication, and learning about Simulink.

Just so you know this year we’re building a parallel hybrid where the motor and internal combustion engine (ICE) drive the rear axle. This has led us down a long and windy path of torque splitting, torque vs. speed control, and other hybrid vehicle control algorithms. We’re still diggin into it but here’s a quick view of our initial attempt at simulating the powertrain:

simulink_model_overview

This is a top level diagram and we’re working at getting all the different components such as the engine and motor working in unison. We have a mentor at MathWorks that is teaching us to use Simulink and model hybrid vehicles. Shout out to Wit! Thanks!

On the hardware front we have made considerable process! By that I mean all the hardware is chosen and working! We’ve got a very fancy oscilloscope that can decode CAN messages to help us debug and we’re using an Arduino Mega with a CAN-BUS and RS-485 shield to transmit CAN messages from the motor controller, engine control unit (ECU), and battery management system (BMS) to our controller. So far we are not hooked up to the actual components but we are testing our hardware by generating CAN signals from the scope and sending those out. The controller itself is from SunEdison and has a Freescale iMX286 processor and can act as a Wi-Fi host. Here’s a few pictures to make this description a little more clear

Our very fancy, touchscreen, oscilloscope that can decode CAN messages
Our very fancy, touchscreen, oscilloscope that can generate and decode CAN messages
PCAN adapter (replaced by RS-485 shield), Arduino with CAN-BUS shield
PCAN adapter (replaced by RS-485 shield), Arduino with CAN-BUS shield
Connection to the console port on the controller
Connection to the console port on the controller
CAN signals generated by the scope received by the controller!
CAN signals generated by the scope received by the controller!

So we do have communication between devices that send CAN messages (ECU, motor controller, and BMS in theory) and the controller, but what good is data if you can’t share it!?

Part of our project is to display data (engine RPM, engine temperature, battery state of charge, etc.) in real time to help diagnose performance issues. To do this we will activate the controller as a Wi-Fi host and display the data on a web app we are building. This is to be developed in the winter, for right now we’re a bit tied up with creating and validating test procedures for the hardware.

We’ve done a lot of work but there is a lot more to do! We’ll update you again soon!

Hello!

Hello Everyone!

This is our new blog and we hope you enjoy it! We started it a little late but I’ll attempt to catch you all up! So far we have:

  • Developed a detailed project plan to keep us on track for the rest of the year
  • Re-designed the back half of our chassis in SolidWorks
  • Began to modify the rear half of the chassis
  • Gone roller skating together
  • Ordered a motor, motor controller, batteries, and started working with our Battery Management System (BMS)
  • Bought, rode, and disassembled a KTM dirtbike currently sitting in our lab
  • Planned out our electrical system and started working on PCB’s
  • Designed an impact attenuator
  • Nailed down the hardware for our control system
  • Created a rough Simulink model of our vehicle
  • Spent many a Friday and Saturday night in Thayer
  • Cleaned and organized our lab!
  • Raised funds for the team (and no intention to stop now!)
  • Talked to lots of different people about cars, hybrids, and the like
  • Learned more than can be expressed in words from said conversations

So that’s the idea! There are of course little things here and there but that’s the bulk of it. This week we filled out our Electrical Systems Form and we have our mentors from General Motors coming out to the Granite State for a design review! This weekend we are giving a presentation for the First Lego League here at Thayer! Stay tuned for photos, videos, and more about all these wonderful things!