Saturday, February 13, 2016

Battery Update: Front and Rear Pack Arrangement

 After a long week of CADding and designing, Joey managed to generate a design for the front and rear packs of our car thanks to input from the meeting of the minds we had last week. In total this pack will be 58s64p distributed between the front and rear of the car, giving us a roughly 72kWh pack! The team had an internal design review this past Saturday with Prof. Dan Frey to look over everything, see if any considerations were left out, and generate ideas about wiring and assembly of the packs.

Tuesday we had a design review with our battery providers Boston Power. The meeting went well, and they provided us with even more ideas to consider including crashworthiness, cooling, wiring, and weatherproofing. 

Saturday, February 6, 2016

This week in EVT EE

(note: this post was written by a new member without a sense of humor)

Preparations to command someone else's magical metal box to use electrons from large energy boxes to spin something.

caption: magical metal box; alt-text: Sevcon motor coftroller
{caption: Magical metal box's life support system; alt-text: 12-volt power supply}
{caption: a smaller version of our large energy boxes; alt-text: The real ones are much nicer, I'm told}
{caption: DC and smaller than what we are using, but it still spins right?; alt-text: The real motor is AC and much larger}
Some little metal strings go between our squirrel containment facilities and the giant metal box to allow the magical squirrel inhabitants to talk to each other.
{caption: metal strings; alt-text: wires}
{caption: squirrel containment facility; alt-text: our devboards at work}
The metal box really wants to talk to someone, but our squirrels were deemed too unimportant because they don't know the secret password.

To learn about the metal box, we needed to stare at lines formed by small squares on a glowing rectangle.
Once we decided that the lines failed to contain the information we needed, we pressed large buttons repeatable to create our own lines for another human to interpret.
That human, a person that works with the creators of the magical metal box, will give us the secret password that their squirrels require.

More clear explanation:
This week, we worked with the Sevcon Gen4Size10 motor controller.
It sits on a table with power supplies rather than the actual batteries for testing.
After working for a while to learn how to use CANopen, and reading through the documentation for the motor controller, we began trying to talk to it using our devboards.
We found that the motor controller is in master mode, and tries to send out a SYNC message to tell the other CANopen nodes to talk to it.
After trying to write values to the motor controller to change it's ID, disable the SYNC message, and switch it to slave mode, we found that it was always broadcasting an error message with each attempt.
The error message pointed us to another CANopen index to read, which informed us that we do not have a high enough access level.
In order to change the access level, a password must be provided to the Sevcon.
We have sent an email to a representative at Sevcon asking about the password.

MechE Battery Party!

MechE Updates

Our primary concern today was designing structures to hold and support our battery packs in the back of the Opel. By the afternoon, literally everyone on the MechE team was engrossed in this task. We were even honored to have Sir Nicholas Arango from the EE team come and help us generate ideas.
Being a team with a small car and big ambitions, one of our biggest design constraints in our Opel project is that we have 464 individual battery packs to distribute between what used to be the engine compartment and the space which used to house the back subframe and gas tank. Each group of cells has to be housed such that none of the cells are at risk of being ruptured in the case of a collision. At the same time, the front and back compartments each require a cooling system for these cells, and in addition to our subframe, motor, and transmission in the rear compartment, each compartment will eventually house one or more modules such as our motor controller or our battery controller. Our design constraints, therefore, are difficult to work with, and it took hours narrowing down what path we should take.

Alex helping lead discussion. Alex and Joey, who had done a great deal of work designing our battery supports in weeks past, proved invaluable.

Leave it to Rango to bring out the best in people.

After hours of work, first in small subteams and then as a whole, we were able to come up with a modular design for our supports which could be implemented universally across virtually any permutation of battery placement. We designated two teams—one to generate plausible battery placements with batteries oriented towards the back of the vehicle, another with cells toward the passenger side—to create a library of battery placements to choose from. This coming week, we will select the design that seems most feasible, stable, and space-conscious so we can start building the support frame itself.

A set of one of many sizes of battery module CADded by Joey
In addition to this, Jacob, Ryan, and Olivia worked with Jimmy from the EE team to decide how and where to mount potentiometers to the accelerator and brake pedals in the Opel, and Joey created comprehensive CAD of the structural members of the Opel frame.

Joey’s CAD of the structural components of the Opel frame