Duke University Motorsports is a student group that designs and builds open wheel, single seat race cars to compete in the Formula SAE competition sponsored by the Society of Automotive Engineers. The team consists of Duke students from both Pratt and Trinity, in all classes. The purpose of the team is to provide students with a way to gain practical design and manufacturing experience in a fun and challenging setting.
Although we had a great PCB design for our EGT Amplifier that has been reliable, I made some layout changes that would make the final SMT soldering much easier. Instead of the double sided board previously built, the new layout is now all on one side so the whole board can be SMT soldered in one go. The header holes were also made larger so that the wire we use can properly fit through the holes. Last year we had to cut the wire diameter in more than half and that led to a very poorly soldered connection. The header holes on the Fan Controller were made larger as well. I just got the boards from OSH Park and they look great!!
The updated design for the EGT Amplifier board that is one sided and has larger header holes
Click below to see more pictures of the PCBs and stencils...
So we've had a lot happen since our last blogpost. We will be posting a lot more frequently about the teams progress, so expect weekly to biweekly updates!
That being said, our current design has changed quite a bit from what we had in the summer as some of our design goals had to be pushed back a year. The first objective was for us to build the frame. This year we decided to weld the frame ourselves (props to our master welder Costi Shami). After designing the frame exactly how we wanted in CAD, I used VR3 Engineering - Cartesian Tube Profiling to manufacture a laser cut kit with all the tubes that make up the frame. This made assembling and welding the frame so much easier. Even the camber block points were laser cut! We'd like to thank VR3 Engineering for a fantastic frame tube kit!
Cost has been hard at work welding away and we are almost done with the frame! Here is a photo of Costi and the frame from a few weeks ago:
Earlier this summer, I did a lap time simulation study earlier this summer to understand the sensitivity of lap time on a number of parameters (including mass, power, downforce, drag, and mechanical grip). The results of the lap simulation showed mechanical grip to be the most important parameter, followed by downforce and then mass. Since there is a limit as to what can be achieved with mechanical grip, past those limits aero is still the biggest enabler for decreasing lap times.
After about 3 weeks, we have a basic vehicle architecture for 2014. This has been a pretty intense period, as three weeks ago the car was a blank assembly.
10 inch wheels - affects packaging for WHUBs, suspension, and frame primarily
Narrower track (~46", front and rear)
Smaller wheelbase (60")
Complete frame redesign - no rear box
Lower occupant positioning - CG focused
Lots of downforce
Once again, the focus will be on mass, aero, and mechanical grip. All of these need to be understood on at least a high level to design an architecture, as many of these enablers and decisions will drive packaging. For example, originally I started with a rear box because I thought diffuser design would dictat my suspension points, but with CFD I've found that I can actually get better downforce with a shorter diffuser (more on why that is in another post).
So let's take a walk through how to set up an architecture:
I must say that I still haven't full recovered from the tornado that was the month prior to competition, which is why I haven't had the opportunity to update the blog. However, we did take a lot of pictures of the design and fabrication processes, so I would like to go through all of the progress we made as a team building our car, named OD-13.
Just a quick note: I apologize for any redundancy regarding the pics that may occur...I just want to make sure I cover everything, because there is a large gap in the blog.
The great thing about a brand new design is the design latitude. The bad thing about a brand new design is... the design latitude. Making everything fit properly is never an easy task, and often requires you to take a step back and look for some very creative options.
With the help of susprog, I think I've finished the first iteration of the suspension packaging.
The front was relatively easy - I was able to get the motion ratios required and the ARB packaging with pullrods without too much issue.
The rear on the other hand is much more difficult because of the addition of a driveshaft, frame limitations, aero limitations, and rim clearance. However, everything fits, the min clearance at static is slightly less than 0.1" (cutting it close, I know), so a lot of the success of this design relies on good tolerances and properly jigging parts during construction.
Design is moving along at lightning pace right now, with the whole team contributing now. With lapsim analysis we've been able to figure out what to focus on for this year - the main goals are (in order) to 1) improve grip, 2) improve aero, and 3) reduce mass. We might be shooting for a narrower width as well due to the nature of the Michigan course, but not sure if a narrower track is worth the reduction in aero area.
A lot of goals 1 and 3 will be accomplished via the 10" Hoosier LC0's (we think - tire data analysis is currently ongoing to verify). Also, we're looking for significant reduction in CG via driver positioning and packaging optimization. Weight reduction is looking for a lot of creative design, better analysis to enable less over-design, better CAD accounting for mass, and better manufacturing methods. CFD analysis has just started today to optimize the aero package for this car, so there's lots of work to do still on that front.
Some teaser shots of what the car might look like next year:
I would just like to say congratulations to the team for placing 24th this year at Michigan. A lot of hard work went into this year, and it certainly wasn't an easy competition, but the team got it done.