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.

Sunday, March 11, 2012

Spring break and NCCAR update

We headed out to the North Carolina Center for Automotive Research on Thursday and Friday to do an initial shakedown and track testing.  After a long and tiring spring break, we got the car to the point of being ready to drive just in time for our planned NCCAR test date.

Car with aero!  The rear wing is the old one from last year.
I would like to give a huge thanks to Simon and Sam at NCCAR for allowing us to use their facilities at a highly discounted rate.  NCCAR has amazing facilities, and we hope that they'll continue to support our program in the future!

While we were there, of course we found problems, but hey, that's what testing is for.  Details on spring break and NCCAR after the break...

Let me just first start off by saying how awesome spring break was.  What we were able to accomplish over break really embodies what Duke motorsports is about - a group of hard working, dedicated people willing to do whatever it takes to make this car happen.  Of the six of us around for break, everyone gave 100%.

Day 1 (Saturday, the day of the UNC-Duke game): Not too much happened today because of the game.  Me and Danny went up to the shop before the game and got the seat mount tabs and pedals machined.  Unfortunately, one of the drawings may have been wrong, and two of the holes didn't line up on the pedals, and the machine shop was closed by that point.  I would also find out tomorrow that 3 of the 4 seat mount tabs didn't line up with the holes in the seat, so back to the machine shop on Monday...

We also popped the seat out of the mold.  Man, that was difficult.  Lots of water (to dissolve the PVA), lots of air, lots of force, and lots of razor blades and prying.  It did eventually pop out though.
Seat popped out of the mold
A few spots were a bit dry on epoxy, so we also slathered a bit more Hysol on the dry parts.

Day 2 (Sunday): The real work starts today.  Costi added another layer of carbon fiber to the intake to reinforce it, we set the front wing mounts in carbon fiber, and I cut the front wing to fit the frame.
Cutting the big part of the front wing to fit the frame.  Cuts nicely using the cut-off wheel.
Meanwhile, Matt, JP, and Danny were upstairs putting down carbon fiber on the rear wing sections.  We did not end up using the new rear wing this week, but most of the hard work is now done on the rear wing and it just needs to be put together now.

We also finished the diffuser mounting.  The elevator bolts were epoxied into the diffuser as the hard mounts, and nuts were welded onto the tabs to make it easy to attach and remove.  We did hit a small snag in the mounting, where the middle tabs ended up being pretty much inaccessible due to their placement right under the fuel tank, so we welded nuts onto those tabs and took a couple of elevator bolts and ground a groove for the Dzus tool so that it could be screwed in from below.  Works great, and everything aligned properly the first try (much to my surprise).
Diffuser mounted

Day 3 (Monday): Danny and JP went to the machine shop to finish the hubs (the clearance for the knurls on the studs had to be machined in), pedals, and seat mount plates.  We also received the mill control unit that broke later that day, and so we got the mill working again.  Took a bit of fiddling to set the backlash, but we checked everything out and it looked fine.  We were able to machine the rear spindles for the press fit into the hub that night as a result.

We were able to get the seat mounted by Monday night for the most part, as well as the headrest tacked into place.  However, the welding was not easy because of awkward angles and minimal clearance, so I wasn't able to finish welding on Monday.

Day 4 (Tuesday): I came in early and with a clear head, was able to finish welding the seat mounts and headrest.  Me and Matt also laid up the endplates for the front wing so that we could finish the front wing the next day.
Front wing plates in vacuum bag
Me and Costi also got the radiator mounted, with the diffuser now in so that we could check clearances.  Turns out it fits nicely as shown below:
Sorry for the blurry picture...
Day 5 (Wednesday): Mostly putting finishing touches on the car.  At this point pretty much everything was ready to go (or so we thought).  We put in the clutch and throttle cables, John finished the electrics required to run and put in the DAQ system.  We also had to go pick up gas, get the last tire mounted on the rim (Discount Tire in South Square is awesome and gives us a special rate), pick up the truck, trailer, and load everything.

Costi welded up the links for the rear wing mounts (temporary ones for now - the final ones will be carbon fiber), I welded on the tabs for the front and rear wings, and Costi, Danny, and Matt also finished laying up the front wing.  We let it set overnight so that it would be ready to go for Thursday.
At this point things started going wrong.  We started up the engine (eventually, after some weird communications issues with the ECU), and spun the wheels in the air only to find some pretty bad drivetrain movement.  We attributed this movement to misalignment of the drivetrain, so me and JP stayed through the night to get it fixed.
A very tired JP working on the drivetrain
We took it all apart, played with the shims, figured out which combinations of shims aligned the drivetrain the best, repressed one of the bearings, bolted everything back together, set the chain tension, and so we were ready to go.  It was about 5am at this point, so we went back and caught a couple hours of sleep before leaving for NCCAR the next morning.

Day 6 (Thursday): We met up bright and early at the garage, got the car into the trailer, and headed off.  We arrived at NCCAR at 11ish, unpacked, and got straight to work.  I set the alignment and corner weights (which amazingly were perfect and needed no adjustment at all).  At this point, the scales said the car weighed in at 432lb with half a tank of gas and no aero.  Not bad at all - much lighter than last year (we were closer to 450 with the same configuration last year).

A view of the garage from the upstairs area
We went for a quick drive.  First few minutes went okay, and then we heard the dreaded fuel starvation sound.  We checked gas, filled it up, pulled the master, and.. nothing.  Tried again, and nothing.  We checked power to the fuel pump, and it was fine, so we concluded that the fuel pump was dead.  That's what happens when you run it dry too many times...  JP and John ran out to Advance Auto Parts to pick up a new one.
The car Thursday afternoon
Meanwhile, Costi was complaining about the car skipping and hopping - so we took it back and took a look at it.  I looked at the front wheels and saw a lot of anti-ackermann... totally the opposite of the designed ackermann.  Then we turned the wheel and saw lots of pro-ackermann like expected.  Uh-oh, something was loose.  Turns out we forgot a nut on the steering arm attachment to the upright.  Oops.  Fixed that, but then we found the a-arm to be hitting the upright.  Oops again.  I set the bump stops to reduce the range of travel a bit, and we were good to go again.

Costi swapped in the new fuel pump, and we went out driving again.  By this point it was already 4:00, so we only had less than an hour left to drive.  I went out first this time, and it felt good, responsive, and cornered well.  I did a few full throttle pulls, and it was definitely strong.  Launched in first (all wheelspin), short-shifted into second (more wheelspin), and the thing just took off. 

Costi got in, started driving, and a little ways in, we hear a snap come from the car.  Uh oh.  The tripod had backed out of the half-shaft, and popped the retaining ring out.  A combination of too much play in the half-shaft, tripod housing that were a bit too short, and a relatively severe half-shaft angle cause the tripod to catch on the housing and rip itself out.

We got the car back to the garage, with a plan to get a new retaining ring and have the car ready to go again for the next day.  We ran around all over the place to find retaining rings that would fit, and while we didn't find any exact replacements, we did find rings that would work well (and as we would later find out, too well), since the grooves weren't very precisely machined.

After we got back, JP got to work on the drivetrain, and we all worked to get aero mounted.  The front wing (which weighs in at just under 7lb) took a bit of trimming to make fit, but eventually it went into place without much of an issue.  It is nice and strong (we put over 150lb on it just to make sure), and fits beautifully.
We got the diffuser in, mounted the old rear wing, and went to sleep.

Day 7 (Friday): It was a bit rainy in the morning, so we waited for the rain to stop before we went out to run.  Unfortunately, things didn't go so well, as the drivetrain grenaded again, this time a bit more catastrophically.  The same failure happened, with the tripod pushing itself out, only this time, since the retaining ring was stronger, the tripod stayed in and chewed up a pushrod, the tripod housing, and actually put enough force on the a-arm mounts to slightly deform one of the camber block frame mounts.  It also bent the bearing carriers.  Oops.

At this point, there was no way the car was running again without a major fix, so it was time to pack up and leave.  We will fix the drivetrain issue with a better toleranced half-shaft, new (deeper) tripod housings, and we will need to remachine bearing carriers to replace the broken ones.  Lessons were learned, but we will get this fixed and the car up and running again very soon.

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