25 July 2015 18:53

Pat's Corner: Design Error of the Month

Category: Competition

Hello again and welcome to FSG in less than a week.
As most regular readers know, I usually end the column with a 'Design Error of the Month'. Well, this month, the entire article is about a design error, a failure and the teams ability to recover.

I first met this Uni of Glasgow team when they competed in Class 2 at FS Russia in 2014, where they did quite well in presenting their new design. As previous UG cars had been, to be charitable, less than perfect, I kept a close eye on this better design and hoped the team would do well.

Their new car debuted last month at FSUK, where they suffered a catastrophic brake failure due to a design error in the brake discs.

 

I asked the team if I could use this as a future subject for 'DEOTM' without actually mentioning the team, but they disagreed. Not with publishing the error, but with remaining anonymous.

In fact, team member Yavor Gegov asked if he could write the story, so I am including it below. He account highlights all the good stuff about Formula Student.

I look forward to seeing you all next week. Make sure you join me for a coffee in Pat's Corner.

And remember, keep safe on your trip to Hockenheim. Red Bull is NOT a substitute for sleep!

Regards

 

Pat

Yavor Gagov's Letter

As with all FS teams UGRacing has experienced its share of ups and downs over the years. At the beginning of the 2015 season we once more found ourselves with a mostly new and inexperienced team. Hard lessons from previous years resulted in greatly increased knowledge transfer between generations but we still had a team with only three experienced members on board and our work cut out for us.

In 2014 the team spent far too much time attempting to attain perfection and due to a number of management issues ran out of time. Unfortunately the team failed to get the car on track for Formula Student 2014 at Silverstone and that miscalculation had placed us in a precarious position with our sponsors. They were keenly observing how things would develop during the 2015 season. 

To avoid these pitfalls in the new season a full 180 degree approach was taken, rushing everything out the door as quickly as possible, and of course going from one extreme to another is always guaranteed to work so well….

Two weeks before Silverstone the car was ready and was performing well. The team conducted as much testing as possible prior to the event and everyone was confident in the vehicle`s performance. Of course two weeks aren’t a huge amount of testing but it was weeks ahead of any car in recent memory.

With everybody happy UGRacing set off for Silverstone expecting a fairly smooth experience.

On the first day of scrutineering all things went well, save for a couple of bolts we forgot to drill for lock wire (huge thanks to TuDelft) and some foam padding we had missed out. Alas the endeavour still ended up taking all day and we were left to wrap things up on Friday. No problem we thought. 

On Friday we passed the technical and safety checks, and passed tilt in the morning with no significant leaks save from our driver`s nose which was quickly plugged. We continued over to noise but had to pull the car back in as our static presentations were due. These went well enough and as with the day before we thought all will be good and we`ll pass noise and brake on Saturday morning and off to dynamics.

Unfortunately for us this was a rather naïve way to look at it and arriving at noise bright and early we encountered the first major consequence of our rush everything out the door yesterday approach. 

The car was set up to idle rather high at 4k RPM due to a major vacuum leak in the plenum. This resulted in us failing the idle noise test and spending 6 hours trying to bring the idle down, sealing the plenum, and repacking the silencer. In the end the only way for us to pass was to plug the silencer and take the hit on engine performance. After a brief celebration we rolled the car over to the brake test, assuming that we had passed the major challenge to overcome this year. Smooth sailing from here on out, of course we were once more comically, tragically wrong…

We lined up the car for the brake test and our driver gave it a few goes. Three out of four wheels locked each time without issue. The rear left was acting up but we knew it was the new pads we put on that morning after discovering some oil had contaminated the old set.  As per the brake scrutineer’s advice we changed the bias a bit more to the rear and away we went.  The driver slammed on the brakes and as all four wheels locked a loud bang cut our jubilation in its infancy, our little world collapsed. The car spun out and our driver sat head in hands. 

Within seconds we were on the car and what we discovered left us shocked, our front left grey cast iron brake disk was shattered in about 5-6 pieces. Due to both budget and time constraints there were no spares and even if we had them, we had no idea what had caused this catastrophic failure of such a critical component. The disk was oversized and designed for a car a lot heavier than what we were running to account for any unexpected surprises down the line.

With most of the team despondent and ready to call it a day, the old team members having been in these situations before got to thinking. After some pondering we discovered that there was a combination of errors that led to the failure. 

The vent holes in the disk could have been positioned differently as to be further away from the edges and we could have been more careful with the amount of tabs we put on the chassis , which did add to a good weight increase on what we though the car should have been. 

But the main cause of these issues was a desire to do things quicker. The front callipers were mounted using a set of washers to ensure the disk was tracking centrally in the calliper. Tolerances in the brake mount were slightly off as the design was done from the calliper drawings before we had the actual units and it was one of those better be safe than sorry decisions that uncertainty gives birth to.

During the various testing phases these washers were in place however when the car was stripped and rebuilt for competition we had forgotten to put them back on. This lack of space on one side ate up the disk`s floating ability and under the repeated strain of locking the wheels of a slightly heavier car the lack of floating space caused the cast iron disks to go into bending. Massive failure was absolutely guaranteed.

Knowing what caused our problem allowed us to learn our lesson for next year however it was now Saturday, mid-competition, we were missing events and with sponsors looking on the stakes had been raised. Quite the high stress situation, I’m sure you’d agree.

Throughout the event we had had little issues here and there we got help from other teams and in the same FSAE spirit we helped others, giving parts to some, helping other pass noise with what we had learned etc. This spirit of camaraderie combined with the good rapport we had with the scrutineers gave hope to a number of team members that a solution could be found. After some running around TU Delft were willing to attempt machining new disks if we could find some material. Of course by this point cast iron was off the table and any sheet of 4mm thick mild steel plate was being systematically hunted for by team members scouring the pits. And even though we were in quite the pickle there was not one team regardless of how high tech a car they had that looked down on us or did not take our request seriously. People were diving into their storage spaces and trucks looking for anything that might help us.

Word quickly spread and people began coming down to see what was going on, either out of curiosity or to offer some sort of help or solution. Amongst these were two visitors to the event, sent over to us by NUST (who we helped with their exhaust). The guys that showed up had a start-up machining company in a borough north of London and since one of them was a former formula student competitor they had come up for the weekend to see the event. They must have liked our fighting spirit because they offered us to go with them to their shop and machine new disks overnight. An incredible offer that the team snapped up immediately. 

A plate of suitable thickness was found, the most valuable 4mm thick plate in the pits as three teams needed to split it. After some frantic cutting and a few boxes of plasma cutting disks later we jumped in a car and followed our newly found benefactors. 

Expecting to see a man in a shed type of operation our minds were blown when we walked into a pristine workspace dominated by the colossal DMG Mori DMU 75 Monoblock 5 axis CNC machine quietly humming in the corner.  The guys from Kazbro Ltd (www.kazbro-uk.com) proceeded to set everything up in a professional and efficient manner and at about midnight on Saturday the first cuts were made.

Sitting between operations we got talking with our new sponsors and were shocked to discover that they had been seeking to sponsor formula student teams in the London area for months but almost no one had replied to their emails. Of the teams that did, one had been offered the deal of deals - a full ride on unsprung machining with even the billets payed for by the company. Unfortunately this team had pulled out of the competition weeks prior leaving Kazbro sitting on various billets for hubs, uprights, and clevises. 

Needless to say we were there we were left speechless by the whole event. With quoting our disk designer “Stuff like this does not happen in the real world “ 

By the morning we were the happy owners of four new and improved brake disks. With a borrowed front calliper from Leicester and thanks to the incredibly supportive and understanding scrutineers we got set up to do the brake test at the very last possible moment and after a warm up run the car locked all four wheels. 

The team erupted in ecstatic jubilation and within minutes the car went out on track for endurance. Ensuring that UGRacing completed its objectives for the year, securing our sponsors and the team’s future.

We would like to use this article to express our deepest gratitude to all our sponsors who were so patient and understanding over the year and especially the guys from Kazbro Ltd who pulled us back from the brink. UGRacing hopes that our story will encourage others to maintain the great spirit of sportsmanship displayed by everyone, we would also like to thank, TuDelft, NUST, Leicester, Liverpool, and Swansea for their help and we apologise if we had missed someone out!

            


AUDI AG