Stuck Throttle Prevention

[Denny Trimble]

As you may have seen in the "Northwest FSAE Shootout" thread, OSU recently suffered the consequences of a stuck throttle. Here, I'd like to share everything I've experienced related to stuck throttles, in the hope of preventing future accidents. Please feel free to share your experiences and advice as well.

A stuck throttle is, in my opinion, the most dangerous thing that can happen in an FSAE car, for several reasons:
-It usually happens at full throttle
-It is usually only noticed when it's time to brake
-Most FSAE engines have enough power that all of the driver's effort on the brake pedal will lock up the front wheels, but the engine will overpower the rear brakes and keep on pushing
-With locked-up front wheels, the driver has no directional control over the car
-Most FSAE teams test in cramped parking lots, with nearby obstacles and not much runout room
-Most drivers who experience stuck throttles don't have time to kill the ignition or pull in the clutch (only one of the four I've witnessed has ended this way)

That said, some of the root causes I've seen are:

-Sticky slide-type throttle, which binds at partial throttle under vacuum (our '99 car, possibly UP's car this weekend?)

-Loose hardware on the throttle cable (OSU this weekend)

-Broken cable stop brackets (Our 2003 car)

-Broken return spring on throttle cable (Our 2003 car)

-Driver's left foot covering up right foot (Our 2003 car). This was interesting: before a big straight, we had a bumpy left-hand corner. The driver was floored through the bumpy part onto the large straight, and apparently his left foot bounced over so it was hanging off the right side of the brake pedal, overlapping his right foot. When it came time to brake at the endof the straight, he let off with his right foot and pressed down with his left foot on the brake, which kept his right foot pinned on the throttle. He missed a pole by about 5 feet to the right, at 20 or 30 mph.

Carroll Smith recommended in his books that a push/pull cable, and a toe loop on the pedal, are highly recommended. We agree. We implemented this system in 2003 after the incidents mentioned above, with one addition. We added a lateral stop on the brake pedal to prevent the driver's left foot from covering the throttle.

http://students.washington.edu/dennyt/fsae/pedals-1.jpg

Our ugly pedals still wouldn't have stopped OSU's car because of the nature of their failure, so make sure you are diligent about checking your throttle system as a whole.

Don't let this (or worse!) happen to you (http://fsae.com/eve/forums/a/tpc/f/825607348/m/90110216521/r/34410470621#34410470621)

I almost forgot:
Virginia Tech's 2003 Crash (http://students.washington.edu/dennyt/fsae/VT_crash.jpg)

If anyone from VT would like me to take this down, let me know. I believe it was posted on this forum a while ago.

[Colin]

Great idea for a post Denny, and I think your right, apart from maybe a fire, this is one of the scariest things that can happen to you in a race car
I've had this happen in 2 SAE cars and my historic tarmac rally car. I wasn't in the SAE cars when it happened but was driving the rally car and luckily had time to hit the kill switch before going off the side of a cliff (not fun).
The cause for both the first sae car and the rally car was poorly designed pedal stop that, if the pedal was pushed hard enough, would deflect side ways and catch on the pedal. I think it's easy to underestimate how hard a driver can push on the accelerator pedal when they want to go a bit faster. – SOLUTION Adequately ridged throttle stop
The second cause was dust or dirt getting inside a barrel throttle and causing it to jam open. This happened during a drive day after the event when the whole team had a go and the car had a few "excursions"� off the track.- SOLUTION Push Pull cable and regular inspection and lubrication of throttle
We've also had problems with loose cable hardware causing the throttle to stick partially open, not as scary but still cause for concern. – SOLUTION Don't cut corners during manufacturing
I've got no idea how many times an accelerator pedal gets actuated during the life of an SAE car but I bet it's a hell of a lot so if there is only .1% chance of something occurring IT WILL HAPPEN so make sure to check your system carefully

cheers

[Igor]

Unfortunately this is not a problem unique to FSAE.
From the training at Le Mans this year:



16 June 2005: Tom Coronel crashed hard in Le Mans qualifying
Tom Coronel crashed heavily in the second qualifying session. After the team had to quess why the car had stopped the Dutchman returned with the crew that was send out to the spot earlier. "At the entrance of the Porsche curves the throttle was stuck. We go flat out there so you can assume it was not the most pleasant experience. It was really a shame as things were going well so far. We were going to try out some improvements on the car and improve on our qualifying time at the same time. ", Tom Coronel said.


I'm not part of the race department, but I understand the driver pushed the pedal past the throttle stop where it got stuck.....

Igor
Spyker Cars

[Jarrod]

i have personally experienced a stuck throttle in our 02 fsae car, caused by a torsion spring climbing up its cylindrical guide, and getting up between the top of the cylinder and the throttle lever. After analysing it, we discovered a number of things could have contributed. One was the dirt and grit in a barrel throttle (now running butterfly) producing burrs on the edge of the barrel, and some odd slapped together springs on the throttle cable that bound up. I am now very careful about where the cable gets routed,(no tight curves) where all of the springs sit, and where they can potentially snag under extremes of movement, and how can a driver climb in and upset things. It was a scary moment, and i never want to see it again.

Another close one i have seen is using bike brake cables for throttle, and the cable end jumps out of its housing, sticking the throttle part way open.

[Chris Boyden]

2003 UNM FSAE

I was driving in the endurance race and the throttle kept creeping up on me. i.e. Every time I pushed the gas, the idle got higher and higher. 3000, 5000, 7000.....what the hell?
I was coming around the second passing zone, and floored it....and bam stuck throttle. It really sucked, because I couldn't do a damn thing except hit the kill switch. In addition, we didn't have an adequate return spring on the butterfly throttle. It turns out a cheap and crappy set screw clamp on the straight portion of the linear spring on the pedal let loose and got sticky, holding the throttle every time I pushed it, until it stuck completely. A toe hook/loop would have fixed that one. We made 3 mistakes: no toe loop, crappy return spring, crappy hardware without loctite. '04 was better, but in '05 we used a bike brake cable to open the throttle and left out the closing pull cable. It worries me that it'll stick and somebody will have to experience a scary situation or worse.

[Buckingham]

Our throttle used to be too heavy for the restrictor and we had a restrictor break at the throat about 2-3 years after the car had competed. The restrictor luckily decided to break while I was in the middle of a heavy braking zone. I managed to kill the engine and stop it about 15 ft from a pole.

Usually our old cars get a stuck throttle every once-in-a-while due to a lack of maintenance.

When we ran ETC in '01 and '02. We had the ETC stick ONCE in '01 during one of the very 1st test drives (development phase). Neither car has EVER done it since. Both those cars have since been retired, but they both drove for 2-3 years after they competed.

[nathan s]

Sticky throttles are scary things. We had an incident last fall where we almost lost a freshman during a driving day. The throttle stuck, and either he panicked and hit the gas and the throttle at the same time or the brakes were overpowered. Either way, he pushed into a yellow pull and sheared off the front right corner (looked very similar to the VT pictures). The worst thing was that there was a chain that stretched between the poles that ended up a few inches from the driver (I think that is graphic enough details). Needless to say, we are still in the process of making things a bit safer.

[Steve Yao]

Chris,

I chose not to install the return cable because the cable itself was introducing a good deal of stiction to the throttle system. There was not enough time left to try other cables, so I went with a set screw that deformed the cable(providing some mechanical attachment besides friction) and doubled the cable back on itself.

I hope to remedy the situation before UTA.

[Bowtie Man]

After our first acceleration run, a loose nut stuck our throttle open and the driver feathered the clutch bouncing it off of the rev limiter until i got a chance to kill the engine. We suffered a blown clutch (thanks again to U of Arizona for the replacement) but in this incident he easily could have killed the engine and rolled it out of the way. Prevention is definitely the best way to go, but training a driver to deal with the situations that can arise is also a good idea.

Luc
University of Manitoba

[Chris Boyden]

Steve,

Some kind of positive return mechanism would be
awesome. It really sucks to have the throttle stick wide open. Sorry, didn't mean to be an ass. It just worries me that it'll happen again.

Chris

[Fender]

Where do most teams connect the throttle cable? I was considering using a belcrank and connecting it at the bottom since it was always getting in our way last year. I havn't seen it connected anywhere other than directly off the pedal, right near the footpad.