SHOULD THE WHEEL CONFIGURATION REQUIREMENTS BE CHANGED?
Vehicles with three wheels were allowed in ASC2003. Some of the Sunrayces required four wheels.
What are your thoughts? How to submit your response.
RESPONSES (Generally listed with newest response first.)
RESPONSE#8
To speak to 3 wheelers and rolling over calcs, let me say first that I
agree with Rolla guys who spoke to this earlier. If you design and build
your CG into your car correctly, it can be a very stable design as was
proven in ASC 03 when Minnesota, my team, got a flat tire in the back
wheel on a loose gravel road. The car did not veer to the right or left,
it stayed going straight ahead the whole time, with minor instability.
To calculate rollover, you can calculate the hard turning/cornering g-force
which it takes to flip your car. Minnesota found that it takes
approximately ballpark the same amount of cornering g's to tip the car as
it does to make an ngm tire slip/slide laterally, based on theoretical spec
numbers for friction coefficients. This simple calculation based upon
track, wheel base, and cg location vertically and horizontally are probably
from the same basic equations used in whatever standard Steve Hayslett
speaks of. As for providing measured numbers, this would involve driving
your car like a bat out of hell if you designed it correctly. Theoretical
values is the furthest extent that any cornering data should have to go.
FROM: Jason Halpern,
University of Minnesota - Twin Cities,
Mechanical Engineering,
Team Manager,
Solar Vehicle Project
RESPONSE#7
Another excellent idea [refers to Response#6]. I would rather see a car's stability really
tested rather than limit design ideas. I would think that this test
would need to be such that it could be set up in the same area that the
current braking test is done in. As Dan has pointed out to me, space is
often limited where ever we are having scruitineering and such tests
need to be able to tell the inspectors as much as possible about the car
in as little space as possible.
FROM: Jason Kramb,
University of Michigan Solar Car Team Alumni,
Driver / Chief Aerodynamics and Body Engineer '99,'01
RESPONSE#6
I've seen four wheel vehicles that had questionable stability and three
wheels vehicles that where very stable. Instead of dictating the number of
wheels to get an certain stability, The race should instead dictate a
certain stability and allow teams flexibility in achieving it. Wheel base,
trac, and CG should all be carefully considered in designing a vehicle.
When the original dynamic tests regulations for Sunrayce were drafted over a
decade ago, they probably didn't have a 520 lb solar car going 65 mph in
mind. Now this performance has been achieved, while the dynamic stability
regulations have changed little, if any. Dynamic tests during qualifying
should be updated to reflect the wheights and speeds of today's solar cars.
I propose the addition of a new High Speed Dynamic Regulation. A good test
of this regulation would be weaving 5 cones (TBD spacing) at a TBD speed,
say 40 mph. Because of the higher speeds, this test would occur after a
vehicle has passed all current dynamic tests. Failure to pass this test
would not result in failing to qualify, but would result in a lower speed
cap (say 50 mph) during the race. This makes it in the best interest of
every team to design a more stable car, especially if they plan on going
fast.
FROM: Nathan Rues,
42
RESPONSE#5
This [refers to Respone#3] may be true, and I certainly agree that at the speeds we are now
driving, teams needs to take a very careful look at thier driver safety,
but I would have to point out a couple things.
First, having an inexperienced driver at the wheel of a very experimental
car is not my first idea of raycing safely. I would hope that each and
every team takes driver safety very seriously and as one of the team's
foremost goals. We are now driving at speeds that could kill. Its true
that most of the drivers in the race are somewhat inexperienced, and I
think that is one of the first things that needs to be changed. I know
Michigan has tried to give most of their drivers of the past few cars time
in a prototype chassis on a test track to get them used to what the car is
and is not capable of. There is NO substitute for driving, and teams need
to recognize this and get their cars on the road and get them on the road
early, preferably on a test track or big parking lot where the handling
limits of the car could be explored.
Second, while I've driven solar cars in a race over 8000 miles, and
outside of racing many more, I've never had a real "blowout" of a solar
car tire that has instantaneously changed the handling of the car. In
fact, many flats that I've had, I've barely even noticed, even at 65 mph,
until my chase van told me to pull over. Now, its possible that I've been
pretty lucky or that this is a characteristic of the Michelin tires, but
handling really shouldn't completely disappear with a flat tire to the
point where the driver can't recognize the flat, determine which wheel its
on, and then gently slow the car and move to the curb. How does a
motorcycle, with even one less contact patch, deal with a flat tire? I
don't know, but do the same concepts apply?
Third, stability problems related to traction I think are very different
from problems with the number of contact points. With slick tires, if the
car's dynamics are such that when you hit a puddle the car spins, its
going to spin no matter how many contact patches there are. Honestly, I
do belive that comes down to driver skill again, as in the driver knowing
where the car's tires are, how to avoid obstacles in the road such that
they don't present a problem to how the car drives, and knowing just how
much avoidance is possible given the car's handling. Two wheels right
next to each other is not going to help if they both loose traction from
the same puddle. Knowing how to drive to avoid running through the puddle
will help more.
Fourth, I think returning to the 99 reg requiring four wheels severely
limited the flexibility and innovation that teams had in design. A couple
of teams decided to not participate in the 99 race and went striaght to
WSC instead because they determined that the their design would be
compromised with the fourth wheel. Many teams still went with a four
wheel cars in 01 and 03, and for a variety of reasons. Some for safety,
some for aerodynamics, some for other mechanical reasons, and some for
packaging. But I would hate to see that trade off removed from the
optimization equation. Yes, safety needs to be foremost in a team's mind,
but I hope not in exchange for letting teams find creative ways around the
problem and limiting their ability to create an even more efficient car.
Undertand that 5 out of the 7 Michigan cars have been four wheel cars, so
I'm not necessarily advocating a three wheel car, I just want to don't
want to see a team's design options hampered by the regs.
Regards,
FROM: Jason Kramb,
University of Michigan Solar Car Team Alumni,
Driver / Chief Aerodynamics and Body Design Engineer '99, '01
RESPONSE#4
I just wanted to reply to the last point in this message - about 3
wheeled cars.
I am speaking from the perspective of Principia College and we just built
our first 3-wheeler for ASC 03. We had indeed steered clear of the 3
wheel design because we weren't sure we could build it safely. Along with
better engineering this time around, we added the safety feature of
foam-filled solid tires. The foam we used was manufactured by Carpenter
Co. and is called Rely. I personally spoke with their engineers about
the durability needs for solar raycing since the foam is commonly used in
tractor tires and is not subjected to desert temperatures 10 hours a day.
However, it does not lose its properties until well over 300 degrees
fehrenheit. It adds about 8 pounds weight to an Ecopia tire - which we
accepted since we wanted the safety with our lower resistance 3 wheel
design.
If any teams are interested in using this option you should also know
that you can easily recover the rims but will want to have fresh valve
stems on hand since the foam clogs the stem. While it would not affect
the spin out Arizona had on water - we did experience the equivalent of a
blowout on our foam tire. Our suspension had been slightly off and the
tire did not wear evenly on some particularly rough roads. When the
rubber/kevlar split through the car's steering was affected - a quick
waver off-center as our driver accomodated and them simply a terrible
time steering. This was our first split tire and once we realized what
was up, simply replaced it with another foam-filled tire/rim assembly.
It wasn't pleasant, and really no flat tire situation is, but it could
have been much worse. With even wear we had one tire last a full 3 days
of raycing and another for 2 days - it came away with little holes and
cracks that would have flattened any air tire.
Take what you will and my regards,
FROM: Robyn, Principia College
RESPONSE#3
Even having 2 wheels sandwiched together would make things safer.
It is unlikely to have 2 blowouts at the same time. Most of the
drivers in this race are inexperienced with the specific car, but
that is as much a reason to give them every chance to not kill
themselves. Even though 2 rear-wheel cars are spinnable, all else
being equal, I would think they are less susceptible to spin.
FROM: Jerry Knight-Rubino, University of Arizona 2003 Team
RESPONSE#2
This [refers to Response#1] also was a reg in the 1999 race and was subsequently removed because
so many teams still ended up with a "3 wheel" car with two wheels right
next to each other in the back, basically While both of the cars I've
driven were four wheel cars, my experience shows that problems with
vehicle stability are more a result of good vehicle dynamics design,
weight distribution, and especially driver experience than anything else.
In the hands of an less experienced driver it is just as easy to spin a
four wheel car as it is a three wheeled. I can show you pictures from
Michigan's crash in '01 to show that point. Personally, I believe that
some better measure of vehicle dynamics needs to be performed. I don't
think the figure-8 in its current form is a good test of stability.
Maybe moving back towards somthing like a slalom or a high speed skidpad
would be better?
FROM: Jason Kramb,
University of Michigan Solar Car Team Alumni,
Driver / Chief Aerodynamics and Body Design Engineer '99, '01
RESPONSE#1
Disallow all configurations with only 1 wheel contact
patch behind the center of gravity.
Why: This is a dangerous configuration. All it takes is
a high speed blowout or other loss of traction to
lose control in a spin. Having 2 or more wheels
behind the CG makes uncontrolled spins far less
likely. On the Arizona team, we've had a scary spin
in each of the last two races. This year, we hit a
puddle and ended up on the interstate looking at a
bunch of oncoming traffic. Not good. The
high-performance tires, with their lack of traction
and ease of blowouts/flats make this all the more
likely.
FROM: Jerry Knight-Rubino, University of Arizona 2003 Team
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