#Coefficient/Friction
16 messages in this thread
Creating an accident reconstruction showing a car crash. My task is to show the
wreck at different speeds. I have the TEMPO routine to plug in the different
speeds. I have available to me stats from the reconstructionist on the
coefficient of friction. Can I use this info with 3DS to help my cause?
Paul
You'd need another KXP that does coefficient of friction calculations. The
dynamics package the Positron is working on will do that, but it's not out yet.
(Positron is at 800/365/1002)
– G
I'll call them. Hope it comes out soon and can help me. Wondering if anyone
would volunteer info on how they have dealt with a similar situation. I was
thinking that with the TEMPO routine I could do this case but now I wonder. I
have a case involving a collision where a car pulled out in front of another
car driving on the highway. Want to show that regardless of the speed of the
car on the highway (say 55 vs. 65 mph) that the wreck would have happened
anyway. Now I'm not so sure I can do this. How can I figure out the stopping
distance at 55 vs. 65 with the software I have. I know that I can show (with
TEMPO) that if no brakes are applied moving 65 vs 55 would get you there
sooner, but not sure how to work in the applying of the brakes (hum???) Any
ideas out there?
I guess I need info from the reconstructionist who did the coefficient
readings, etc. Wonder if he could tell me based on his numbers, the amount of
time to stop at the different speeds, then I could plug that into the length of
the animation along with the known distance the vehicle did travel and I would
have a valid demonstration. Make sense? I'm just thinking out loud here, hoping
to get any insight from someone.
Thanks for lending an ear.
Paul
i guess untill dynamics is out your school physics books should do<G>
i have a good feeling that at siggraph there will be a lot of new tools for
dynamics simulation.
good luck
ara
You are going to need more data: the weight of the vehicle, the road
surface cooefficient of friction, and the surface slope and
direction.
But most important: to be admitted into court the animation must have
a legal foundation presented prior to its being offered into
evidence. That means that someone recognized by the court as an
"expert" has to present verbal testimony describing how the
caluculations were made, how the data was collected, and how the
animtion was created.
That expert would have to be the accident reconstructionist. He or she
is probably an engineer or physicist and would certainly have all the
data you need. You should be working very closely with him because he
will have to "approve" the animation and explain it in court.
Car manufactures often have statistics on the dist that any
particular model need to come to a complete halt at certain given
speeds, you may want to also look into that avenue of information.
Hi, Paul. The other three replies have pretty much answered your
question. I would like to add one more variable…The condition of
the brakes (and thus the stopping distance) of the actual car
involved. It's probably too late to check this…well, it's probably
not crucial.
All good points. I still haven't met the reconstructionist or seen
his findings. It will be interesting to see. I was hoping to keep the
animation as simple as possible. To use it to simply demonstrate the
evidence that the lawyer will be presenting based on the expert
findings of the reconstructionist. In no way can I prove anything in
my animation. I can only offer graphic representation of the facts.
Found out even more today. I can't contact the officer who did the
reconstruction information because the lawyer I am working for doesn't
want it known that they have hired me. Makes things tougher than I
thought.
Be careful. Something is very wrong with the way your accident case
is going. The lawyer has no chance of getting your animation admitted
into court without an expert in reconstruction testifying first. Your
lawyer may want to surprise the opposition with the animation but if
the animation is not produced under the supervision of the expert,
there likely be some serious problems.
Your lawyer is either very smart and way ahead of everyone or very dumb.
I hope you've got at least some of your fee in advance.
Thought I'd give you some insight into this one.
I've been doing these kinds of animations for a few years. Once, an
attorney requested an animation based on the reconstructionist's
data, but did not want the reconstructionist to seen the final
reconstruction animation. The reason is, if the animation looks good
for the attorny's case it will be used, and the proper people
notified (in all my cases I make at least three copies of everything,
one for my attorney, one for the the other attorney and one for the
judge), if the animation looks bad or doesn't put the client in the
best POV, the reconstructionist does not have to testify that one was
made or what it looked like. Noboby knows about it, the attorney was
simply developing the case.
Legally though, all materials can be ordered by the judge to be
submitted to all parties involved, including notes on scratch paper,
napkins, and little animations. Interestingly, this raises questions
about what to save, backups, changes, etc… because everything can
be ordered, everything. Don't get too paranoid though, just be as
honest and ethical as you can about your work. It is no game out
there. Many people use these for selfish gains, others have
literally their lives and livelyhood at stake. I've seen lawyers go
for the limits of a policy, others go after personal property and
part of wages for the better part of a person's life. These
animations are extremely powerful tools, especially when a jury is
involved. And, like any tool, it can be used to build wounderful
things or to destroy.
Also, you have to keep in mind, not all animations are made to go to
court. I often recommendthat an animation be done in the rough just
to figure out what happened and to develop stratagies. An animation
for the courtroom may or may not be required.
On payment, always get a retainer befor you start work. I require 10
hours @ $100 per hour to start. I have never had a job go sour, but
the retainer keeps everyone on their toes and protects you from
loosing too much if the job falls through or payment is not made.
While I'm on the topic, sometimes it is good to ask for a second
payment after the storyboard and rough animation is approved before
going to final output.
Hope I haven't been too long on this one, I'm late on entering this
thread, I'm not sure what has been said already.
Let me know how it goes.
Gregory,
Did you mean to send your message to me? I'm not the one with the case, its
Paul Kakert.
I only do forensic animation and I'm a professional expert witness in the field
of crime scene reconstruction. I'm well aware of the games played by attorneys.
I generally agree with all you've said except that I can't see how an attorney
can get an animation "favorable" to his side admitted without an expert to lay
the legal foundation. An "artist" (animator) could not qualify to testify on
the dynamics of vehicle collisions. Also both sides in a civil action are
required to disclose the evidentiary materials they plan to use in trial — it
is not something that a judge "could" order; it is standard practice and it
would be very, very difficult if not impossible to gain admission of an
evidentiary item without prior disclosure.
Alec Jason
Here's the scoop:
BTW – I appreciate all the input (getting an education on this one)
There is an "expert witness". Someone who has done the calculations. They have
noted where initial impact of the vehicles occured as well as doing a "velocity
deceleration test" Through his testing (and he was asked the main point of this
case) would this have occured at a lower rate of speed vs. what speed they are
presumed driving. His answer was he beleived so but would need more testing but
it is arbitrary based on what point you start reducing the speed (applying the
brakes I assume).
I think for me to continue and to animate the difference in speed he must
provide the information first. I can't make the animation assuming anything, or
best guessing it. Especially if he can't back up the animation with concrete
figures.
Back to the lawyer on this one. Hopefully they can do the numbers for me and
this will still work. I have been facinated by the legal animation business and
have been trying for a year or more to break into this arena. I have not
charged anything as of yet (but then again, I haven't actually done anything
but look at the info to see what if anything I can do.) The arangement is that
if we can do the animation, 1/2 is paid up front and 1/2 due on delivery of the
animation. Probably not agressive enough but I can't see charging anything now
until things have cleared about what info will be given to me to work with.
Thanks again to everyone jumping in on this one.
Paul
Mr Kakert,
The advice given thus far in this thread has been excellent. I wouldn't advise
trying to work in your own version of the accident dynamics; I would stick to
animating according to calculations of a forensic engineer. Having said that,
the following simple formula can be used to predict the approximate "locked
skid distance" for a given initial vehicle velocity. (Contrary to earlier
advice, the vehicle mass is not needed):
0.5 (V^2) where V = vehicle velocity when skid
begins
D = ————– u = coeffiction of sliding
friction between tires
(u) (g) and the road
g = gravitational acceleration (32.2
ft/s^2)
For example, a vehicle travelling at 55 mph (81 ft/s) slams on the brakes and
skids to a stop. If the coefficient of sliding friction between the tires and
the road is 0.75 (varies widely depending road surface conditions and the tire
tread, inflation, etc.), the skid distance would be:
D = 0.5 (81 ft/s)^2 / (0.75) (32.2 ft/s^2) = 134 ft
Or at 65 mph,
D = 188 ft
This is a simplistic evaluation and I only use it for getting a rough idea.
The coefficient of friction is a squirrely value and, as I said, can vary
significantly.
For what it's worth,
-TC
Paul,
I've spent alot of time doing this kind of work as well, and thought I would
throw in my two cents worth. (which may be all it's worth (g))
I noticed some talk about you doing some of your own calculations, but I must
strongly urge you not to do so. Remember at all times that you may very likely
be called to testify in the case, and that you will be asked for your resources
regarding all parts of the animation. If you testify that any of the
calculations were done by you personally, your animation will likely not be
admitted. This is because you are not an expert in the field of accident
reconstruction. As Alec has pointed out, ALL calcs must be done by an expert
witness, and the animation is nothing more than a visual to explain his point
of view on how the accident happened. If the expert is unable to formulate an
opinion based on the facts, an animation is probably not going to help the
case.
Good luck!
Rich Walsh – The Ayres Group
Paul,
>> I have available to me stats from the reconstructionist on the coefficient
of friction. Can I use this info with 3DS to help my cause?<<
I wouldn't. The job of the animator in these circumstances is to illustrate
the information determined by the forensic engineer (position & orientation vs.
time). The best advise is to keep to what you know and let the engineer do the
same.
Ang