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Discussion Starter · #1 ·
If you look at http://hem.passagen.se/jemba/inertia.htm - about half way down the page, you will see that the Jemba inertia based system that is used to produce Stage notes for most pro rallies and some club rallies, produces two very interesting output parameters :

- a speed profile for the whole stage in MPH

- Jemba Safety Index (J/Kg)- "Jemba Safety Index gives average kinetic energy in the car through corners, that is the average energy available to cause damage on places where the car slides"

Two practical drawbacks to this approach are :

- not every US rally uses the Jemba system (especially club rallies)

- the team producing the Jemba notes would have to drive at maximum attack at speeds equal or very close to the speeds that a top national team would drive at, to simulate race conditions, in order for the data to be meaningful (which may not always be possible due to e.g. road not secure, lower spec car used to create notes etc.)

May not be possible in practice, but an interesting thought nonetheless .....


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Faster Mabricator
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>- the team producing the Jemba notes would have to drive at
>maximum attack at speeds equal or very close to the speeds
>that a top national team would drive at, to simulate race
>conditions, in order for the data to be meaningful (which
>may not always be possible due to e.g. road not secure,
>lower spec car used to create notes etc.)

Jemba does not require that the team drive fast. A Coralba odometer which is calculating speed and knows how fast or slow the team is traveling is sending that info to the Jemba accellerometers which calculate the inertia using that speed.
 

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I would love to see the data from LSPR.
It sounds like more useful information than just the Ave MPH.
I imagine it could tell me where to put a chicane and if a chicane would really make the stage safer as so many think.

Who has this info?

Kevin DeLoughary
RallyMaster 2004 LSPR
[email protected]
 

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Dramamine is for DramaQueens
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We have used Jemba at the Rocky Mountain Rally two years runing now. As I recall, the safety index showed our safest stage to be the fastest stage we run, and the most dangerous was one of our slower stages.
Chichane placement is an interesting issue. the most effective placement of a chicane to slow down the stage is in the middle of a long straight, but to make the stages safer, placement would be better just before coming off of a long straight (or open) section into some unusually twisty stuff. This wouldn't dramatically lower the average speed on the stage, but would dramatically increase the safety.
Perhaps looking at mandating chicanes in situations as above.
Possibly requiring chicanes no furthar than 300m from corners where the corner grade decreases by greater than 3 values ...giving a range from 6- to 3+ or 6+ to 3-
Arguably you wouldn't need or have room for a chicane in a 3- to 1+ change ... but I'm thinking aloud here ;-)
The idea is that after several flowing 5's and 6's if you come up on a 3, you are forced to go through a slowing device before entering it ... maybe widen the gap for nationals or 'pro' events? 4 grade points difference?
 

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Discussion Starter · #5 ·
>
>Jemba does not require that the team drive fast. A Coralba
>odometer which is calculating speed and knows how fast or
>slow the team is traveling is sending that info to the Jemba
>accellerometers which calculate the inertia using that
>speed.
>

I understand this, that is part of the beauty of the system.

But for the speed profile to be useful as far as estimating max & average competition speeds during the actual rally would require the Jemba notes preparer to try and duplicate this - this is probably not safe or practical though.

I guess we can still derive average speeds per stage using the old distance / time method. Max speed would still be nice to know though. Any odos out there that store max speed ?

Just thought of one other drawback : if stage conditions were different between preparation and competition running e.g. rain => slippy stages => change in traction level.

The Jemba Safety Index info may still be interesting though e.g. in predicting possible dangerous situation or scenarios as suggested by Kevin and Keith.


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Web site : www.SoCalRally.com
Sponsors : www.VwSpecialties.com www.Parts4VWs.com

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You're thinking too hard

>But for the speed profile to be useful as far as estimating
>max & average competition speeds during the actual rally
>would require the Jemba notes preparer to try and duplicate
>this - this is probably not safe or practical though.

Jemba (or anything else) is not going to estimate max or average speeds. Those are dependant on who is entering the rally and what they are driving, the gear set they have, and a combination of experience vs courage.

>Any odos out there that store max
>speed ?

Coralba for one.
 

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>But for the speed profile to be useful as far as estimating
>max & average competition speeds during the actual rally
>would require the Jemba notes preparer to try and duplicate
>this - this is probably not safe or practical though.

I am sure dave can expalin better, but Jemba does not require the noting crew to drive at speed to extimate WRC car speeds through a stage. Arne was able to predict extremely accurately what the stage times for teh fastest cars would be at rocky using Jemba information. He also told us whre potential jumps were and where the seriously dangerous parts were. I beleive there is a setting for coeficient of grip to make these determinations, bit you also have to remember that Jemba notes are not pace notes, but merely an objective description of the road.

>I guess we can still derive average speeds per stage using
>the old distance / time method. Max speed would still be
>nice to know though. Any odos out there that store max
>speed ?
The Coralba and I beleive the Brantz store max speed, as do many bicycle odometers.
 

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RE: You're thinking too hard

>
>Jemba (or anything else) is not going to estimate max or
>average speeds. Those are dependant on who is entering the
>rally and what they are driving, the gear set they have, and
>a combination of experience vs courage.
>

True, but the experienced folks who did the ProRally notes this year were able to predict stage speeds on each stage with uncanny accuracy...probably a combination of science and art.

The safety indexes are interesting, and have caused some rethinking of some of our stages. It's at least some unbiased data to work with, where all we have now is average speeds and speculation.

Bruce
 

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>But for the speed profile to be useful as far as estimating
>max & average competition speeds during the actual rally
>would require the Jemba notes preparer to try and duplicate
>this - this is probably not safe or practical though.

No it doesn't. Arne (or another user) simply puts in a variable for the type of car (WRC, US Open, Gr.N, F2, Gr.F etc.) and the Coralba calculates the anticipated top and average speeds on stage based on this variable and the accelerometer measurements.

In 2003, Arne's calculations were never more than 2-3% off David Higgins' stage times, using a US Open car to calculate, except for one stage where it rained and David was something like 8% off the pace predicted by the Coralba.

Arne was collecting speeds from Dan, Howard, Mike, and myself for much of the beginning of the year to ensure his calculations were accurate.

Rather than posit on an internet message board about what you _think_ the Coralba does, you should talk to Arne. He did invent the thing.

FWIW, Arne and I have discussed adding a feature to the Stage Index feature to have a scrolling 500m window which indicates avg KE over that window, to help identify specific sections of stages which cause the most risk. Arne's been busy with other stuff, but if we got together and paid for it, this could be added to the Coralba note-making equipment pretty easily.

- Christian

Bjorn Christian Edstrom
www.christianedstrom.com
 

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Discussion Starter · #10 ·
Sorry for any unintended misinformation on the operation and functionality of the Jemba system - it has obviously been well thought out, designed and implemented.

The original point of my post however, was just kinda wondering whether the Jemba system could be used effectively in predicting dangerous scenarios and areas, which could in turn be used effectively to help reduce the number of incidents ?

As always, no system is likely to ever be 100%, account for all conditions etc., and ultimately the driver takes full responsibility for the end result of his decisions and/or actions on stage ... it just seems like the Jemba system has some cool features and I was wondering whether these could be used for some benefit.


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Web site : www.SoCalRally.com
Sponsors : www.VwSpecialties.com www.Parts4VWs.com

Rally - I don't need no stinkin' epi pen to get my adrenalin rush !!
 
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