(Note: LANDRACING.COM donations are not tax deductible)


This is a public forum. The opinions expressed here don't
necessarily reflect the feelings of The Folks That Run The Site (that's us)
unless we explicitly say so, ok?


Author Topic: Lift Light  (Read 2430 times)

0 Members and 1 Guest are viewing this topic.

Offline ggl205

  • Sr. Member
  • ****
  • Posts: 778
  • Age: 73
  • Location: Wichita, Kansas
  • G/FL 218.282 since 1995. G/FL record since 1993.
Lift Light
« on: February 21, 2020, 10:08:10 AM »
Over the decades, LSR racers have come up with a variety of devices to determine if their cars are aerodynamically lifting to the point of loosing control. Unless you have wind tunnel data, the only other way to determine if front wheels are still on the ground, was to see if the car still responds to driver input. Of course, this may be too late and a spin or crash may ensue.

Off and on, I have given some thought to this problem. Everything from mechanical devices to simple electrical solutions which all met with impracticality or outright failure. After watching one of Danny Tompson's in-car runs depicting what I was told is an operating lift light. Once again, interest in a workable and reliable lift light began anew.

I mentioned this problem to a friend who took it upon himself to develop a very practical and economical device that has many features other than measuring lift. It is all based on a laser that shoots photons to the ground, bounce back, are collected and time they take to go round trip is converted to distance. Run data is saved and can be used to determine lift at any point in the run. Data can also be downloaded into Google Maps for a visual on where any serious lift may have occurred. This is the general idea but there is much more capability in this device but don?t want to take up too much space in the introduction. Time will tell if this device works in a salt environment but steps are being taken to shield everything much like you would with other electronics in the car.

Photos attached (left to right) are of the light box. Green indicates satellite acquisition and red indicates when both lower and upper limits have been reached. Center box is the computer and box on the right is the laser.

John
« Last Edit: February 21, 2020, 11:00:34 AM by ggl205 »

Offline Lemming Motors

  • Sr. Member
  • ****
  • Posts: 405
  • Location: United Kingdom
Re: Lift Light
« Reply #1 on: February 21, 2020, 10:15:21 AM »
I like it John.

I actually noodled on using a laser distance gauge (the diy type) but they get inaccurate at close range.
I look forward to hearing how your device works in practice but I fear your forward speed will mean that by the time the photons are taking the return trip from the salt they will have been left behind and missing the sensor altogether  lol8
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline ggl205

  • Sr. Member
  • ****
  • Posts: 778
  • Age: 73
  • Location: Wichita, Kansas
  • G/FL 218.282 since 1995. G/FL record since 1993.
Re: Lift Light
« Reply #2 on: February 21, 2020, 10:26:31 AM »
John:

The laser chosen has a user definable range. Chose one in the range you need and they are very accurate. As to speed these photons travel; I asked the same question and was told the speed spec for photons. The short answer is they travel at the speed of light so no way will I go faster than that (but one could dream).

John
« Last Edit: February 21, 2020, 11:03:31 AM by ggl205 »

Offline ggl205

  • Sr. Member
  • ****
  • Posts: 778
  • Age: 73
  • Location: Wichita, Kansas
  • G/FL 218.282 since 1995. G/FL record since 1993.
Re: Lift Light
« Reply #3 on: February 21, 2020, 10:36:57 AM »
One feature that will be added is to automatically start data acquisition at 30 mph and shut it off at 30 mph. This eliminates the driver forgetting to turn the bloody thing on!

John
« Last Edit: February 21, 2020, 11:04:02 AM by ggl205 »

Offline TD

  • Full Member
  • ***
  • Posts: 95
Re: Lift Light
« Reply #4 on: February 21, 2020, 02:03:28 PM »
Let's assume (and we know what assumptions do!) that the device works by measuring the time it takes for a pulse of light to travel from the laser to the salt and back to a sensor, e.g., a simple time/distance measurement.

Speed of light in a vacuum is about 30,000,000,000 cm/sec.  Let's say the laser and sensor are mounted 10 cm (about 4") off the ground.  The path length to the salt and back is therefore 20 cm, and the light (pulse) will require 0.667 nanoseconds (6.67E-10 sec) to traverse the 20 cm path. 

Let's further say that the high limit is set to 20 cm, meaning the car has lifted 10 cm (about 4").   The light pulse will now require twice as much time as before, or 1.33 ns (1.33E-9 s), to traverse the 40 cm path (20 down, 20 back). 

In order to detect this change, the controller will need to be able to resolve the difference between 0.667 ns and 1.33 ns, a difference of 0.66 ns.  Accurate measurements usually require a resolution 10x better than what you are trying to measure, meaning that the controller might have to be able to resolve 0.066 ns.  Furthermore, the jitter in the timing path must be substantially less than that amount (this is the really hard part).

To put this in perspective, 0.066 ns is the equivalent to about 15 gigahertz.  Pretty demanding, and impressive if it can be made to work.  Perhaps the device uses a more sophisticated measurement approach (Doppler?).

Meanwhile, if mounted to a car moving at 700 MPH (about 313 m/s), the car will have moved (313 m * 1.33E-9 sec) = 4.16E-7 meters, or about 0.016 thousands of an inch, while the laser pulse is meandering its way to the salt and back.

Good stuff.  Curious to learn how the device actually works.

Offline ggl205

  • Sr. Member
  • ****
  • Posts: 778
  • Age: 73
  • Location: Wichita, Kansas
  • G/FL 218.282 since 1995. G/FL record since 1993.
Re: Lift Light
« Reply #5 on: February 21, 2020, 03:28:19 PM »
TD, I have forwarded your comments and questions to the developer. He can address the more technical aspects of the device. When he responds, I will post it here. For reference, my ground clearance will be between 2?-2.5? with total travel in compression of .5?. Rebound is rubber bumper limited to .5? from static ride height.

John

Offline TD

  • Full Member
  • ***
  • Posts: 95
Re: Lift Light
« Reply #6 on: February 21, 2020, 04:13:22 PM »
Thanks John.  Note I'm not saying it cannot work, it may be entirely feasible given modern microelectronics.  I don't have a laser, LIDAR, or radar background but I did spend a lot of time working on precision time and frequency distribution in (Internet) packet routers.  A nanosecond here, a nanosecond there, and pretty soon your precision frequency and/or time stamp ain't so accurate.  Your friend probably has it all figured out and if so good on him, certainly the packaging looks good!

Thanks, best
Tim


Offline ggl205

  • Sr. Member
  • ****
  • Posts: 778
  • Age: 73
  • Location: Wichita, Kansas
  • G/FL 218.282 since 1995. G/FL record since 1993.
Re: Lift Light
« Reply #7 on: February 21, 2020, 04:42:18 PM »
Tim, one of the great things about posting here are the helpful comments offered. So many people with varied and experienced backgrounds make for valuable information. All comments are welcome.

John

Offline datadoc

  • New folks
  • Posts: 14
  • Age: 78
  • Location: Highland,Utah
Re: Lift Light
« Reply #8 on: February 21, 2020, 05:15:16 PM »
Hi,
 I'm not sure the ride height sensor works the way it's been presented. At Racepak the lazer distance sensors we sold to the drag racers are not based on flight time but where the returned light beam strikes on a angled sensor built inside the sensor. This forms a triangle and the distance is resolved from that info. The way we did it with the Turbinator was to use analog linear position sensors mounted on the suspension. 0-5 volts was equal to full travel of the sensor which can be ordered in one inch increments. The system recorded at a accuracy of one part in 1024 or for a 4 inch travel sensor was a resolution of .004 in.
   Ron

Offline manta22

  • Hero Member
  • *****
  • Posts: 3592
  • Age: 81
  • Location: Tucson, AZ
  • What, me worry?
Re: Lift Light
« Reply #9 on: February 21, 2020, 06:04:34 PM »
Ron, you are right. The triangulation method works very well at short ranges. Conversely, the time-of-flight measurement system is optimum at long range. I worked on some distance measurement systems for detonating a warhead at a precise distance from a target using the triangulation method. It was simple & accurate.
Regards, Neil  Tucson, AZ

Offline Doc B.

  • Full Member
  • ***
  • Posts: 158
  • Age: 64
  • Location: Poulsbo, WA
    • Bottlehead Corp.
Re: Lift Light
« Reply #10 on: February 21, 2020, 06:29:28 PM »
If you are concerned with knowing about lift before getting to the point of no return, would measuring the down/up force on the body or wheel rather than distance to a potentially uneven track surface be any more accurate? If you are concerned with the point where the wheel is no longer in contact with the surface, what about a simple electrical contact that is closed when the suspension reaches (or gets close to) full extension? - assuming this is a moving suspension.

Offline manta22

  • Hero Member
  • *****
  • Posts: 3592
  • Age: 81
  • Location: Tucson, AZ
  • What, me worry?
Re: Lift Light
« Reply #11 on: February 21, 2020, 06:58:59 PM »
Doc, the distance measurement gives a valuable data point on the lift/downforce on the body at high speed. Kalman filtering will smooth out the uneven surface effects.
Regards, Neil  Tucson, AZ

Offline Stainless1

  • Administrator
  • Hero Member
  • ***
  • Posts: 7672
  • Age: 69
  • Location: Near Furley and Kechi KS
  • Robert W. P. "Stainless" Steele
Re: Lift Light
« Reply #12 on: February 21, 2020, 10:57:18 PM »
I was present for the demo and asked questions.... the guy is pretty sharp... I think we can come up with a good test plan... and yes, the idea is to use the data to discover it a car is lifting as it goes faster.... or if it is compressing... The test fixture had a little slider and worked well in a static test... but I agree a good dynamic test is the logical next step.  Should be easy since John has a couple of working units.
Stainless
Red Hat 228.039, 2001, 65ci, MSA Bockscar Lakester with a little N20 
MSA Bockscar Lakester #1000 my fastest mile 245 and change, 84 ci turbobusa motor... but Corey's 233 MPH H/BFL record is still 3MPH faster than mine.

Offline Peter Jack

  • Hero Member
  • *****
  • Posts: 3717
  • Age: 76
  • Location: Calgary, Alberta
Re: Lift Light
« Reply #13 on: February 21, 2020, 11:30:03 PM »
I was just thinking (and that can be dangerous) shouldn't there be a sensor at each end of the car. We're not really worried if the front end lifts as long as the rear lifts an equivalent amount. The problem comes when the front lift starts to exceed the rear. Excessive lift in the rear can also cause problems. I guess both ends should be measured and the rear should exceed the front within certain parameters. With this theory I'm assuming there should be a certain small amount of rake in the chassis.

Pete

Offline ggl205

  • Sr. Member
  • ****
  • Posts: 778
  • Age: 73
  • Location: Wichita, Kansas
  • G/FL 218.282 since 1995. G/FL record since 1993.
Re: Lift Light
« Reply #14 on: February 22, 2020, 04:03:39 AM »
Pete:

There will be chassis rake. Plan calls for between 2?-2.5? ride height at front and 3.5?-4? at rear.

I agree with a rear sensor and it was discussed. One concern was salt dust generated by air flow and how it would affect the sensor. Proof of concept is more important so front sensor only for now.

A dynamic test was conducted on Chuck?s (the developer) road car. Seemed to work well on a street car but the great white is a different story altogether.

I asked Chuck to get more technical on this thread. He understands all of what has been discussed so far and will soon respond. If it helps, Chuck is working with LIDAR technology.

John
« Last Edit: February 22, 2020, 04:18:19 AM by ggl205 »