gt0297a@prism.gatech.EDU (Tim Drury) (06/17/91)
is there an accurate, *cheap* method of measuring vehicle speed without measuring off the front or rear wheels? this is to be used in a proto- type traction control system on a race car. the speed of the rear wheels will be compared with the true vehicle speed to determine if traction is lost. since the front wheels will rotate at differing speeds in turns they can't be used. is there an easy way to use infrared doppler or something like it? -tim drury gt0297a@hydra.gatech.edu
csmith@ux1.cso.uiuc.edu (chuck smith) (06/18/91)
gt0297a@prism.gatech.EDU (Tim Drury) writes: >is there an accurate, *cheap* method of measuring vehicle speed without >measuring off the front or rear wheels? this is to be used in a proto- >type traction control system on a race car. the speed of the rear >wheels will be compared with the true vehicle speed to determine if >traction is lost. since the front wheels will rotate at differing speeds >in turns they can't be used. >is there an easy way to use infrared doppler or something like it? The easiest way to impliment a traction control is to measure vehicle acceleration and compare it to tire acceleration. This is in essence what ABS and other current traction control systems do. Its not too cheap though. >-tim drury >gt0297a@hydra.gatech.edu -- ------------------------------------------------------------------------ chuck smith U. of Illinois The purpose of diplomacy is cwsqbm@uiuc.edu at Urbana-Champaign is to prolong a crisis - Spock ------------------------------------------------------------------------
lusky@ccwf.cc.utexas.edu (Jonathan R. Lusky) (06/18/91)
In article <31487@hydra.gatech.EDU> gt0297a@prism.gatech.EDU (Tim Drury) writes: >is there an accurate, *cheap* method of measuring vehicle speed without >measuring off the front or rear wheels? this is to be used in a proto- >type traction control system on a race car. the speed of the rear >wheels will be compared with the true vehicle speed to determine if >traction is lost. since the front wheels will rotate at differing speeds >in turns they can't be used. >is there an easy way to use infrared doppler or something like it? > >-tim drury >gt0297a@hydra.gatech.edu Actually, in a turn, all four wheels should be rotating at different speeds if y you are using a differential in the rear. I think most traction control system s monitor all four wheels, and only perform corrections when the difference is (in wheel speeds) greater than possible without wheelslip (spin or lockup). Jonathan R. Lusky University of Texas at Austin lusky@ccwf.cc.utexas.edu Society of Automotive Engineers (512) 471-5399 Chairman, Natural Gas Vehicle Project ETC 1.204F IRC Admin, minnie.cc.utexas.edu
carl@ecr.mu.oz.au (Ivan the TERRIBLE) (06/18/91)
In article <31487@hydra.gatech.EDU>, gt0297a@prism.gatech.EDU (Tim Drury) writes: > is there an accurate, *cheap* method of measuring vehicle speed without > measuring off the front or rear wheels? this is to be used in a proto- > type traction control system on a race car. the speed of the rear > wheels will be compared with the true vehicle speed to determine if > traction is lost. since the front wheels will rotate at differing speeds > in turns they can't be used. > is there an easy way to use infrared doppler or something like it? > > -tim drury > gt0297a@hydra.gatech.edu Unfortunatly, it is very difficult to acuratly measure your speed by any cheap means. Front wheels is probably more than adequite for your purposes, and a relativly cheap way of doing this is to buy a rally computer, eg Terratrip or such, which has a magnetic probe which works off the front wheels It would PROBABLY be accurate enough. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Carl Ivan the terrible @ chemeng stinkfarm @ unimelb Australia DEATH to Automatic transmissions, Front Wheel drive and Front Wheel Handbrakes Sideways forever Carl@ecr.mu.oz.au (it takes BALLS to use UNIX)
gt0297a@prism.gatech.EDU (Tim Drury) (06/18/91)
after reviewing all the responses (thanx folks) i believe a doppler measuring system to be to costly and complex for a $6000 car budget. it seems that i will invest in 4 magnetic proximity sensors on all four wheels. if the speed of either rear wheel exceeds some average of the front two then i will reduce the power of the engine. i could spend a few hours determining vehicle speed from both front wheels (and angle probably) but it would probably be better if i built the system with some flexibility and simply tweaked the system on the test track until i get satisfactory results. i'm still listening for alternatives... -tim drury email: gt0297a@hydra.gatech.edu
tedwards@aplcomm.JHUAPL.EDU (Edwards Thomas G S1A x8297) (06/19/91)
In article <31529@hydra.gatech.EDU> gt0297a@prism.gatech.EDU (Tim Drury) writes: >after reviewing all the responses (thanx folks) i believe a doppler measuring >system to be to costly and complex for a $6000 car budget. it seems that Ramsey Electronics sells a radar speed indicator kit for under $100. You make the gun out of a tennis ball can which you provide :-) I imagine one could take the LED output lines and utilize them for computer sensing. -Tom
gil@sequent.com (06/19/91)
In article <31487@hydra.gatech.EDU> gt0297a@prism.gatech.EDU (Tim Drury) writes: >is there an accurate, *cheap* method of measuring vehicle speed without >measuring off the front or rear wheels? this is to be used in a proto- >type traction control system on a race car. the speed of the rear >wheels will be compared with the true vehicle speed to determine if >traction is lost. since the front wheels will rotate at differing speeds >in turns they can't be used. >is there an easy way to use infrared doppler or something like it? It would seem to me that the inaccuracy caused by the front wheels turning on different radii would not be any worse than the inaccuracy of a doppler on a cornering device, since the doppler would only measure the velocity in one plane, while the vehicle would be moving in two planes. Why not do the same trick that car tests do, and use an electronic speedo on a bike wheel attached to the rear bumper? Gil -- Gil Meacham ____ ____ _ __ __ gil@sequent.com / / /___/ / / / (503) 578-3170 /___/ /___ / / / ____/ ==============>>>
jbs@en.ecn.purdue.edu (Spaggie) (06/20/91)
I have been catching the end of this posting, but I had a few
ideas I thogh I would throw in. While working at Allied Signal
this last fall, I was involved in closed loop DSP control systems.
I was also involved in using laser interferometry to measure
vibration on an engine (aircraft). I too had an interest
in determining the speed of my car, but not for ABS. I was just
interested in what my real speed was. (Speedos are so inaccurate
these days at speeds about 70 MPH). After discussing the idea with
several people the following idea developed.
When you shine a laser on a diffuse surface, you get what is called
a speckle patter. This pattern can be seen with the eye. As you move
the laser across the surface, the pattern moves with it. If one were
to hook up a laser to shoot at a spot on the ground, and pick up the
signal (amplitude) with a ccd array, then store the resultant frame in
the dsp. Next you would grab another frame (just a few msecs apart)
and compare them in the DSP. (you could do a cross correlation to find
the phase difference.. DSP is fast in that respect) If you can tell
the amount the ground has moved (knowing the projected width of the
CCD array), and the time frame at which it occured, you can determine
the speed relative to ground.
Does this sound feasable?.. with a laser diode, and Analog
Devices 2105 DSP ($10!!!), and a CCD array, it would
no be too expensive...
=================================================================
Jeff Sponaugle Allied Signal Aerospace, ECD
938 Roberts St Dept 862, Optical Engineering
South Bend, IN 46625 717 N Bendix Dr.
(219) 234-5103 South Bend, IN 46620
Internet: jbs@ecn.purdue.edu (219) 231-3063
=================================================================jwm@sppy00.UUCP (Jeffrey W. May) (06/20/91)
Two ideas on this one:
1). Put a 'mark' (either with white paint, or attach a small magnet) on
the driveshaft and mount a sensor next to it to count the revolutions.
This number could then be scaled with a multiplier circuit, depending on
the tire size and the gearing in the differential, to yield the car speed.
Since the driveshaft-rotation-to-tire-rotation is a fixed proportion this
would give a reasonable result. Be careful if you do this because the
driveshaft is balanced and if you throw it too far off balance you will
cause excessive wear in the universal joints and seals.
2). See if one of the electronic speedometer sensors will fit your car.
My car has one of those digital dashboards and I looked up in the technical
manual how the speedometer works. On the side of the transmision there is
a mount where the speedometer cable bolts in, for the electronic
speedometer there is a sensor that goes there instead. It has a
gear/fitting similar to a spedometer cable so it will fit right in. This
sensor does essentially what #1 above does, it monitors the rotation of the
output gears and produces voltage pulses on a wire. The dashboard
controller has a counter/multiplier that translates this to decimal digits
for display.
You will have to do some road tests and math to figure out what multiplier
values to use for your car.
Hope this spawns some more ideas!
-Jeff
--
______________________________________________________________________________
Jeffrey May UUCP: jwm@sppy00.UUCP Internet: jwm@rsch.oclc.org
OCLC - Online Computer Library Center
Dublin, Ohio "Heavens they're tasty and expeditious."whinery@hale.ifa.hawaii.edu (Alan Whinery) (06/22/91)
In article <1254@sppy00.UUCP> jwm@sppy00.UUCP (Jeffrey W. May) writes: > >Two ideas on this one: >(...) >Since the driveshaft-rotation-to-tire-rotation is a fixed proportion this >would give a reasonable result. Not Always true -- when the car goes around a corner, the ratio changes. The differential allows each drive wheel to turn at a different speed. -- ========================================================================= | D. Alan Whinery| The Institute for Astronomy, University of Hawaii | | Technical Genius| Internet: whinery@hale.ifa.hawaii.edu | =========================================================================
esupg@warwick.ac.uk (Andrew Bargery) (06/22/91)
I`ve only just caught this thread, so forgive me if I am repeating. I am
currently building a car speedo/odo trip computer for competition use. When I
was looking at commercially available units, the use two types of pick-up :
speedo cable drive : a sensors that connects to the speedo drive. I believe
they are usually hall effect devices.
inductive pick-up : This seems a better method. Uses a standard inductive
proximity switch triggered of the rear of the wheel
bolts. I fitted one on the front strut of my car, with
the sensor close to my brake disc. They cost about 25
pound over here. It is recommended that the sensor be
used on a non-driven wheel, however, the validity of
that depends on whether you need the sensor for road-
speedo use or competition-odo readings. Email if you
want more details...
------------------------------ esupg@uk.ac.warwick.cu -----------------------
DISCLAIMER: Andrew University of Warwick, Coventry, UK.
Bargery 154 Brunswick St, Leamington, CV31 2ER, UK.
I plead the 5th... vox : +44 926 881264rhaar@albertgmr.com (Robert L. Haar CS50) (06/22/91)
In article <13571@uhccux.uhcc.Hawaii.Edu>, whinery@hale.ifa.hawaii.edu (Alan Whinery) writes: |> In article <1254@sppy00.UUCP> jwm@sppy00.UUCP (Jeffrey W. May) writes: |> > |> >Two ideas on this one: |> >(...) |> >Since the driveshaft-rotation-to-tire-rotation is a fixed proportion this |> >would give a reasonable result. |> |> Not Always true -- when the car goes around a corner, the ratio changes. |> The differential allows each drive wheel to turn at a different speed. |> Even if it was, this would give you wheel speed (rotational), not vehicle speed. Ther are long term variations like tire wear and tire pressure changes that effect the relationship. Then there are all kinds of short term variations that come about from wheel slipage. MOST of the time, these are negligble. The problem is that for ABS or traction control, the times when you want to do something is exactly when the wheel speeds are not the same as vehicle speed. Bob Haar InterNet : rhaar@gmr.com Computer Science Dept., G.M. Research Laboratories DISCLAIMER: Unless indicated otherwise, everything in this note is personal opinion, not an official statement of General Motors Corp.
svoboda@motcid.UUCP (David Svoboda) (06/22/91)
From article <1991Jun20.024446.18473@en.ecn.purdue.edu>, by jbs@en.ecn.purdue.edu (Spaggie): > > When you shine a laser on a diffuse surface, you get what is called > a speckle patter. This pattern can be seen with the eye. As you move > the laser across the surface, the pattern moves with it. If one were > to hook up a laser to shoot at a spot on the ground, and pick up the > signal (amplitude) with a ccd array, then store the resultant frame in > the dsp. Next you would grab another frame (just a few msecs apart) > and compare them in the DSP. (you could do a cross correlation to find > the phase difference.. DSP is fast in that respect) If you can tell > the amount the ground has moved (knowing the projected width of the > CCD array), and the time frame at which it occured, you can determine > the speed relative to ground. Outstanding. But I could envision a problem with an inconsistant ground surface, as well as a problem illuminating the ground sufficiently from under the car to be picked up reliably by the receiver. A solution might be to actually shine the laserdiode and pickup at the top of the tire, inside the well. The tread surface would necessarily be moving at the same speed as the ground (except in a skid) and the speed reading would be independent of tire wear, pressure, etc (unlike the transmission or driveshaft methods). The laser/pickup package should be mounted directly above the front tire to deal properly with turning and the up-down supsension motion, or above a back tire. Dave Svoboda, Motorola CID, RTSG, Arlington Heights, IL uucp => {uunet|mcdchg|att}!motcid!svoboda internet => svoboda@void.rtsg.mot.com UNIX was written so a couple of hackers could run space war easier.
csmith@plains.NoDak.edu (Carl Smith) (06/22/91)
In article <4746@guppie4.UUCP> svoboda@motcid.UUCP (David Svoboda) writes: >From article <1991Jun20.024446.18473@en.ecn.purdue.edu>, by jbs@en.ecn.purdue.edu (Spaggie): >> [description of laser speckle patter speed measurement system deleted] >Outstanding. But I could envision a problem with an inconsistant ground >surface, as well as a problem illuminating the ground sufficiently from >under the car to be picked up reliably by the receiver. Although this system would avoid all the problems of tire wear, tire pressure, tire slip, etc, I see one real simple problem. Dirt. Anything that has a direct "view" of the road surface will soon be covered with a layer of dirt, even if the road isn't wet and muddy. Laser beams don't go far through mud. I don't know how this could be solved... Maybe mount the laser and detector behind a glass window with a little window wiper... :) > Dave Svoboda, Motorola CID, RTSG, Arlington Heights, IL > uucp => {uunet|mcdchg|att}!motcid!svoboda > internet => svoboda@void.rtsg.mot.com > UNIX was written so a couple of hackers could run > space war easier. ------------------------ Carl D. Smith Jr. csmith@plains.nodak.edu ------------------------
ssave@ole.UUCP (Shailendra Save) (06/23/91)
Here's an idea:
Put under your front bumper (or near the front) an RF point source (say
about 8MHz) pointing downwards. Along the underside of your car (in
line with the source, place sensitive RF pickups, say about every
2cm. Now, since the car is about 2m long, you will be able to have
a measurement of 100mph. This is how:
L___________________________________________________I <-underside of car
\\ I I I I I I I I I I I I I I I I I I I I I I
\ /
\ /
\ /
\ /
\ /
------------------------------------------------------ <- road surface
The \\ in the front is the RF source. The I I I I 's are the RF
pickups. Now, using a micro, you are going to have to send pulses
of RF every millionth of a second. Find out which of the sensors
receives a signal. Then over a hundredth of a second, average the
number of the sensor. The reason why I say millionth and
hundredth, is that I expect that there will be some pits etc on the
road and so you will get erroneous reading sometimes. This will be
averaged out by taking a large number of samples. Also, averaging
every hundredth of a sec will make it possible to update the speedo
fast enough to give it real-time value.
On real bumpy roads, keep your eyes on the road! Don't look at your
speedo. :-)
Shailendra
ssave@caen.engin.umich.edu
sumax!ole.uucp!ssave
PS: someone could actually calculate the wavelength required.gt0869a@prism.gatech.EDU (WATERS,CLYDE GORDON) (06/24/91)
In article <10922@plains.NoDak.edu> csmith@plains.NoDak.edu (Carl Smith) writes: >In article <4746@guppie4.UUCP> svoboda@motcid.UUCP (David Svoboda) writes: >>From article <1991Jun20.024446.18473@en.ecn.purdue.edu>, by jbs@en.ecn.purdue.edu (Spaggie): >>> [description of laser speckle patter speed measurement system deleted] >>Outstanding. But I could envision a problem with an inconsistant ground >>surface, as well as a problem illuminating the ground sufficiently from >>under the car to be picked up reliably by the receiver. >Anything that has a direct "view" of the road surface will soon be >covered with a layer of dirt, even if the road isn't wet and muddy. >Laser beams don't go far through mud. >I don't know how this could be solved... Maybe mount the laser and >detector behind a glass window with a little window wiper... :) I made a suggestion to the original poster that I will share here due to the apparent interest: I read a while back about how F1 racing teams wanted to have info on car-ground speed, ride height, etc. Their method seemed a little more practical- They used an ultrasound source (I think) and bounced sound off the ground. The transmitter was surrounded by little directional recievers (mics?) The time the beam took to come back compared to the shift laterally or longitudinally of the beam reflected referenced to the original transmission position can easily be used to calculate vehicle speed (a simple ratio) This should be usable, if the transmission pulses are fast enough, to not only give ground speed, but ride height in relation to time also. I have no idea how the reception worked, but I think the transmitter was placed in a small waveguide tube.(to concentrate the beam into a small area) Anyone with more knowledge on ultrasound mapping could be of much more help. Regards, Gordon. -- WATERS,CLYDE GORDON-Georgia Institute of Technology Atlanta Ga 30332 ******<LANGUAGE IS A VIRUS! - Laurie Anderson-Home of the Brave>******* uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!gt0869a Internet: gt0869a@prism.gatech.edu
nagle@well.sf.ca.us (John Nagle) (06/25/91)
Prototype hardware for measuring speed and direction by looking down at the road exists and has been successfully field-tested. If there is serious interest in licencing the technology, I can put you in touch with the manufacturer. John Nagle
andyw@aspen32.cray.com (Andy Warner) (06/29/91)
A little while ago (ie long enough that it's expired from our nntp server), someone posted an idea for bouncing radio off the road under a car and figuring out how fast you were going from testing which antenna from an array gave the best signal. Someone tell me this was a joke, please. How far is the car going to move in the time it takes for the signal to bounce back, at say 60MPH .. Well my rough calculations say about .. 2nS (assuming a 50cm path, s = 3x10^8 m/sec - rough, but the right order of magnitude). So how far does your average 60MPH Subaru move in 2nS ? Roughly 0.000006 cm. I think the engineering tolerances might be a little tight here.. Now, I could have the wrong end of the stick here, but I don't think so. -- andyw. (W0/G1XRL) andyw@aspen.cray.com Andy Warner, Cray Research, Inc. (612) 683-5835