Post by thread:Quiz on detecting lateral movement

How could you detect (for computer input) lateral movement from within an object when no contact can be made with the ground and there are no obstacles around to bounce a signal off of. For example: How would you detect that the rear end of a car has started to slide sideways (on ice) ? The front wheels are still pointed forward (you have not started to turn the wheel to compensate). There are no walls around to bounce a signal off of. Assume you have your breaks locked up and therefore cannot use comparison of wheel velocities. Assume also, that you cannot attach any sensors to the ground, wheels or be manually activated. Remember that most movement sensors would not be able to tell the difference between laterally sliding on ice and a sharp turn. An optical sensor would detect ice but not that your sliding on it. How would you do it?? Gene

How about a sprung LVDT (Linear Variable Diferential Transformer) in car. The G Force caused would cause its weighted ends to move which could be detected. An optical sensor could detect the ice. This system is used in some lifts to detect a fast drop. The Zero G conditions let the weight lift on the springs force. Note: these devices are expensive. Tim At 12:25 10/01/97 PST, you wrote: {Quote hidden}>How could you detect (for computer input) lateral movement from within > an object when no contact can be made with the ground and there are no > obstacles around to bounce a signal off of. > >For example: How would you detect that the rear end of a car has > started to slide sideways (on ice) ? The front wheels are still > pointed forward (you have not started to turn the wheel to > compensate). There are no walls around to bounce a signal off of. > Assume you have your breaks locked up and therefore cannot use > comparison of wheel velocities. Assume also, that you cannot attach > any sensors to the ground, wheels or be manually activated. Remember > that most movement sensors would not be able to tell the difference > between laterally sliding on ice and a sharp turn. An optical sensor > would detect ice but not that your sliding on it. > >How would you do it?? > >Gene >

Hello PICLIST My suggestion to solve this problem would be to use an ultrasonic transducer, or preferably 2, pointed at an angle to the road, and together with a pair of ultrasonic receivers utilize the Doppler-effect. If it is made as a bridge, it should be possible to get a signal for even very small movements. The alternative would be a gyroscope, but then we are talking money - mucho money!. At 12.25 10-01-1997 PST, you wrote: {Quote hidden}>How could you detect (for computer input) lateral movement from within > an object when no contact can be made with the ground and there are no > obstacles around to bounce a signal off of. > >For example: How would you detect that the rear end of a car has > started to slide sideways (on ice) ? The front wheels are still > pointed forward (you have not started to turn the wheel to > compensate). There are no walls around to bounce a signal off of. > Assume you have your breaks locked up and therefore cannot use > comparison of wheel velocities. Assume also, that you cannot attach > any sensors to the ground, wheels or be manually activated. Remember > that most movement sensors would not be able to tell the difference > between laterally sliding on ice and a sharp turn. An optical sensor > would detect ice but not that your sliding on it. > >How would you do it?? > >Gene > > Med venlig hilsen / Best regards Poul Bundgaard Phone +45 86 65 13 92 Pr¾stev¾nget 4 Fax +45 86 65 13 92 R¿dding Mobil DK-8830 Tjele Denmark E-mail: spam_OUTp_bundgaardTakeThisOuTvip.cybercity.dk

Wow! I don't know what your project is, but it's a great challenge. The way I'd do it would probably use an accelerometer mouned parallel to the rear axel. I'd then connect a sensor to the steering mechanism. If the acellerometer detects lateral movement and the steering wheel is pointed straight ahead, a skid is taking place. Things get trickier when the car is suppoed to be turning. I suppose you'd have to determine empirically the relatinships between speed, turning radius, and accelerometer detection. Then compare the three readings. If the accelerometer output is beyind the specs for a turn at that speed and turn radius, you're in a skid. The other way would be to bounce a light beam off the pavement and use sophisticated measuring techniques. I don't know how it works, but a device like this is used to test cars. For instance, Car & Driver magazine uses this device rather than the car's speedometer when publishing a car's maximum speed. -Matt

Matthew Mucker <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> wrote: > The way I'd do it would probably use an accelerometer mouned > parallel to the rear axel. I'd then connect a sensor to the > steering mechanism. If the acellerometer detects lateral movement > and the steering wheel is pointed straight ahead, a skid is taking > place. Matt: Good idea. Unfortunately, the accelerometer won't "detect lateral movement" under the conditions stated in the problem (brakes locked up, car sliding on ice). The reason, of course, is that (if you disregard the very small drag vactor in the direction opposite that of the skid) there IS no acceleration under those conditions. This issue is related to the so-called "problem of the vertical" which Kurt Godel -- a brilliant mathematician who should have known better -- claimed would make inertial guidance of ICBMs impossible. -Andy Andrew Warren - fastfwdKILLspamix.netcom.com Fast Forward Engineering, Vista, California http://www.geocities.com/SiliconValley/2499

> Date: Sat, 11 Jan 1997 19:17:03 +0100 > Hello PICLIST > > My suggestion to solve this problem would be to use an ultrasonic > transducer, or preferably 2, pointed at an angle to the road, and together > with a pair of ultrasonic receivers utilize the Doppler-effect. > If it is made as a bridge, it should be possible to get a signal for even > very small movements. > Poul Bundgaard, If I understand your suggestion correctly, Poul, it will not work. At least, it will not work to the extent that the road can be modelled as being smooth. The reason is that, in order to produce Doppler shift, the distance between the source, reflection point and receiver in some direction must change with time. As I understand the geometry, the distance between the source, reflection point and receiver in all (or any) directions would be constant, even though, from the perspective of the source/receiver, the road would appear to be moving. Specifically, the road would appear to be displaced along itself as the vehicle moves. That is, if you draw a straight line to represent the surface of the road, the line (road) will slide along itself; there will be no displacement normal to the line (road). Hence, along any reflection path in a given direction from source to receiver, there will be no change of path length over time and, hence, no Doppler shift. I am assuming that both the source and receiver are mounted on the vehicle. On the other hand, if the road is not smooth and there are projections sticking upward from the road, they will result in reflection path lengths along a given direction that will change with time as the vehicle moves and will produce Doppler shift. Obviously, the "rougher" the surface the greater the effect. How rough is enough? As a rough (no pun intended) rule of thumb, the projections must be at least on the order of a wavelength in size before their Doppler shift can be "seen" reliably. If you were considering that the vehicle might be skidding because it was on smooth ice, it would be rather difficult to satisfy this wavelength requirement. --- Warren Davis ================================================ Davis Associates, Inc. 43 Holden Road West Newton, MA 02165 U.S.A. Tel: 617-244-1450 FAX: 617-964-4917 Visit our web site at: http://www.davis-inc.com ================================================

Tony's two cent$ If you can predict the expected G forces in a turn of given radius at a given speed.Can you not detect easily the absence of acceleration and assume you're skidding.What do you do then ? Warren F. Davis wrote: {Quote hidden}> > > Date: Sat, 11 Jan 1997 19:17:03 +0100 > > Hello PICLIST > > > > My suggestion to solve this problem would be to use an ultrasonic > > transducer, or preferably 2, pointed at an angle to the road, and together > > with a pair of ultrasonic receivers utilize the Doppler-effect. > > If it is made as a bridge, it should be possible to get a signal for even > > very small movements. > > > Poul Bundgaard, > > If I understand your suggestion correctly, Poul, it will not work. > At least, it will not work to the extent that the road can be > modelled as being smooth. The reason is that, in order to produce > Doppler shift, the distance between the source, reflection point and > receiver in some direction must change with time. As I understand > the geometry, the distance between the source, reflection point and > receiver in all (or any) directions would be constant, even though, from the > perspective of the source/receiver, the road would appear to be > moving. Specifically, the road would appear to be displaced along > itself as the vehicle moves. That is, if you draw a straight line to represent {Quote hidden}> the > surface of the road, the line (road) will slide along itself; there > will be no displacement normal to the line (road). Hence, along any > reflection path in a given direction from source to receiver, there > will be no change of path length over time and, hence, no Doppler > shift. I am assuming that both the source and receiver are mounted > on the vehicle. > > On the other hand, if the road is not smooth and there are > projections sticking upward from the road, they will result in > reflection path lengths along a given direction that will change with > time as the vehicle moves and will produce Doppler shift. Obviously, > the "rougher" the surface the greater the effect. How rough is > enough? As a rough (no pun intended) rule of thumb, the projections > must be at least on the order of a wavelength in size before their > Doppler shift can be "seen" reliably. If you were considering that > the vehicle might be skidding because it was on smooth ice, it would > be rather difficult to satisfy this wavelength requirement. > > --- Warren Davis > ================================================ > Davis Associates, Inc. > 43 Holden Road > West Newton, MA 02165 U.S.A. > > Tel: 617-244-1450 FAX: 617-964-4917 > Visit our web site at: http://www.davis-inc.com > ================================================