'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??
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.
At 12:25 10/01/97 PST, you wrote:
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
At 12.25 10-01-1997 PST, you wrote:
Med venlig hilsen / Best regards
Poul Bundgaard Phone +45 86 65 13 92
Pr¾stev¾nget 4 Fax +45 86 65 13 92
Denmark E-mail: vip.cybercity.dkp_bundgaard
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
Matthew Mucker <MITVMA.MIT.EDU> wrote: PICLIST
> 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
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.
Andrew Warren - ix.netcom.comfastfwd
Fast Forward Engineering, Vista, California
|> 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.
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
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:
Paul Bundgaard wrote:
> The alternative would be a gyroscope, but then we are talking money - mucho
Have you looked into the (aforementioned) laser gyros? They use them on
RC aircraft, and more specifically RC helicopters, all the time and should
be fairly inexpensive. Of course, as always with money, fairly
inexpensive is relative.
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