Author Topic: detecting peripheral objects at speed  (Read 4292 times)

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Offline tujTopic starter

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detecting peripheral objects at speed
« on: October 21, 2005, 10:53:03 AM »
(my apologies to anyone on Robogossip as this thread is cross-posted there)

 Hi guys.  I'm new to robotics, but not to programming or digital systems design.  I want to make a robot based on a RC car chassis that can guide itself through a series of cones.  So if I set up a path of cones that are spaced, say 10' apart, the robot will say between them.

My first, and thus biggest problem is how to detect the cones and determine their range from the robot.  I've considered ultrasonic sensors, lasers, and stereo cameras.  Each have their own drawbacks.  The basic requirements are:

-identify cones between 10 cm to 400 cm on either side of the vehicle.

-estimate the distance of each cone within 10 cm.

-identify cones at speeds up to 60 mph.

Each approach seems to have some problems.

Ultrasonic: limited range, although some systems claim to get to 4 meters or more.  Limited coverage arc; usually about 15 degrees.  Limited sampling frequency (usually 10 hz).

Lasers: too expensive

Stereo cameras: limited coverage arc, usually 65 degrees.  Limited sampling frequency; usually 30 hz.  More complex due to need for stereo processes (pixel correlation, triangulation, etc).  Need to have a second, identical camera in each sensor installation.

What do you guys think?  My biggest problem with the ultrasonic and camera systems are that their fields of view are too narrow to detect something passing laterally at 60 mph.  I've considered cross-directing the sensors (ie. the left-mounted sensor points across the vehicle to the right), but this has a number of negatives for my vehicle.  Ideally, my sensors are mounted at the same height as the wheels.

Offline Admin

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Re: detecting peripheral objects at speed
« Reply #1 on: November 04, 2005, 08:15:23 AM »
So why is your RC car going at 60mph?!?!? My first thought is, not possible to have a robot operate this fast. The DARPA Grand Challenge Robots could barely even go half that speed . . . So I will assume you meant perhaps 16mph max . . .

The main problem with a RC car chassis is that it is really small so you cant pack too much on it . . . but I have seen alot done with them, as well as I have tried to make a robot out of one in the past too.

Lets talk about sensors first. How much money do you have? I am assuming not much, so I will just tell you the cheapest way to go.
Sonar wont work cause they have really crap accuracy. Yes they can detect the cones . . . but with 10' spacing that just wont work.

My suggestion would be to use mono camera vision. Just a single low res RBG camera. Use the camera to detect the RED blobs of the cones. If the cone size is known, you do not need 3D camera vision as the location of the red blob in the image can tell you the X and Y coordinates. The size of the red blob in the image can also tell you the distance the object is away from the car. For example, a small red blob means it is far away. Simple size to distance math should give you a fairly accurate distance algorithm. I have done this in the past and it is really easy.

As for the camera . . . are you familiar with the CMUcam? I have used it successfully with many robots in the past . . . I am not recommending it as it is highly buggy and very not user friendly . . . but it can do the job super cheap.

O and just one last thing . . . cheap cameras detect infrared light (such as that emitted by the sun or certain indoor lightning) . . . it usually appears as the color red which can cause you problems. Either get an infrared filter lens for your camera, or spray your cones blue and detect that color instead . . .

Hope this helps . . .

Offline vash

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Re: detecting peripheral objects at speed
« Reply #2 on: December 18, 2006, 12:12:11 AM »
Patrao !!!!!!!

so hows ur robo shaping up.

Thing is i'm working on a demining robo and my main problem is obstacle detection like rock  etc.

So it would be great if you could help me .

looking for correspondence from you.



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