Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: kon on May 05, 2010, 06:35:14 AM

Title: distance
Post by: kon on May 05, 2010, 06:35:14 AM
How I can know the distance that the robot do without to know the radius of the wheel ?
Title: Re: distance
Post by: Cristi_Neagu on May 05, 2010, 06:42:52 AM
Hi

1. use a GPS
2. if you're having a hard time figuring out the diameter of the wheel, use an encoder placed on a smaller wheel of known radius; so, if your robot has four wheels, add a fifth wheel that would measure distance.
Title: Re: distance
Post by: amando96 on May 05, 2010, 06:43:19 AM
You can use optical encoders, measuring the dislocation of the floor, but it's too complicated, and requires a small CMOS camera.
That's how optical computer mice work.

Why can't you measure the size of the wheels?  ???
Title: Re: distance
Post by: Cristi_Neagu on May 05, 2010, 07:00:20 AM
Quote from: amando96 on May 05, 2010, 06:43:19 AM
Why can't you measure the size of the wheels?  ???

Maybe he's using inflatable tires, and the radius depends on pressure and load. Maybe not that important, but it might matter depending on the application.
Title: Re: distance
Post by: Soeren on May 05, 2010, 09:40:31 AM
Hi,

Quote from: amando96 on May 05, 2010, 06:43:19 AM
You can use optical encoders, measuring the dislocation of the floor, but it's too complicated, and requires a small CMOS camera.
That's how optical computer mice work.
Optical mice don't need to know the absolute distance and unless you run it on a ruler, it will be hard to tell the distance with any useable accuracy.
Title: Re: distance
Post by: corrado33 on May 05, 2010, 03:07:44 PM
Quote from: Cristi_Neagu on May 05, 2010, 06:42:52 AM
add a fifth wheel that would measure distance.

No one likes to be a fifth wheel...  ;) ;)

I'm thinking of implementing something to this effect on my bot.  Except mine's omnidirectional, so it'd be a caster rather than a wheel.
Title: Re: distance
Post by: Ro-Bot-X on May 05, 2010, 05:24:37 PM
if your robot uses 4 omnidirectional wheels, one on each side, like on a square, you can install encoders on 2 wheels that are at 90 degrees. Use one encoder for each direction of travel.

Use a washable marker and draw a small line on one wheel. Place the robot with the mark touching the floor near a ruler. Have the robot drive straight for 10 times the number of encoder pulses per one wheel rotation. Read the traveled distance on the ruler and divide it by 10 and you'll get your wheel circumference.
Title: Re: distance
Post by: corrado33 on May 05, 2010, 06:45:02 PM
Quote from: Ro-Bot-X on May 05, 2010, 05:24:37 PM
if your robot uses 4 omnidirectional wheels, one on each side, like on a square, you can install encoders on 2 wheels that are at 90 degrees. Use one encoder for each direction of travel.

Powered wheels slip, causing sensor drift.  A fifth non powered wheel would not slip (as much), therefore theoretically giving me better accuracy. 
Title: Re: distance
Post by: kon on May 07, 2010, 06:06:28 AM
What about technologies that used cameras ?
How they works ?
Title: Re: distance
Post by: Soeren on May 07, 2010, 10:29:42 AM
Hi,

Quote from: kon on May 07, 2010, 06:06:28 AM
What about technologies that used cameras ?
How they works ?
Not very well for dead reckoning.
Optical mice use a small camera (like 16 x 16 pixels).
Title: Re: distance
Post by: MikeK on May 07, 2010, 04:35:57 PM
How about ultrasonic distance measuring?
Title: Re: distance
Post by: Cristi_Neagu on May 07, 2010, 05:00:04 PM
Quote from: MikeK on May 07, 2010, 04:35:57 PM
How about ultrasonic distance measuring?

Measuring the distance to what?
Title: Re: distance
Post by: MikeK on May 07, 2010, 09:10:45 PM
Quote from: Cristi_Neagu on May 07, 2010, 05:00:04 PM
Measuring the distance to what?

If it's, say, a maze robot it could measure distance to a wall.  The OP didn't describe the situation very well, so I threw that out there.
Title: Re: distance
Post by: Cristi_Neagu on May 07, 2010, 11:05:18 PM
Quote from: MikeK on May 07, 2010, 09:10:45 PM
Quote from: Cristi_Neagu on May 07, 2010, 05:00:04 PM
Measuring the distance to what?

If it's, say, a maze robot it could measure distance to a wall.  The OP didn't describe the situation very well, so I threw that out there.

Yeah... that would work... So he can position the robot with respect to the wall in order to make a turn.
Title: Re: distance
Post by: kon on May 09, 2010, 09:25:25 AM
What about AI that used search trees ?
What about other sensors ?
How they can help ?
Title: Re: distance
Post by: MikeK on May 09, 2010, 08:16:18 PM
Smells like homework to me. :)