Line Following Robot / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Line Following Robot

1 2 next

Move Thread

LAN_403

Michael W.

Sat Mar 04 2006, 06:03PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

Does anyone here have any experience with line following robots? or Does anyone have any good resources for construction?

c4r0

Sat Mar 04 2006, 06:06PM

Registered Member #151 Joined: Sun Feb 12 2006, 02:53PM
Location: Poland
Posts: 153

My brother built this kind of robot using LEGO RCX system ... but hmm, this is not the thing, is it?

Bjørn

Sat Mar 04 2006, 06:21PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

What kind of design do you want?

1. Discrete components like transistors.
2. Digital logic chips.
3. Microprocessors.

Michael W.

Sat Mar 04 2006, 06:36PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

I'm preferable going for the most fluid motion (not all jerky when tracking) but the most simple....Usually those two things don't go hand in hand....

Bjørn

Sat Mar 04 2006, 06:58PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

How do you define "most simple"?
Simplest build.
Fewest parts.
Fewest internal states.
Shortest development time.

I would personally have used a microcontroller for fluid motion because it is easy to experiment with different strategies. If you use discrete components you need to change the circuit all the time until you get it right.

Self Defenestrate

Sat Mar 04 2006, 07:28PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

This has been on my list for a while. Haven't gotten around to it though.

Sulaiman

Sat Mar 04 2006, 08:05PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

I helped my daughter construct a 'Cybot' from 'Real Robots' magazine.
It has line-following as one of it's modes.
Cybot steers 'jerkily' .. definately not smoothy,
The Cybot has a free 'castor' wheel
and two independantly powered driving/steering wheels.

In theory smooth control is practical, BUT
The motors/bridges are ON/OFF forward/reverse
which will always give 'jerky' movement,
so you will require variable-speed drive/steer motors
OR separate smoothly variable steering.
Even if the propulsion/steering of the Cybot was smooth the line-following would still be jerky as the line sensors (phototransistors)
are simple light/dark sensors so linear feedback gives jerky steering.
so you need a line sensor that not only gives an indication of left/right of line, but also by how much.
(unless you use a predictive computer)
If you have simple but fast sensors and stepper motors
the movement will still be 'jerky' but will appear smooth.

for Cybot site.

Hazmatt_(The Underdog)

Sun Mar 05 2006, 08:43PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

here

What I can tell you is .....programming it sucks!

This is an 8051 based system, with LDR's and LCD status display. These were the requirements imposed on the class by our instructor. I would never use an LDR because the light/shadow problem and its a big one! That's why you need lights to light the tape path. I would always recommend using an IR pair, but a lot of the instructors are behind the times.

Also beware that your two motors will not usually drive with the same speed/force. So you have to use a transistor to drive the motor anyway, but have to put a pot on the base lead and adjust the drive current so they make the thing go straight.

Mine was slow as sin, but passed the course. This included gaps, take-offs, nasty turns.
A friend of mine had his pass in I think under 1 minute. But he had multiple subroutines to check the status of the LDR's. So its doable, you just have to continuously check in your subroutines.

...

Mon Mar 06 2006, 12:15AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I have made several :) They are a classic programming challenge for the basicstamp2.

So, what do you plan to use, microprocessor, discrete logic, computer?

The simplest way is to take an ir led and photodiode/cds cell (you can use discrete ones or get a little module that has them both), and aim it down at the line. You power the led all of the time. You ground one side (the cathode if it is a semiconductor one), and connect the other side through a variable resistor (try 10k) to vdd. At the junction between the light sensor and the variable resistor you connect some type of gate that has hysteresis of some kind. Hook up an led to the output of the gate, and adjust the variable resistor until it lights when you are off the line and is off when you are on it (or vice verse if you used an inverter as the gate). Then build another receiver and adjust the same way. Then position them on either side of the line, so that when the car is on the line you have both leds on, and when it goes off one led goes out. Then you hook the output's of the sensors to a motor driver so that when it is centered on the line you have both motors going, but when one sensor touches the line it's motor goes off. To make it less jerky, you can make it so that when the moor would go off, it only slows down.

If you want to use a microprocessor look at the manual for the basic stamp 2, which uses a simple a/d converter to read the value of the sensor (using only a cds cell, a small cap, and 2 in/out pins), and some code to control it (which is very human readable, and should be easy to implement in any other computer/microprocessor system. The microprocessor version is a little harder to get sutup (make/buy the parts to use the uP), but will give you more freedom, and changing it's behavior is as easy as downloading new code. You can also use a single sensor (just ask), and integrate automatic compensation for changing light/etc.

Good luck!

stop4stuff

Mon Mar 06 2006, 07:13AM

Registered Member #64 Joined: Thu Feb 09 2006, 06:25AM
Location: Southampton, UK
Posts: 68

The Lego Mindstorms kits can acheive what you want. You get everything in one box, motors, sensors (light & touch). The RCX brick (the brains) has 3 sensor input and 3 motor outputs. Programming is done via a PC, and there's several firmware options to go for as well as the Lego firmware. It's possible to have a range of motor power settings, so motor control can be made quite smooth. You even get a layout on a paper sheet that has a line in an oval for bots to follow.

can you tell i like Lego :)

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob