Project on Magnetic Tape following - AGV

[monty]

dear friends:

Hi !!

for our college project we have to make a magnetic tape following BOT.
it should be able to haul 100kgs from point A to point B.
we are at the mech. design stage. we have proposed the following:
2 independent servo powered rear wheels [100 Watt X 2] & 1 front wheel which
will have a steering mechanish to follow the magnetic tape.
Rear wheel will be as follows [2 sets] - wheel - pillow block - coupling - servo.
Is this workable ?? or anyone has better design options.
guidence will be appreciated.

monty

[superchiku]

wat do u mean by magnetic tape following bot.. ?? ..do u mean a black line.. can aservo drive such huge weight..? i didnt know..

better go for wheel chair motors...with appropriate motor controllers...

[SmAsH]

not black tape superchiku magnetic tape, its a tape that it magnetised, and servos can come in sizes that big but are expensive. wheel chair motors are a good suggestion but then you need a motor driver
and to monty, have you considered differential drive for this? also, what microcontroller are you using?
programming experience?
knowledge of electronics?

[superchiku]

i know the meaning of magnetic tape...but what do u mean by following a magnetic tape..

[SmAsH]

i know the meaning of magnetic tape...but what do u mean by following a magnetic tape..

he may be able to use something that picks up a magnetic field? or just use a normal line following robot, who can tell that its using the magnetic part anyways...

[ArcMan]

You don't need a steered wheel if you have two independently driven rear wheels (differential drive).  Just use a swivel caster for your third wheel.  In my experience 100W motors may be a little small for a 100 kg load, but that depends on how quickly you want to be able to start and stop, surface, inclines, etc.  I think they would be fine for a slow bot on a hard flat surface.

Also, for my yard robot, which easily handles a 100 kg load (e.g. my fat butt), I used wheelchair motors and constructed the frame from 1 1/4" square steel tubing (0.083" wall thickness).

[monty]

YA; i guess  two independently driven rear wheels (differential drive) is a better idea; but will it not need somthing more stable than a swivel caster in front ??.
the tape is magnetic guide tape - on the AGV a guide sensor is mounted on front which gives a signal of analog singal corrosponding to the deviation from centre of tape. more later

[ArcMan]

I'm not sure I know what you mean.  More stable?  What is unstable about a swivel caster?  Because it swivels?  It needs to swivel so that it will align to the direction that the differential drive is taking it.  I used two swivel casters for my yard robot, but that was for rough terrain, and I need to keep my mower deck level.  I don't recommend 2 swivel casters for flat smooth terrain because one wheel could be left hanging in the air if your frame is rigid.

An analog off-center sensor is good.  You can use PID control to follow the line.  I recently did this for my line-following maze robot.

[gamefreak]

Well if you are going at a considerable speed then a three wheeled vehicle could end up falling over. Then again, wheel chairs aren't the fastest things in the world and I have yet to see a swivel wheel tip over when trailing.

[monty]

dear all:

thanks for advice, PID control can be implemented with
analogue output of magnetic tape. which controller you
suggest to take care of all I/O in such a case. And
is there any algorithim available to care of this control.

monty

[ArcMan]

Almost any microcontroller with analog inputs can be used to perform PID control.  Folks on this group mostly use AVRs and PICs.  I'm a PIC guy myself.  I recently implemented PID line-following control on a PIC 18F programmed in C.  Took 3rd place in a contest with it, too 

[monty]

dear arcman:

you seem to be doing good with prizes and all.

is this ok - PIC18F1220- what other periferal devices will be
needed along with this.

monty

[SmAsH]

do you want to know what will be needed in full? like parts?

[ArcMan]

dear arcman:

you seem to be doing good with prizes and all.

is this ok - PIC18F1220- what other periferal devices will be
needed along with this.

monty

Actually, not a great choice.  I would go with something like a 16F876A for this job.  It has analog inputs for your sensor and couple of ways to command a motor drive (serial, PWM), and more I/O points for other sensors.
At a minimum, you need the sensor (which you have), a microcontroller, a motor drive and motors/gears/wheels.

[zai_jnr]

MOnty,

What the progress your project right now?

[mukeshtalks]

Hello Monty,

nice project you are doing. Can you help me out to let me know how to detect magnetic field by using which kind of sensor and what kind of tape you are using. from where i can get this sensor and tape.

regards
mukesh

[monty]

dear all:

can u help me - how to implement PID control for this BOT.

monty