I would like to know what sensors/devices i can use to detect that the track has ended.
The end/finish of the track is the only part where there are no walls on all sides. Thus the device must go onto the platform and stop.
Some sort of optical sensor that can detect the wall.
A microswitch with a roller that runs along the wall and the wall keeps the switch pressed.
How far will your device be from the wall?
...R
That will not be possible as the track can have something similar as the attached image AND the robot will be around 30cm and the track is 1m width with 15m length
Hi,
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Ops diagram.
Tom... 
Hi,
So you need more than just to sense the end of the track, you need obstacle avoidance as well?
Tom...
No. 
The issue i have is how to detect that the track has finished. I have already researched for gap avoidance and collision which i have found solutions to.
Just use the same sensors you're already using for obstacle avoidance to also detect the end of the track. If they can detect a block and a gap then they can detect the lack of a wall and a gap on 3 sides of the track.
I was planning of doing 2 sensors at the bottom to look out for gaps and 2 sensor on top to detect that there are no obstacles at the front. What you are suggesting is to do 2 more sensors at the side of the robot to detect the 3 no walls?
lukik:
That will not be possible
I mentioned two options. Which one is not possible?
I remain of the opinion that both are possible as the wall seems to be continuous in the image attached to Reply #3 and displayed in Reply #4
By the way, see this Image Guide for posting images
...R
Robin2:
A microswitch with a roller that runs along the wall and the wall keeps the switch pressed.
The robot may fall if it keeps a hold of the wall.
Furthermore, as for the 1st option what type of optical sensor?
lukik:
The robot may fall if it keeps a hold of the wall.
I have been assuming that you would apply a little practical ingenuity.
Furthermore, as for the 1st option what type of optical sensor?
Likewise. have you looked through supplier catalogues.
Sonar is another option.
...R
Indeed you should be able to use the same sensors as you already use for your obstacle detection: add two that point sideways, and one of them should always see the wall. If no more wall, stop, as you're on the platform. The gap detectors should take care of that part, guiding you towards the platform part (as there's a gap on both sides), so when you don't detect a wall on either side it means you're on the platform. You may need to move a bit further forward of course to get off the track, but you then know exactly how much.
Yet another option: don't bother with detecting the wall. The moment you detect gaps all around you (resulting in a very narrow track), you can tell you're on the platform. Unless there are any parts of the track that have no obstacles and are no wider than this platform bit.