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There are quite a few methods of making good tracks for a tank. There is a good review of the subject in Bert Love's book, the Meccano Constructors Guide
I am presently finishing work on a BackHoe excavator, and the over-riding consideration was trouble free smooth operation and a prototype speed.
The largest track I have ever seen in Meccano was constructed from 4 1 2" flat girders, and this was the Dutch crane, lavishly and beautifully illustrated in CQ a few months ago. I had correspondence with the builder, Peter Jonges of Apeldoorn, and also others who I have met at exhibitions at Skegness and Henley. The best Meccano Tank builder in the world is McDonald, who's models are quite superb. Strictly to scale and very reliable. He uses Meccano flat girders, which are fixed to two bicycyle chains on each track, and the links are connected with 4BA screws and locktite nuts (of the type we discussed on Spanner some months ago). The chains on each track run round two bicycle sprockets at one end, wedged between two wheel flanges. It is not the purists method, but it works very well.
Meccano track is usually built up from flat girders, to which are bolted two double brackets centrally. The tracks are linked to each other by fish plates. It uses lots of 2 1/2" rods and collars and is expensive and heavy. I have seen successful use of various types of wheels including the face plate (part 109), and also none standard parts like Marklin. The problem with them is that the fish plate and double bracket chain rides up onto them. I just could not get it to work when I tried it.
I had a close look at Henley tracked models. Two experts on the subject are Tony Rednall, and Merv Wood. Both of them have built BackHoes. They both use a non-Meccano but a similar highly reliable method. Using the purely Meccano track I have described, they fabricate a sprocket from Teflon. The size will depend on the scale you use, but if it is 2 1/2" width track, then you will need a 15 tooth gear, and this is wedged between two wheel flanges (part 137), on which the links run. The idler is also wedged between wheel flanges, and is just a Teflon disc slightly larger in diameter than the discs on each side. It is very important to be able adjust the tension of the track, which should run on idlers to take the weight of the model. Well this runs very smoothly, and is quite trouble free. I have used an Escap motor (which Spanner discussed recently) for each track, and it is quiet and extra-ordinarily powerful.
Take a look at McDonald's extraordinary model building ability. He is an expert at military vehicles in Meccano.
Finally, take a look at this wonderful track layout designed by Roger Hill. The plans are available by request, and it just begs for a proper superstructure to be built for it. Who can resist the challenge of doing so, or to get two small motors into the base to drive it?
Michael Adler