These trains were not toys, and they were detailed models, and they were built to try out ideas. For real trains. Best way to combine these incorrect sentences into one complete sentence.

The best way to combine these sentence into one correctly complete one is to use semicolon. In general, semicolon is used in order to combine two sentences that share similar idea into one. It is needed to avoid repetition and redundancy. So the correct sentence looks like this: These trains were not toys; they were detailed models built to try out ideas for real trains.