How to incubate eggs?

Ok so i was outside with my friend passing a soccer ball and suddenly we see a squirrel knock a nest from a tree. We ran over to it and the eggs inside were unharmed so we went inside and watched the nest for 10 min but no mother. afraid the babies would die we took the nest inside but it in a plastic box with some paper towels a steaming hot paper towel thats wet and its over a heating pad. The only problem is that the heating pad shutts off every 20 min so at night the eggs would die. How can I make a SIMPLE incubator that works?