[bobcroucher]

Chain definitely stretches through wear, mostly the pins. Park Tools sells a chain stretch gauge for bike shops. The poor man's way is to measure 24 links at 0.5 inches each totals 12 inches when new. Once the chain reaches 12.25", it's time to buy a new chain. The stretched chain will wear out the aluminum chain rings and the rear cassette, and each costs more than a new chain. A new chain lasts 1000 - 2000 miles depending on cleanliness and lubrication.

Bike wheels are obviously much larger, so the chain life will be reduced accordingly. If we scaled 1500 miles down by 4 / 27, since 4 inches is a typical WCD wheel size, and 27 inches is a typical road bike diameter, you would get about 225 miles. That's still around 11,000 round trips down and back on the 52' field. The chain is quite unlikely to wear out based on revolutions alone. Work done to move each vehicle's mass is at least within a factor of 2, and would benefit the robot.

Robots don't get much road grime, and carpet fuzz isn't very abrasive, but they usually don't get much lubricant. The more lube you use, the more stuff sticks to the chain. By putting the chain in the tube, you can probably lubricate it a bit better without fear of contamination. I'm sure chains will typically last an entire season regardless. Putting the chain inside the frame tube probably helps protect it from game pieces and other robots as well.

According to Gates, a belt's stretch is nearly un-measurable over the lifetime of the belt.