Frank,
Some tests you could do.
Good ideas. But I shouldn't do it all by myself, then there is nothing left for Dave and others to test
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Dave could measure the temperature with his IR camera, and/or tape a thermocouple on the case with kapton tape. I have only one sleeve left, don't want to break this. The packet is now shipped to the next tester. I have included another cute little toy I ordered from eBay and just got today and didn't test so far, would be interesting to see it in a video.
Thought about getting two and running side-by-side but then people might complain the trains aren't identical. So will run two tests and then edit side-by-side footage with timer. Maybe add a lap counter?
A lap counter would be nice. I thought about this, too, but didn't have much time, always crazy time at the end of the year with client projects. An easy way would be a photodiode, and then an Arduino which measures it on an analog input, and a simple software high pass filter and hold-off, no need for calibration. Outputs each lap time on the serial port.
Running two side-by-side is possible, just do two tests with four batteries, first test train A without sleeves, train B with sleeves, second test train A with sleeves and train B without sleeves, all in one shot. This should proof that there is not much difference. Then wait for a day so that the batteries can recover. Then a third test, using the two batteries from the tests without the sleeve: one in train A without the sleeve, one in train B with the sleeve. I guess the results will be really devastating for Batteroo. Don't forget to measure the open loop voltage of each battery at the beginning and the end of every test.
The number of tests for a significant result depends on the magnitude of the effect being measured. If the difference is something striking like 2:1, then only a couple of tests with a similar outcome is enough to start establishing confidence in the conclusion.
I'm pretty confident that the train tests are significant. I did now four tests, two with the sleeve and two without the sleeve, with two different battery brands. What I was thinking, after the second test you could argue that the train might have wear off, or getting dusty or something like this. But this is not valid anymore after the 4th test, and all tests are showing that with the Batteroo sleeves the time was significantly reduced, and the 4th test suggesting, that even the additional time for dead batteries with the sleeve is lower than without it (but maybe the train is running a bit faster for a very short time). Needs 6 tests as described above to compare all scenarios.