23 October, 2003
The morning's mission was to uncrate the 800 lb weighing sled and make sure it had survived its long trip from Fort Collins, Colorado to McMurdo, Antarctica. This was one of the better-constructed crates you may ever have to dismantle. Armed with pry bars and hammers, we spent an aerobic hour removing sides and top to reveal the gleaming white sled within.
This sled, built in Fort Collins, was designed by Darren after last year's field season. The sled that he had used was too cumbersome in the field-it's weight and the difficulty of setting it up to give accurate measurements kept him from collecting as much data as he would have liked for his mass dynamics project. This new sled was designed to be relatively lightweight yet strong, with a steel framework and aluminum weighing platform mounted on steel skis for ease of transport behind a pisten bully or snowmobile. Each of its 4 legs is adjustable using trailer jacks so that the scale can be leveled before use. The platform uses the same weighing mechanism that is used to weigh cattle. It has a digital readout that averages the weights received by the 4 corner-mounted sensors.
Once we had the sled out of the crate, it was time to calibrate the scale. The Crary Lab has a set of 16 metal weights, each weighing 56 lbs. Why 56 lbs, you might ask. I don't know-could it be because 56 is such an easy number to multiply in your head? Our first chore was to lug all the weights inside to a digital scale to make sure that they did, indeed, each weigh 56lbs. They were all within an ounce or so of the promised weight. Then we brought them back outside to the sled and put them on top of the weighing platform. Quickly now, do the math in your head, 16 x 56 = ? . Following along in the instruction manual, Darren set the scale to 896 lbs. Then, the fun began. We removed one weight, and the scale's readout was only 20 lbs less. We removed another weight and found that it was now 150 lbs less. Something was not right. So, it was time to take all the weights off the scale and try putting one on at a time. Okay, one 56 lb weight isŠ120 lbs. Add a second one and you getŠ150 lbs. Obviously, something was not working properly. We tried re-reading the instructions, re-calibrating the scale, and re-leveling the weighing sled. After much head-scratching and bewilderment we admitted defeat.
While the scale had been tested back in Fort Collins, it was apparent that there were definitely some differences in how it worked at 72F and how it worked at 5F. Science is about asking questions and developing hypotheses based on those questions. Was the problem mechanical or electrical? That was Darren's mission for the afternoon. The sled was moved to a heated workspace so he could spend the afternoon identifying and fixing the problem.
Calibrate the sled
Weights on, weights off, one more time
Why doesn't it work?
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