Quote:
Originally Posted by DW SD
I would be concerned about friction within the scisscors throwing off of the measured numbers. I know my old scissor lift had plenty of friction in the mechanism. In fact, it wouldn't drop, if it had no weight on it (though the setup itself weighed hundreds of pounds. I think your 5% measurement error assumes no friction or equivalent amongst all four. I don't think that is a safe assumption.
Can't you do something simpler and more accurate with a balance beam and maybe a spring with known force constant? Or maybe something with a known counterweight? How about something like the scales at the doctor's office?
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Definitely a concern - all those pins and links are going to add drag on the mechanism and skew the results. You may be able to calibrate such a setup, however, but the best system will be something with the fewest moving parts. I'd agree with DW SD - something like a simple balance beam supported on a single fulcrum would provide the least internal friction. Making that stout enough to support a car...that'd be a trick. Thinking of a commercial weight system, each wheel might rest on a pad that is supported on a load cell.