Quote:
Originally Posted by Ether
Are you suggesting that round-off errors using double precision floats cause instability if using RPM?
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Perhaps, wrong choice of words. Consider this: if the system can, in fact, go up to 1000 RPM, the initial error when starting up from rest is 1000 RPM. In order for you to get the appropriate output from -1 to 1, your P constant will need to be about 0.0001. Now, that is not accurate at all, but trying to demonstrate that the constant will need to be tiny. But if that same system was measured in FPS (You are using RPM to derive this, so it will be the same accuracy as measurement), you will only be getting FPS up to 14 FPS at most. You have less of a range to work with, so the P can be about 0.1 instead. I was just pointing that out because his picture showed the P to be 0.3, which is way too big for a system measured in RPM. Just tuning it would be easier and I doubt the round off will have much errors using doubles.
Of course, always check your inputs and outputs to be in range.