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PID Control Challenges

janismac.github.io

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Re: PID Control Challenges

#31

Post by goku12 »

bandrami wrote: post #20

My control systems prof said every engineer has done an inverted pendulum problem in school and nobody in their career has ever been asked to balance an inverted pendulum. So our final was a thermostat instead.

An unstable rocket (almost all of the big ones) is an inverted pendulum of sorts. The combined center of thrust and aerodynamic forces is usually below the C.G, and the rocket tends to tip over if not actively stabilized. To add a little, a slight margin of tipping is allowed, but the rocket tends to break up if the angle of attack crosses certain limit at high speeds.

Re: PID Control Challenges

#33

Post by goku12 »

galangalalgol wrote: post #9
stefan_ wrote: post #7

Earlier quoted context omitted.

It's a nice theoretical implementation but few practical examples would be found using floating-point math, running as they are on systems that don't support it.

Is this still true? It seems like most IoT stuff has chips that easily eclipse the capabilities of my Amiga1000 and are 32bitbwith hardware floats. Looking around, I'm having trouble finding something that isn't a 32bitHF in my house. Possibly my Keurig machine? Even using digital instead of an RLC implementation in a coffee machine seems like a waste, but I'm old.

Even if you could, floating point may not be the best representation for control applications. There are a lot of problems, like NaN, as somebody pointed out. Even neglecting that, a fixed point representation may be better.

You don't need the fine precision or large range that floats have (we get those using exponents). Signal variations below a certain threshold are drowned out by the noise floor. Signals in control systems also have an expected maximum bound.

At other end, stability calculations based on quantization noise may be difficult with floats, since their least count changes with exponent. Fixed points have a uniform LC throughout its range.

Re: PID Control Challenges

#38

Post by sho_hn »

ghotli wrote: post #25
Philpax wrote: post #8

Earlier quoted context omitted.

Not all PID controllers are destined for embedded. They’re quite useful in gamedev, for example.

If you're willing to expand on this, color me interested.

I encountered an example recently in a Star Citizen changelog entry about the PID controller governing the interaction of an NPC character pushing a trolley, and tuning the constants for it.

My reaction was a similar "Huh - makes sense".

Re: PID Control Challenges

#40

Post by benreesman »

An “obvious in hindsight” (I missed it) application of control theory in general and PID controllers in particular is exploring more of a corpus when the fleet is less loaded in an IR setting.

@ajtulloch might be the world’s leading expert in making 100 billion bucks in 2 months with a device that can be built out of mechanical parts.

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