Hello, getting into this hobby really explode my brain, since there're way too many information getting into your head.
(and people without basic science and computer knowledge like me

The question is, the number of PIDs are proportions or like exact numbers of how much force the quad will react to "errors" ?

have 2 210mm quads, tuned it and feel pretty good
and I'm wondering if the numbers in PIDs are similar on 130mm quads. If so i can get a better ground to tune my quad.

Thanks a lot for reading this dumb question

There are no dumb questions, only dumb answers. The most simple answer is, PIDs are relative and depend on a lot of things.

One thing you have to have in mind is power to weight ratio. Of course there are lots of things playing into this aside from raw motor/battery power, for example prop weight / prop load (a lighter prop will react much faster to the FC's request to deliver power).

Another thing is frame size. While a larger frame will naturally be slower to react (for example when starting a roll) due to higher weight/inertia, the longer arms act like a lever - it does not need more power to reach a certain rotation rate, or to hold a certain attitude.

The most special thing to look at is yaw though. The closer the motors are to the center of the quad, the higher the effect of direct momentum exchange will be. The larger the quad is, the more yaw performance will suffer. At least in my experience, smaller quads generally need lower yaw P and are quick to spin, while large quads can really struggle to reach higher rates at all.

Aside from PIDs, also the optimal filter settings can be very different. Smaller props and higher kV will produce noise peaks at higher frequencies which means notch filters will have to be adjusted differently (if used at all).

Hope this helps as a very general overview.

oh that really explained a lot to me
Thanks!

After i built my first quad, the first hover was scary
it instant roll and flip like crazy, looks like too much P.

That scared my a lot and makes me don't trust the stock PID for a long time

PID tuning won't effect the speed at which your quad rolls. That was a misconception I had when I started, as well.

The PIDs are parameters that work in the background to smoothly change the quadcopters orientation when it is given an input. That means, when you give it an input, the PIDs influence how strongly the quad will react to that change, not how fast it will make the change. Kinda. . .

If the quadcopter was flipping like crazy, it's more likely a rate and expo setting that you want to change. What software are you running? Stock Betaflight rates are much higher than Cleanflight and toy quads, so that might be more what you want to look into. Right beside the PID tuning in the configurator, you will see "Rate" and "Super rate" options. You can decrease these to make the quad respond a little slower. As well, there will be a number (probably around 680 something) that represents the rotation speed. That number is degrees per second, so at 680, that's two full flips in one second. You can use that as a gauge for how much you want to change the rate settings.

As well, you will see an "Expo" option. This adds a bit of a curve to the inputs so that they are a little more sensitive around the centre. If you increase the Expo, the quad will behave smoother at the centre of the sticks, and still give full command at the endpoints.

I'm no expert at all but have definitely noticed I need far lower P gains on my high power to weight ratio rigs regardless of the size

(16-May-2017, 03:53 AM)fftunes Wrote: There are no dumb questions, only dumb answers. The most simple answer is, PIDs are relative and depend on a lot of things.

One thing you have to have in mind is power to weight ratio. Of course there are lots of things playing into this aside from raw motor/battery power, for example prop weight / prop load (a lighter prop will react much faster to the FC's request to deliver power).

Another thing is frame size. While a larger frame will naturally be slower to react (for example when starting a roll) due to higher weight/inertia, the longer arms act like a lever - it does not need more power to reach a certain rotation rate, or to hold a certain attitude.

The most special thing to look at is yaw though. The closer the motors are to the center of the quad, the higher the effect of direct momentum exchange will be. The larger the quad is, the more yaw performance will suffer. At least in my experience, smaller quads generally need lower yaw P and are quick to spin, while large quads can really struggle to reach higher rates at all.

Aside from PIDs, also the optimal filter settings can be very different. Smaller props and higher kV will produce noise peaks at higher frequencies which means notch filters will have to be adjusted differently (if used at all).

Hope this helps as a very general overview.

(16-May-2017, 06:14 PM)Drross Wrote: PID tuning won't effect the speed at which your quad rolls. That was a misconception I had when I started, as well.

The PIDs are parameters that work in the background to smoothly change the quadcopters orientation when it is given an input. That means, when you give it an input, the PIDs influence how strongly the quad will react to that change, not how fast it will make the change. Kinda. . .

If the quadcopter was flipping like crazy, it's more likely a rate and expo setting that you want to change. What software are you running? Stock Betaflight rates are much higher than Cleanflight and toy quads, so that might be more what you want to look into. Right beside the PID tuning in the configurator, you will see "Rate" and "Super rate" options.  You can decrease these to make the quad respond a little slower. As well, there will be a number (probably around 680 something) that represents the rotation speed. That number is degrees per second, so at 680, that's two full flips in one second. You can use that as a gauge for how much you want to change the rate settings.

As well, you will see an "Expo" option. This adds a bit of a curve to the inputs so that they are a little more sensitive around the centre. If you increase the Expo, the quad will behave smoother at the centre of the sticks, and still give full command at the endpoints.

 thanks for the reply
what i did was just hovering, and once it get over 1 feet it flip like crazy... then i just lower the P, it turns normal. Later I started learning tuning PIDs, and right now i can get the P on like 78-81 LOL

i was using something like BF 2.9 something

and I do know how to use rates and expo... just get confused a bit on throttle mid

(18-May-2017, 02:38 AM)DGworks Wrote: just get confused a bit on throttle mid

Throttle mid does nothing by itself. It only defines where throttle expo is applied. If throttle expo is zero, then throttle mid does nothing at all.