Thread: Discussion Brushless Coaxial Heli builds Using Vtail mixers View Single Post
Jan 26, 2012, 04:04 AM
OlliW
Joined Sep 2009
2,919 Posts
Quote:
 Now, what exactly is heading hold strength? or PID 1. What I mean is how does this value work?
oh, wau, that's a short but most though question. You can find billions of answers to this on the net from very basic to very advanced (but then unfortunately mostly incorrect, at least IMHO). What a "controversial" point this seems to be you can infer by e.g. peaking in cruzado's Free Firmware for GA250 project thread, and my point of view had be disputed (but it seems to yield results ). So, I honestly don't know how and what to answer. If you want a very detailed description of my understanding of the situation you may look at my Gyro Theory thread in the mini helis subforum. Otherwise, I can try to give a simple answer, but wouldn't hope it to be really useful.

First, it's PID I and not PID 1. I say that because this parameter is linked to one of the adjusting screws you find in the most popular and most widely used controller, the PID controller. The name derives from the fact that you have three parameters to adjust - yes, you're guessing right - these three are universally called the P-term, the I-term and the D-term. This notation in turn comes from what they are doing in controller language. the P-value adjusts the proportional part in the controller, the I-value the integrating part, and the D-value the differentiating part.

The P value is very often also called gain. In fact, what you know from your coax 3in1/4in1 as the gain poti, or for your gyro as the gain setting usually adjusted by the transmitter is nothing else this P.

The I-term is related to integrating. This means that you sum up your changes. In our case the gyro itself actually measures the yaw rate, that is the speed of rotation. Integrating the yaw rate tells by how much the heli has turned (I repeat, not how fast it turns but by how much it has turned), and gives you the current orientation of the heli, or the angle. This is quite similar to velocity and distance with your car. You have to integrate your velocity to know how far you have driven, i.e, where you currently are. Now, this may already be sufficient to see the main point. Knowing the integrated yaw rate, that is the actual orientation of the tail of the heli, the controller has a chance to control this orientation, which is what you know as heading hold. (how to get the controller to do this well is another story).

Hope this helps.