Hello,
I'm working on a project where we are building a collision avoidance system using IR sensors and stereo vision from cameras. Part of my contribution to this project involves moving the quadcopter in response to an object that our copter "sees", either through our camera, or with our IR sensors.
The quadcopter testing platform we are using is the 3DR IRIS+, and that uses the Pixhawk autopilot which does have an RC receiver input (which is in the PPM
The only problem is, I haven't found enough good documentation about the PPM signal that can characterize the electrical properties well enough (what are the logic voltage levels, what is the maximum period, etc.) I have a receiver for the copter, but I do not have any matching transmitter that was provided for me. I am going to look up the model number of the receiver that we do have and post it later today.
So the question is: How does the PPM signal look like if we were going to simulate one for input into a Pixhawk autopilot? And can we simulate a PPM signal into the autopilot to tell the copter to move left, without having to mess with any sort of PID controller?
For reference, the microcontroller I'm using is a PIC32MZ (2048ECG064). We don't have enough time now for a redesign with an easier chip to use. I know the chip is hard to use.
Replies
If you're trying to simulate a ppm signal to the autopilot, the pixhawk is designed to accept a wide variety of ppm signals, any ppm generation library should be fine.
In terms of your project, what are you trying to do? You want to control the copter according to your sensors WITHOUT some sort of PID controller? If you don't have a robust flight controller for this autonomous response that sounds like recipe for disaster. Is the system supposed to simply interrupt a manually controlling pilot? If that's the case then you shouldn't simulate a ppm signal to adjust control, you should program that response directly into the autopilot.
We're trying to simulate a remote control signal from our collision avoidance board. For example, if you have a remote control and you have the right stick set up so that pushing back on the stick causes the copter to move in reverse, we intend to do just that.
Our test will be with the quadcopter in a stationary position, hovering above the ground. From there, we will have 2 forward-facing cameras and some IR sensors around the body of the copter. We will approach the quadcopter with a detectable object (a simple shape for the scope of this project) and it will move in reverse if the object is detected to be too close.
I should clarify, this is a project for a senior design course. Our TA is working in a group where they are still working on directly interfacing with the code of the Pixhawk autopilot to implement some tilt-rotor flight system.
Ok, so it looks like our receiver spits out an active low CPPM (summation of PWM) signal with a period of 18ms and a logical voltage of 3.3v.
For anyone wondering, our receiver is a FrSKY D4R-II 2.4GHz receiver.