Graupner R700 FM receiver – get the PPM signal

This must have already been discussed on plenty of other forums, but here I am, I want to use my Graupner FM transmitter / receiver with my quadcopter.

As Jordi from DIY Drones says “Intercept the PPM signal is the best way to obtain all the channels from any receiver, for a lot of reasons. The first one is performance, and the second is the simplicity (in code =P).”

First of all, here’s a quite useful diagram that explains well how the PPM works, and the relationship between this signal and the individual channels:

RC Receiver Timing Diagram

The Graupner/JR R700 FM receiver is quite easy to hack.

Quadcopter – home made

29 Mar 2011 – V2 is here !

Latest and greatest version, not that light but not too heavy either...

Quadcopter V2

Now I know it was all useless, but until 2 days ago, I still thought the only problem with my quad was the frame/motors and the huge vibrations they generated…

2 days ago, on Sunday night, I finally had the courage to face the truth : it could be my fault, it could be my code ! 🙂

Actually while looking at the http://www.multiwii.com/ site (huge thanks Alexandre, and really great stuff !!!) it occurred to me that their code should support my configuration out of the box.

To be honest, I’ve always though that it might be a problem with my code, but the only options to check this would have been:

1. buy an ardupilot or some other verified system and install it
2. modify the ardupilot or some other verified code to make it run on my configuration

None of the above options were easy and they could have introduced new problems by themselves…

But the multiwii code, looked like it should work with barely a few lines of change !!!

And indeed it WORKS ! Or at least it balances muuuuch more steadily on 1 axis !

This seems to prove that while I do have quite a lot of vibrations they don’t stop the quad from flying.

I still don’t know what the exact problem was with my code, I will have a look into the details once I manage to fly for real with the new code…

Motor vibrations

No motors running, just "natural" noise of the sensors...

This post is obviously related to my “roman-fleuve” post about my attempt at building a quadcopter… I’ve decided however to create a new post as the initial one has already become too long, and dealing with vibrations is a more general mechanical question, that applies to much more than just quadcopters.

I still don’t know why my quadcopter refuses to balance properly, and to be honest it could be anything: the frame, the motors, the ESCs, the code, literally ANYTHING !

However, I have the feeling it’s related to vibrations, and there’s only one way to find out: done with the funny part of building the quad, now enters the tedious/annoying task of setting a vibrations test bench and do some measurements…