Hello. I am beginning the process of taking a Century Swift 16 (a bit vintage but light and strong - about 550 rotor diameter) and converting it, with a Pixhawk, to an autonomous machine. I feel that this would be a good alternative to my quadcopter for certain applications.
Chief question, to start, does the GPS need to totally be out from under the rotor blade? This is a rather short coupled platform and I don't know if it would really be feasible.
I look forward to moving into the area of Arducopter and the traditional heli.
Thanks, Thor
Replies
The spinning heli blade itself doesn't cause GPS reception problems. On manned helis GPS works just fine. You can even do fixed integer work (centimeter level accuracy) with a GPS antenna under the blades of manned or unmanned helis. I've done it on both many times over the last two decades.
The issue on smaller unmanned vehicles, especially rotorcraft, is the close proximity of all kinds of electrical noise generators. This is what you want separation from, not the blades. Of course the smaller the craft, the harder it is to do.
Now you should always try to give your GPS antenna as clear a view of the sky as possible. Don't mount it right next to the rotor head if half way down the tailboom will also work equally as well. You just don't have to worry about getting out from under the blades.
It doesn't matter what the blades are made from. I have many thousands of flights with various GPS autopilots on ~800mm blade-size helis. Carbon fiber blades aren't a problem nor are lead weights in blades. The L1 GPS wavelength is 19 cm. Objects very near (but not completely covering) the antenna that aren't transparent to that frequency need to be roughly half that length or more across to start causing reception problems. Even a relatively wide cord 70mm blade doesn't get there. Even aluminum blades on manned craft which are wider than the L1 GPS frequency don't cause major issues since (hopefully) there's some space separating the blades from the antenna. Park a blade immediately on top of an antenna and there will be issues. Lift it up a meter or so and they dramatically reduce. Put the blades in motion and any issues are reduced even further.
Me thinks it might make a diff if the blades are Carbon Fiber or Fiberglass (cf or frp) and then it may make an even bigger difference if the GPS/compass were to be placed directly under the ubiquitius lead weights found in most if not all trad heli blades.
I'm interested to know which of these blades were in use by the posters here.
Thanks in advance
Dennis
My biggest hell uses 800mm carbon fiber blades. These are quite big but the only problem I have is when I stow the blades both over the top of the GPS. When the blades are extended and not parked over the GPS module, everything is fine Rock solid so far with dozens of flights and hours of air time. Most of that time was in GPS loiter or Auto mode.
I put the GPS as aft as practicable to get the compass away from the motor and esc, but still under the rotor disk.
45cm cables work and I don't feel the need to extend them further.
I have the GPS mounted under the main blades on all 3 of my machines, and have not noticed any specific problem with this setup.
Where are you guys finding cables long enough to run to the back of the tail? The longest I've seen is 45cm, which is not even long enough to put the GPS at the back of a 500 heli tail.
Thor,
In my opinion yes. I have had mine mounted both under the blades and on the end of the boom by the vertical fin. When the gps was mounted under the blades there were times when my satellite count would suddenly drop by 4 or 5. Also when reviewing the flight on mission planner it showed the heli 30 or 40 yds from were I knew it should be at times. Since moving the gps out from under the blades I have had no problems. I realize this is not a scientific answer, but, I believe it makes a difference.
Regards.
David Boulanger