Carbon fiber props and interference

Justgregg · Dec 20, 2015

I would stay away from carbom fiber props. Im sure If they have an advantage, DJI would install them on all the phantoms.

alokbhargava · Dec 20, 2015

Wibble said:
The satellite signals do not all come down vertically! Some are bound to come through the arc of the props. If the props reflect GPS signals it could cause problems.

I don't agree with your theory. They appear to form 4 discs but in reality most of the space is open to sky in time frame. I feel like laughing at the discussion. If you are not convinced, direct two laser beams on to the top of the P3 from different angles when props are rotating, show me a place where laser beams can't reach the top of the p3. And in reality, GPS signals are not just one or two sharp beams, they are spread all over.

I use DJI cf props and never had any issue.

Litz · Dec 20, 2015

Stick with the DJI brand everywhere you can. Had you crashed with the aftermarket props you'd have a MUCH more difficult time making a warranty claim. Aside from a gimbal guard (DJI doesn't make one) I stick to their brand, and have had 2 warranty issues resolved without any issue. Good luck, and happy flying!

alokbhargava · Dec 20, 2015

Daniel Voyer said:
Great discovery. I was going to get some DJI CF props mostly for the colour. But now I'll pass. Thanks

Don't just get confused by the appearance in the above picture, it's safe to use DJI cf props.

Wibble · Dec 20, 2015

alokbhargava said:
I don't agree with your theory. They appear to form 4 discs but in reality most of the space is open to sky in time frame. I feel like laughing at the discussion. If you are not convinced, direct a laser beam on to the top of the P3 from different angles when props are rotating, show me a place where laser beam can't reach the top of the p3. And in reality, GPS signals are not a sharp beam, they are spread all over.

I use DJI cf props and never had any issue.

Laugh away!
Ever heard of multipath interference?
Windfarms have been known to cause scatter which effects radar and gps signals amongst others.
I am NOT saying this is the cause - just a slim possibility. I always try to keep an open mind and not laugh at other people's ideas.

alokbhargava · Dec 20, 2015

Wibble said:
Laugh away!
Ever heard of multipath interference?
Windfarms have been known to cause scatter which effects radar and gps signals amongst others.
I am NOT saying this is the cause - just a slim possibility. I always try to keep an open mind and not laugh at other people's ideas.

Sorry if I hurt your feelings but I had a real big smile when I read it. Didn't laugh at you, laughed at the analogy being proposed.

There is not even a slightest possibility that rotating props will block GPS signals.

It's a human nature that we use our experience to correlate events but sometimes our basis go tangentially out. I do also get carried away with my experiences many a times.

Wibble · Dec 20, 2015

Block might have been the wrong word - interfere? YES possible!

alokbhargava · Dec 20, 2015

GPS signals are not sort of continuous signals that if we miss one packet of information, we lost the continuity. They contain discreet information. GPS receiver collects info from different satellites at any time and tries to compute geo coordinates and time using multiple triangulation technique.

Data is correctly received or not received are the two states. That's why I used a term blocking. Interference is mainly a phenomenon in analog world where values get distorted.

Sorry, we are moving away from the main topic....

Wibble · Dec 20, 2015

Did you know the GPS signal is analogue?

Shammyh · Dec 20, 2015

And what's makes anyone think a spinning propeller would affect the GPS signal anyway?

The signal makes it 12,500 miles from space, through our atmosphere, and it's stopped by a couple millimeters of plastic? No doubt it attenuates the signal some small amount, but the spinning has nothing at all to do with it. In fact, the spinning reduces the amount of time that the propeller is in the path of the signal. Look at the shadow behind a fan. Does the shadow appears at all to be "blown" by the movement of the blades?

GPS signal = radio waves = light.

In addition, the GPS itself is doing tons of calculations and taking into account multi-path all sorts of other interference. And it does a pretty good job too. My P3P with dji CRP props is absolutely stable at hover, without any VPS help. As is the same for countless others.

That all said....

1) This is a total red herring, and we should move on from this thread

2) Only use official DJI props

Chuck Young · Dec 20, 2015

Wibble said:
The satellite signals do not all come down vertically! Some are bound to come through the arc of the props. If the props reflect GPS signals it could cause problems.

Well Ok then.

Chuck Young · Dec 20, 2015

So here appears to be the spec sheet for the antenna or at least 1 very similar.

http://www.gpsinformation.org/joe/ga26ant.pdf

Picture of DJI antenna:

Meta4 · Dec 20, 2015

For anyone interested, it should be easy to test on the ground

Wibble · Dec 20, 2015

Shammyh said:
And what's makes anyone think a spinning propeller would affect the GPS signal anyway?

The signal makes it 12,500 miles from space, through our atmosphere, and it's stopped by a couple millimeters of plastic? No doubt it attenuates the signal some small amount, but the spinning has nothing at all to do with it. In fact, the spinning reduces the amount of time that the propeller is in the path of the signal. Look at the shadow behind a fan. Does the shadow appears at all to be "blown" by the movement of the blades?

GPS signal = radio waves = light.

In addition, the GPS itself is doing tons of calculations and taking into account multi-path all sorts of other interference. And it does a pretty good job too. My P3P with dji CRP props is absolutely stable at hover, without any VPS help. As is the same for countless others.

That all said....

1) This is a total red herring, and we should move on from this thread

2) Only use official DJI props

Well it gets stopped by a few microns of aluminium foil! Carbon fibre is not plastic it is also conductive like foil!
Light from the sun travels 93million miles but it still gets bent and refracted.

PhantomRX · Dec 21, 2015

All I use are carbon Fiber props. Absolutely no problem with them but then again had no problem with the plastic ones.

Wibble · Dec 21, 2015

Meta4 said:
For anyone interested, it should be easy to test on the ground

Maybe I will. Wrap the blades in foil to see if that causes a problem.

Wibble · Dec 21, 2015

Ok for people who laugh off theories without keeping an open mind. It is a known problem!

Measuring the Effect of Helicopter Rotors on GPS Reception
Article Abstract

For instance
,
when a GNSS receiver is placed near rotating bodies
,
the signal undergo complex and non-stationary effects
called Rotor Blade Modulation (RBM).

Boebe · Dec 21, 2015

tcope said:
What information do you have to support this claim? Testing would show that there is no gain with CF props. DJI states the same.

In my RC airplane time I used wooden props, because you could see the nylon ones bend while adjusting the carburator. With high power engines nylon props could even break under load, and I have seen that often. I don't have my rpm meter anymore, but I guess that the props on a Phantom spin rather fast. So imo the nylon props bend and twist under load and therefore there efficiency reduces.
I don't have any problems with my cf props. Use whatever you are comfortable with.
DJI states a lot. If all they states was true I was a more happy man, and there was no need for a excellent forum like this one.

steves · Dec 21, 2015

Well, thank you for all of your input. But as I said in the beginning of the post I'm not sure that it has anything to do with GPS. I think it has something to do with throwing the IMU settings off. They are after market products and I have no idea if carbon fiber materials are different in anyway. Such as being just reinforced or totally carbon fiber. I'm wondering if since they are conductive the rapid spinning could create some kind of magnetic field that would throw off the IMU. Please let me know if this makes sense to anyone.

Thanks again