Interesting & worrisome finding - original GPS vs Mrobotic M8N

SPP · May 22, 2017

Hi guys,

I been wanting to do this ...LOL

Test parameters :

01. Place both my Solo on car roof and drive around a bit.

02. Solo #1 has the Mrobotics M8N and the Solo #2 is a back up Solo, virgin 100% everything original bought for parts. #2 gimbal already cannibalized ...he he he he.

03. Both Solos were allowed GPS warm up properly for approx 5 minutes, same spot prior to this test, which is just outside my garage.

04. While driving, I also record the screen of my Wifi Analyzer...holy cow, 2.4 Ghz is a pure MESS !!!!

.

Yes, people on the road think I am crazy...

When all done, I then playback at 1x speed the Tlog-s on MP, both at the same time and I sync as best as I can to the seconds and I screen record the Tlog playback.
.

I then convert both Tlogs to Google tracks KMZ.

CORRECTION : Red Track is Solo original GPS

.

So am I happy with M8N ? Not yet !!!
Watch the video below, pause and read well when new text appear. You will then understand my concern

NOTE : I will need to do some more test.
From this 1st test, I would not trust M8N in a very bad GPS signal area or lots of multipath signal, because
it may not tell me in time that the GPS lock is actually already lost and the Solo would drift so bad.

As I said, I need to do more test to make sure, why is this 1st test so slow* ( *as in NEVER ) in respect to 8MN
declaring GPS lost ?

======== WIFI CONGESTION ==============

The strongest signals are from the two Solo-s. Controller inside my car, on left seat. Me country a right hand drive. GP24577896 is my GoPro Session5 wifi.
Others are neighbouring wifi transmitters

.

Will continue...........max 10 images reached.

SPP · May 22, 2017

Wifi congestion continued.......

.

.

End of GPS test for now

pyrate · May 22, 2017

Not exactly sure what point you are trying to make.
That the original GPS was crap, that is a given
That the MRO is better but not solid? We know that its better, too many of us using it not to know. But is it perfect, no. Because the GPS is still way to close to the internal electronics on solo
The new Here is a properly designed M8N which should be better than the MRO, esp if you mount it outside solo and away from the internals.
I am flying a here on my DIY and so far it is quite impressive

SPP · May 22, 2017

PYRATE ASKED : Not exactly sure what point you are trying to make.
Watch the video, and please advice me why I am not getting GPS Fix lost indicated by M8N ?, which it already actually lost GPS fix like 10+ seconds. This is my worry. Other operational parameters, I like the M8N.

Original GPS is not very crappy, at least for my region. Slow cold start, yes.
I will show you something interesting during my comparison side by side warm up of both the GPS.
Give me time to edit the Mission Planner Tlog playback

pyrate · May 22, 2017

So again
the premise is that MRO M8N is losing fix but not reporting it?
That is a lot of data waiting for reason.
Good info but you might have led with what you were tying to represent

Maddog · May 22, 2017

Maybe GPS signals that close to the ground, on top of a metal car just ain't that great.
GPS was intended for aircraft in flight. (Real planes up high, away from virtually all sources of interference).

andrew.baker.142 · May 22, 2017

I haven't watched the video yet (at work), but you can be sure you are getting really bad multi-path interference sitting the Solos on top of your car at street level. The huge ground plane of you hood is not providing you a realistic testing environment.

SPP · May 22, 2017

Hi Guys,

Agree, I need to do more test, will remove the ground plane.

The one I want to verify is the moment my car went into my garage, where no GPS signal can enter in any decent strength to be useable.
Its a 3 storey building made of concrete.

The original GPS (7N ) did well by declaring GPS FIX LOSS within few seconds of my car parked deep inside the garage shielded
from GPS signal and HDOP becomes 100.

I am curious to why the 8M did not respond the same and instead for 37 seconds is still reading HDOP 0.9 and producing high error data points. I want it to declare GPS FIX LOSS

I have a few high sensitivity GPS units with Glonass capability too, but none will work in the garage.

I shall do more test, also with 2 other GPS loggers I own and the Solo-s, let see how it goes.
Will hand hold the 2 Solo-s from outside the road and enter the garage again

pyrate · May 22, 2017

SPP nice work and I am not dissing on you, but you may be overthinking

Pedals2Paddles · May 22, 2017

A few things.

1) You're over thinking this.

2) Multipath interference is why the GPS thinks it still has a decent signal. That's life. Not a sign of a bad GPS.

3) The total crap stock GPS has such a bad receiver, that it can't even receive the multipathed signals. Lol.

4) The pixhawk in the solo has clearly rejected the GPS signal as being bogus. All those prearm checks indicate it knows better. It would not use it.

5) The GPS itself can think it has a lock all it wants. The pixhawk doesn't use that indication. It is analyzing the position stability vs the compass and accelerometers. And that works correctly.

SPP · May 23, 2017

Thanks guys , the Pixhawk part is good to know.

Pedals2Paddles said:
5) The GPS itself can think it has a lock all it wants. The pixhawk doesn't use that indication. It is analyzing the position stability vs the compass and accelerometers. And that works correctly.

Indeed I am over thinking I guess

Since I did not actually fly the Solo-s, I sure hope what I see in Mission Planner playback for the GPS FIX respond, it does not represent 100% accurately what a Pixhawk will do when airborne. The GPS FIX thingy in semi indoor/multipath is scary, both GPS not only the original one.

pyrate · May 23, 2017

But kudos for thinking

Frank Foster · May 23, 2017

yea, kinda a neat experiment

RichWest · May 23, 2017

Like anything that communicates over the air, it's the antenna that becomes critical. Can't figure out why no one has upgraded the gps' patch antenna or at least spoken about doing so. I fly with plan A and V2 shield, other than delayed lock, it flies fine.

IIRC, it was being done on the P2's back in the day and showed improved results, $12 upgrade. I never performed the mod, so my knowledge is only second hand.

Peddles, your thoughts?

Pedals2Paddles · May 23, 2017

I have a crappy rev A in my primary solo. Without the v2 shield, it was virtually inoperative. With the v2 shield, it gets a lock fast every time, everywhere. But it's hover stability is still little drunk, which is to be expected of it because it is a crappy GPS. I don't think changing the antenna will change the performance problems it has. Those problems aren't because of a poor antenna. They're because of poor everything else about it.

An mRo will do better in all respects because it doesn't have those hardware issues. A here GPS will do even better in all respects. And an RTK will be like it's anchored to a pole.

SPP · May 24, 2017

I dont know what Rev number is on my #2 Solo, but my Solo #2 is the last inventory of the local 3DR distributor before they walk out of the business. Even my 1st Solo GPS is decent ( I put the plastic shield DIY ).
I guess being in the tropics I do get advantage of having better USA GPS sats presence & signal most of the time.

My #1 Solo using standard GPS hoovering accuracy is not bad at all, I would say 5 minutes within 60cm/2feet horizontal is possible. This is based on open sky. To me 2.5 meters accuracy in 30 minutes is already very very good. US Gov commits global average User Range Error of 7.8 meters 95% of the time.
I read that on May 11, 2016, the global average URE was ≤0.715 m (2.3 ft.), 95% of the time.
GPS.gov: GPS Accuracy

Long time ago between 2004 to 2009, 25 meters off on a next week is acceptable.
25 meters is the common "movement" of a small sunken bus used as FAD, which I used to dive every weekends. FAD = Fish Aggregating Device.

I have 2 of Mrobotic M8N board, so my Solo#1 get to try first.

A few test yesterday showed that my standard ublox7 GPS & Mro M8 warm start, the standard GPS only slower by 3 seconds or so, in a not so open sky. Its really that decent my standard ublox7 GPS, in my region.
As for position "drift" during the stationary test and not so open sky, both are decent.

For data point separation of my actual car track on the road lanes opposite travel, Mro M8 wins.

Surely MRo M8 is a good upgrade. In decent open sky it seems to do very well.
If one save smart move route and do the run again in say 1 hour, I am sure the MRo M8 repeatability will be better than the standard GPS. The short run I did showed standard ublox 7 GPS car track separations on my two way opposite run at average 0.6 meters spread while the Mro M8 showed average the more true 2.5 meters spread.

DavidPhillips · May 27, 2017

I installed the MRo but I also have the shielding from 3DR. I did not have a problem with the original setup other than taking a while to get lock.

wsalopek · May 27, 2017

Maddog said:
Maybe GPS signals that close to the ground, on top of a metal car just ain't that great.
GPS was intended for aircraft in flight. (Real planes up high, away from virtually all sources of interference).

Maddog...you make a good point...less interference is always better...but if what you are saying is , trueall of our ground-based GPS receivers wouldn't be working well. Our phones, car GPS devices, hikers, boaters, the list is quite long.

--

Bill

DavidPhillips · May 27, 2017

The radio from one may be interfering with the other. It's usually a bad idea to have them that close together. The controllers could also be a problem.

The original may indeed be better for your test conditions. It does not seem to be better when in normal use.

scriffij · May 27, 2017

Hobby grade GPS & GNSS have contained for some time (since SiRF III chipset from memory) a technology called canyon mode that tries to predict position when, as the technology suggests, you are at the bottom of canyon type situation and you don't have complete view of the entire sky (think inner city or even inside building). Canyon mode is only moderately accurate when there are other references that the GPS can use (previous accurate positions). Might I suggest that the 8MN is switching to its equivalent of canyon mode to continue to give positions (all be it not very accurate). As a rule if the GPS/GNSS cost less than a few thousand dollars it will be configured to try to give positions under as many environments as possible and be configured with settings to suite (elevation mask to 0 degrees, canyon mode set to on etc). where as survey grade GNSS are configured to give the most accurate position possible and therefore will not always give you a fix but when they do you know they are accurate every time (elevation mask set to 15/20 degrees, canyon mode off, L1/L2 multipath corrections set to high, atmospheric attenuation corrections, low pseudo range residuals small ambiguities between base station - most only possible with dual or triple frequency GNSS).
My 10 cents worth.... people are asking too much of a $20 piece of electronics that is only really meant for toys (which is how I treat my Solo - its a toy).