What sensors can/should I get for redundancy?

I’ve seen some more modern than my Pixhawk1 flight controllers which use redundant GPS’s and redundant compasses. This sounds like a good idea for safety as well as increasing flight precision. Is this something I can do with my Pixhawk1? Should I?

I went ahead and ordered a Neo-M8n Ublox based gps unit and compass. I ordered the absolute cheapest I could find: about $15 and another $3 to hold it to the drone. For five bucks more, I could’ve gotten a cool looking one with cool led lights and a brand name but… That’s one of my priorities of the build is doing it as cheaply as possible, while still running great components. The internal quality looks good, reviews are good, So I feel fine saving a few bucks on it with cheaper looking components. I did the same on my Mauch power module and BEC’s; saved a few bucks by not buying the newer fancier looking and modular ones and kind of how I am doing throughout s1000.

Still too cold for autotuning here in the desert… I can only imagine the flying situation in Montana at the moment.

I’m absoluly in love with the hex core board and the cube


It took my a while to figure out why you posted about the Hex board using the cube… Heated sensors! :). Although I like the idea of using the original Pixhawk and all new surrounding electronics… I like the idea of autotuning without either driving to Texas or waiting until March more. I suppose I need to decide between the black, blue, or orange cube now.

I like that everything is together in one board, easy to setup and compact.
Autotuning is very easy to do these days, so do one when it’s cold and then another time when it’s warm… Takes only some minutes once u got the work flow.
I’m always using the black one, never tried another one. Never had any trouble with it.

The redundant sensors is what I am looking for, but the fact that they’re also heated is a major bonus. It’s on my list. I’ll probably go with the standard black, but thinking what the benefits of the orange would be. It doesn’t cost a whole lot more, but then again, the black is tried and true.

Theire was one YouTube video about all the differences…
But in the end, most people use the Black I recon

Orange is the new black.

The only difference between black and orange is the processor - orange uses the faster h7 processor. With the release of 4.0 - orange cube officially went from beta to released.

Blue is identical to black, but manufactured in USA for end users that need to source domestically.

Yellow is all but forgotten because orange is more powerful.

Red is supposedly a future product

Purple only has one IMU. Intended for ground vehicles because no redundancy.

Green runs 5v pwm signals specific to the 3DR solo quad copter.

The orange has built in ADSB… Something I was wondering about getting within the next 4 years anyway. Makes the decision easy. And a bargain at $250.

I assume I just flash it with copter version 4+ and load my params over and modify any new settings. I’m pretty sure I have all the cabling I’ll need or that it doesn’t come with. Will look cool with the orange color.

I’ll just pitch in my two cents here, I think we’ve got a great year ahead of us because of these three advances in the hardware space:

  • The faster H7 processors (on the Holybro Durandal and CubeOrange) are really huge upgrades in CPU power and memory. I think it’s 5x more of each. I hear other vendors will start selling ArduPilot compatible H7 based autopilots soon too. This makes life easier for the developers of lua scripting, object avoidance, and non-GPS navigation.
  • The new IMUs on these boards also have twice the range (30G as opposed to 16G) which will make them more resilient to high vibrations
  • The uBlox F9 GPS brings a large improvement in accuracy even if you’re not using the RTK features of the GPS

I didn’t even know about the F9 gps or the better vibration resistance. Both will be appreciated. I found some good information about the F9: New uBlox F9 GPS test & quick comparison to M8 series

I wonder how well the F9 rejects attempts to bring the copter down by using gps interruption devices. I saw that the M8n series of gps’s has some countermeasures built in, and thinking the F9 probably does too. Either way, I’ll be glad to have both.

Hi everyone,

Could someone please clarify the topic of compass “redundancy”.
So far what I know:

  • It is possible to mount and read up to three compasses (e.g. 1 internal and 2 external(Here2 GPS))
  • Only one compass is used in EKF (–> No sensor fusion on compass)

Therefore what I would like to know:

  • Is it possible to switch compass inflight automatically due to failure (total lost of one compass) or due to faulty measurements (bad data)
  • How is this being achieved?

If this is not possible, why is it called “Redudancy”? And why it is stated in EKF2 description:

EKF2 Advantages:

It can switch between magnetometers if there is fault

Thank you for your help and your clarifications

compass redundacy i believe is useless…is not needed to fly, only pointed the front in the desired direction, if this is critical for you then yes, but a compass failure does not cause a crash or control loss

After a discussion with @tridge, both the EKF2 and EKF3 have the same compass failover logic. They will switch when the main compass fails or if the innovations get too high (an “innovation” is the difference between the actual and expected compass values).

Hope that helps…

Thank you two for your help.
Indeed the heading angle is not needed to fly. But if there are already two GPS installed with two magnetometer, it would be nice to also use magnetometer redundancy.

Ok, I’ll try this out and do some further tests. The last time I removed one of the two GPS/mags completelety. However, it just appeared a message which said something like bad compass. And it did not recover (to the second).

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Of course you get “bad compass health” if you remove a mag and don’t recalibrate.
There’s a thing called compass order. I2C offboard mags are always 1st and 2nd (if you have two) and internal gets the 3rd position. And offsets are saved for MAG1, MAG2 and MAG3 upon calibration. When you remove an external mag, the internal switches to MAG2 position and inherits the former no2 offsets, which are obviously wrong.

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Hey ThePara,

Thank you for your help. However, this is not 100% true, because it is possible to fully deactivate the internal compasses, sucht that they are not in MAG1 or MAG2. This can be achieved by deactivating the corresponding drivers. This is what I did in my configuration and MAG1 and 2 are the externals and 3 doesn’t exist.

There is essentially no real defense against jamming or spoofing provided by the GPS receivers themselves. uBlox does have a “jamming indicator,” but long story short, it’s not really usable.

The only way to keep position hold capability in the face of GPS failure or interference is another position estimation system. Optical flow is the only real option here except external beacons or position cameras.

Currently, ArduPilot can (usually) handle a GPS outage and safely switch over to Optiflow, although there are still improvements being made.

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GPS L1 is at 1.5 GHz, L2 is at 1.2 GHz. If you’d consider the case of a lunatic going on a rampage to swat drones out of the skies, then yeah, having a F9P would help.

I have been asked if I could devise an anti-UAV tool for the 2022 World Football Cup (Soccer for our US chaps :slight_smile: ) and back then the F9P wasn’t comercially available and I didn’t fathom L2 into the equation. I didn’t pursue the opportunity, and it remained just an ideea, but given government lag in adopting to new technology, I’d say having L2 capability will jam-proof your copter for a couple more years, at least.

Hi rmackay9

I’m sorry bothering you with ekf compass questions.
I was just wondering, if the switching between two compasses is dependent on their innovations, shouldn’t it be possible to see or visualise these innovations.
I know there exists within the NKF3 tab the IMX IMY and IMZ. But I assume these are the innovations between primary compass and the first IMU (NKF8 for IMU2 respectively). Therefore, I would expect that there should somewhere exist the innovations of IMU1 or 2 with the 2nd compass.

Or is it like the first EKF core is using mag 1 and IMU1, second EKF core using mag 2 and IMU2, third EKF core using mag3 and IMU3. And in case of a Mag error, the ekf core is switched (EDIT: This seems less the case. I just checked the MI parametr of the first and second EKF core and they are both set to 0. Which means the primary mag is used)?

Thank your for your reply.
Kind regards