Will this work? - Alternative GPS

[gDallasK]

I have quite a lot of DJI bits and pieces and, having added a Phantom 2 body to my collection (with the original intention of transferring all my Phantom 1 internals to it to get more room for batteries) I now realise that - other than a set of ESCs I have most of the things I need to build another machine.

However, I don't have a spare "Phantom" GPS or compass (nor do I fancy spending £132 on buying them) but I do have a couple of spare GPS modules from DJI Flame Wheel kits. After taking one of the modules apart I was surprised to find that the circuit board holes were in exactly the right position to fit the lugs on the underside of the Phantom upper body. As you can see I have also used the lower part of the Naza housing to help secure the module in place and protect it from physical damage.

My plan is to equip my spare parts Phantom "SP" with a Naza V1 Flight controller, V2 LED (I know that will work) and a V2 PMU - obviating the need to incorporate the circuit board on which (normally) the Flight controller sits. I will use the standard ESCs - which I will need to buy (I like the LEDs). I also plan to use a Spektrum receiver so that I can control it with my DX8 transmitter. Most of this will sit on a carbon fibre platform occupied the space normally taken by the circuit board.

My major uncertainty however is whether or not the combined GPS / compass will work okay (since on a "real" Phantom the compass is mounted on the landing leg). Or is there a good reason to have it sitting atop a carbon fibre pole as it did when fitted to my old Flame Wheel?

Any advice on this plan would be very welcome.

 

[rilot]

DJI must have had a reason to put the compass on the leg. The inside of the Phantom's shell is pretty noisy with EM so I expect you're going to find you get all sorts of bad compass data.

 

[RogerClark]

I think the issue will be more than just interference to a GPS based compass

If the Naza firmware is setup to read compas data from a separate compass not compass data from the GPS input, the combined module won't work.


Probably the only way to know is to connect the GPS to the Naza and connect the Naza to a pc, then see if the compass readings are working.

If that does work, you can get over the interference by putting the GPS on a pole about 6 inches above the top of the phantom

 

[ElGuano]

The compass module feeds into the GPS on all phantoms but the p2, and there it's mixed on the mainboard as well, the puck will work fine.

A couple of points: +1 on interference, make sure you get the copper foam tape to isolate the puck from the rest of the phantom as best as you can, and don't let the Naza touch the tape, there is not a lot of clearance and the FC needs to be vibrationally isolated.

The phantom GPS has a saw filter, the Naza puck does not, this may result in more signal noise getting through to the GPS receiver when using the puck.

A few people replace the phantom GPS/compass with the Naza puck, most will stick it on a pole above the phantom shell so they don't have to worry about the noise. Is that an option for you?

 

[RogerClark]

@ElGuano

Just slightly off topic..

Is the mixed compass and GPS data on the P2 a standard format, that would work with a different FMU e.g. APM2.5 ?

As I'm thinking of swapping my Naza unit for an APM on my P2 so that I can have telemetry downlink , data recording and autonomous flight etc

Thanks.

 

[gDallasK]

The compass module feeds into the GPS on all phantoms but the p2, and there it's mixed on the mainboard as well, the puck will work fine.

A couple of points: +1 on interference, make sure you get the copper foam tape to isolate the puck from the rest of the phantom as best as you can, and don't let the Naza touch the tape, there is not a lot of clearance and the FC needs to be vibrationally isolated.

The phantom GPS has a saw filter, the Naza puck does not, this may result in more signal noise getting through to the GPS receiver when using the puck.

A few people replace the phantom GPS/compass with the Naza puck, most will stick it on a pole above the phantom shell so they don't have to worry about the noise. Is that an option for you?

Thanks for the tip about the copper foam tape - I'll certainly try that. So far as clearance is concerned, I'm planning to lower the mounting platform by a few millimetres to avoid any problems. It can easily be done by taking a Dremel and shortening the mounting posts. I've also just discovered that a spare upper platform from a Flame Wheel F450 exactly fits the Phantom - even as far as the curves matching the shape of the Phantom - so I won't need to spend time cutting a piece of carbon fibre to fit.

I don't particularly want to fit the GPS on a pole if I can avoid it. It won't do much for the looks of the Phantom.

 

[ElGuano]

Interesting, didn't know that about the f450 top frame. What are you going to do with that? You can't replace the main board with it...

 

[ElGuano]

@ElGuano

Just slightly off topic..

Is the mixed compass and GPS data on the P2 a standard format, that would work with a different FMU e.g. APM2.5 ?

As I'm thinking of swapping my Naza unit for an APM on my P2 so that I can have telemetry downlink , data recording and autonomous flight etc

Thanks.

That's a good question. I think it's not standard, since there are very specific hacks for the Naza gps serial coms; for flytrex, OSDs, telemetry etc. there's a community project to decode the gps data for Naza as well. I would think you wouldn't need any of that if it was just outputting some standard data.

 

[RogerClark]

thanks @ElGuano

I'm not too sure what "standard" is for these GPS units.

I just took a look at the UBLOX LEA-6H and it seems to support several protocols including NMEA and a proprietary UBLOX format etc.

I thought that the other dev's were looking at decoding the CAN bus, which contains a proprietary (non standard) where DJI have not released the specification / docs on the protocol.

But I guess the same could apply to their GPS

Personally, I don't know why DJI don't publish their CAN bus spec, I'd have thought it would lead to more sales rather than less, i.e the only reason I can see that DJI don't publish is in the hope that you have to buy certain components from them, but this will equally deter some people from buying a Phantom because its too locked down.

 

[ianwood]

Naza GPS protocol decoded:

http://www.rcgroups.com/forums/showthread.php?t=1995704

CAN bus messages have been partially decoded as well. Waiting for someone to decode ground station so we can use an Arduino to send waypoints to the Naza.

 

[gDallasK]

Interesting, didn't know that about the f450 top frame. What are you going to do with that? You can't replace the main board with it...

I'm not going to use a Phantom circuit board at all - I just need a flat platform to mount the Naza hardware and receiver on. Essentially it will be the same as the electronics & connections in an F450 (i.e. no circuit board)

 

[OI Photography]

Interesting, didn't know that about the f450 top frame. What are you going to do with that? You can't replace the main board with it...

I'm not going to use a Phantom circuit board at all - I just need a flat platform to mount the Naza hardware and receiver on. Essentially it will be the same as the electronics & connections in an F450 (i.e. no circuit board)

How will you feed power to the ESC's?

 

[gDallasK]

Interesting, didn't know that about the f450 top frame. What are you going to do with that? You can't replace the main board with it...

I'm not going to use a Phantom circuit board at all - I just need a flat platform to mount the Naza hardware and receiver on. Essentially it will be the same as the electronics & connections in an F450 (i.e. no circuit board)

How will you feed power to the ESC's?

Wired to the battery connector with a Naza V2 PMU for everything else.

 

[OI Photography]

How will you feed power to the ESC's?

Wired to the battery connector with a Naza V2 PMU for everything else.

Cool, so it'll basically be a 450 in a Phantom shell, except for the ESC's and motors? Keeping the Phantom LED or using the regular NAZA one?

 

[ElGuano]

The f450 does have a circuit board, but it's a PDB only on the bottom plate. You can definitely set up the phantom to run off the pmu and create a wiring harness to serve as the PDB (or install a cheap 4-pad PDB). Copper wiring and solder is quite heavy though, I'm pretty sure you will incur a weight penalty doing it this way over keeping the stock main board (even with the bec circuitry sitting unused).

 

[gDallasK]

How will you feed power to the ESC's?

Wired to the battery connector with a Naza V2 PMU for everything else.

Cool, so it'll basically be a 450 in a Phantom shell, except for the ESC's and motors? Keeping the Phantom LED or using the regular NAZA one?

Planning to use the NAZA LED.

 

[gDallasK]

The f450 does have a circuit board, but it's a PDB only on the bottom plate. You can definitely set up the phantom to run off the pmu and create a wiring harness to serve as the PDB (or install a cheap 4-pad PDB). Copper wiring and solder is quite heavy though, I'm pretty sure you will incur a weight penalty doing it this way over keeping the stock main board (even with the bec circuitry sitting unused).

Here's the F450 Upper deck fitted into the Phantom 2 lower fuselage. The mounting lugs were cut down by 2mm to give a bit more headroom. The curves fit the shape of the fuselage perfectly. All I had to do was drill four holes (accurately) to mount the deck in the Phantom.

 

[gDallasK]

The results of this evening's work. Plenty of room on the platform to squeeze in the Zenmuse controller later! The ESCs arrived today and hopefully the power breakout cable will arrive tomorrow so we can get my Phantom SP finished and get to the maiden flight!

Still need to fit the LED / USB module. Considering using epoxy resin to glue it to the flat surface above the battery compartment door (at the bottom of the picture) or attaching it to the landing leg

 

[OI Photography]

Still need to fit the LED / USB module. Considering using epoxy resin to glue it to the flat surface above the battery compartment door (at the bottom of the picture) or attaching it to the landing leg

Your needs have been anticipated and 3D printed: https://www.shapeways.com/model/1728011 ... shell.html

Btw...no PPM output on that Orange Rx?

 

[gDallasK]

Still need to fit the LED / USB module. Considering using epoxy resin to glue it to the flat surface above the battery compartment door (at the bottom of the picture) or attaching it to the landing leg

Your needs have been anticipated and 3D printed: https://www.shapeways.com/model/1728011 ... shell.html

Btw...no PPM output on that Orange Rx?

Thanks for the link. Ordered a black one.

The Orange Rx is a Spektrum version so no PPM output. Unfortunately.