Cheap rate compass

[Javelin]

I was chatting to a guy with a very flash drone the other day.
It is fitted with a gps and gyro with 9 axis stabiliser and apparently a rate of turn sensor as well.
The whole thing including the transmitter, HD camera and posh bag was £850.

I wondered if there is another route to get a decent rate compass apart from the £500 + that simrad want for just the compass

 

[Lon nan Gruagach]

I would guess that the compass in that drone is little better than
http://www.ebay.co.uk/itm/like/152286324577?chn=ps&adgroupid=40208487538&rlsatarget=aud-295856145004%3Apla-470338998192&abcId=923846&adtype=pla&merchantid=113112059&poi=&googleloc=20342&device=c&campaignid=738085096&crdt=0

Your best bet for cheap compass and rate of turn sensor (and gps while we are at it...) would be a tablet. Wiuldnt be too hard to get it to punt out NMEA for each of its sensors.

 

[pvb]

Doing a search on here might help - here's one thread for starters http://www.ybw.com/forums/showthread.php?383299-Adding-external-Gyro-to-Type-100-Autohelm

 

[Javelin]

Yes, had a look at some old threads but most are well before the recent popularity of Drones and recent tech.

 

[GHA]

Something like this..?
https://www.sparkfun.com/products/13762

Plugged into a Raspberry Pi running openplotter will talk to it and spit the data out over wifi

https://sailoog.gitbooks.io/openplotter-documentation/content/en/imu_sensor.html

 

[maxi77]

I suspect if you want to fit a rate gyro to an auto pilot that will accept one all you really need to do is find out the interface and buy a rate gyro to match it. Since they became cheap as chips they are easy to obtain and I suspect the autopilot manufacturer uses an off the shelf component. I suspect a wifi link might have latency problems.

 

[Javelin]

Something like this..?
https://www.sparkfun.com/products/13762

Plugged into a Raspberry Pi running openplotter will talk to it and spit the data out over wifi

https://sailoog.gitbooks.io/openplotter-documentation/content/en/imu_sensor.html

Kinda proves the point with that 9 axis sensor costing just $15

Is it possible to convert the output to nmea 2000 ?

 

[GHA]

Is it possible to convert the output to nmea 2000 ?

Might be. Not being one to the rich I don't have any nmea2000 unboard to test it.
https://sailoog.gitbooks.io/openplotter-documentation/en/can-usb-stick.html



You might need some help to fiddle the software, they're helpful at openplotter though.

 

[lpdsn]

Kinda proves the point with that 9 axis sensor costing just $15

Is it possible to convert the output to nmea 2000 ?

Probably easier just to pump out 0183 ROT & HDG sentences and buy something to convert to N2K.

 

[Lon nan Gruagach]

Kinda proves the point with that 9 axis sensor costing just $15

Is it possible to convert the output to nmea 2000 ?

NMEA 2k is electrically compatible with automotive CAN bus.. Raspberry Pis have been use for CAN bus devices, so the electrical side can be done. All you need then is the protocol and you are rocking.

 

[adwuk]

Kinda proves the point with that 9 axis sensor costing just $15

Is it possible to convert the output to nmea 2000 ?

Yes - I created a device that plugs into my NMEA 2k network, gets its power etc and does all sorts of magical things with the data. I already had a rate compass, but it would be quite straightforward to do something similar with a 9 axis sensor.

 

[GHA]

Looks like it might be in openplotter already.? . 9dof to signalk to nmea 2000..
https://sailoog.gitbooks.io/openplotter-documentation/en/nmea-2k.html

 

[laika]

Looks like it might be in openplotter already.? . 9dof to signalk to nmea 2000..
https://sailoog.gitbooks.io/openplotter-documentation/en/nmea-2k.html

https://e-sailing.gitbooks.io/openplotter-documentation/content/en/can-usb-stick.html

...although a bit unisolated and dubious for me to be enthusiastic about connecting it to my shiny new n2k bus.

I leave it to an expert to comment on hardware quality of cheap gyro compass boards but I remember from looking at them last year that an issue is that there's quite a lot of work to do between getting raw sensor values and outputting a heading. Is it a good plan to do that in userspace on a raspberry pi if you want a reliable 10Hz output? Actually I have no idea...

 

[rgarside]

https://e-sailing.gitbooks.io/openplotter-documentation/content/en/can-usb-stick.html

...although a bit unisolated and dubious for me to be enthusiastic about connecting it to my shiny new n2k bus.

I leave it to an expert to comment on hardware quality of cheap gyro compass boards but I remember from looking at them last year that an issue is that there's quite a lot of work to do between getting raw sensor values and outputting a heading. Is it a good plan to do that in userspace on a raspberry pi if you want a reliable 10Hz output? Actually I have no idea...

There are quite a few sums to do to get a tilt-corrected compass out of the raw data. I think the sensor cheap-as-chips are the same ones you get in your expensive smart-phones [an probably in your drones too]. The sensor makers do publish a lot of theoretical background to doing the correction sums, and more software libraries seem to appear all the time - Its a while since I was thinking about trying to make one. There have been quite a few threads about using Canbus to connect to N2k too - I only have 0183 so haven't paid too much attention to that.

 

[maxi77]

https://e-sailing.gitbooks.io/openplotter-documentation/content/en/can-usb-stick.html

...although a bit unisolated and dubious for me to be enthusiastic about connecting it to my shiny new n2k bus.

I leave it to an expert to comment on hardware quality of cheap gyro compass boards but I remember from looking at them last year that an issue is that there's quite a lot of work to do between getting raw sensor values and outputting a heading. Is it a good plan to do that in userspace on a raspberry pi if you want a reliable 10Hz output? Actually I have no idea...

You do not use a rate gyro to get heading, it is used to sense the rate at which, in this case, heading is changing. Early indication of change and the rate it is changing is used to apply early correction. Early corrections tend to reduce the amount of correction and result in smoother course keeping.

 

[adwuk]

To make one I'd suggest starting with a Teensy 3.2 board, 2551 canbus chip and a 9 degree of freedom sensor. My rate compass only sends out heading and rate of turn, which would be quite straightforward. This set up could sense roll, pitch, heading, angular velocity and acceleration on 3 axes. Cost, about £50-60 plus some coding.

Edit: you will also needs to add a voltage regulator to step 12v down to the 3.3v the Teensy needs.

 

[Javelin]

And I guess I'll need to find someone to make it for say £100 ?

So £150 and I coud have something that currently costs a minimum of £550.
Sounds Like a good opportunity for a little business for someone with the nowse.

 

[GHA]

To make one I'd suggest starting with a Teensy 3.2 board, 2551 canbus chip and a 9 degree of freedom sensor. My rate compass only sends out heading and rate of turn, which would be quite straightforward. This set up could sense roll, pitch, heading, angular velocity and acceleration on 3 axes. Cost, about £50-60 plus some coding.

Edit: you will also needs to add a voltage regulator to step 12v down to the 3.3v the Teensy needs.

Probably more expensive than something like an arduino nano and 9dof board but you can get a combined microprocessor and 9dof programmable using the arduino ide, libraries available.

https://www.sparkfun.com/products/14001

 

[adwuk]

Problem with the Arduino (at least the mini) is that it doesn't have a CANBUS interface. You would have to go for a larger one, and in any case the Teensy is faster to can handle the data rates needed for a rate compass. Javelin, when do you need it?

 

[oldvarnish]

One question - why does anyone need to know rate of turn? Have I been missing something?