uBlox LEA-6H GPS module - 5Hz or 2Hz? - Discussions

In an attempt to increase horizontal position accuracy, I have been researching inexpensive GPS modules. In my initial research, i was looking at my current module, the uBlox LEA-6H and noticed a discrepancy in the data at hand.

According to 3DR, their LEA-6H GPS/compass has an update rate of 5Hz:

http://store.3drobotics.com/products/3dr-gps-ublox-with-compass

...however.... according to uBlox, the manufacturer, the LEA-6H datasheet shows an update rate of 2Hz:

http://www.u-blox.com/images/downloads/Product_Docs/LEA-6_DataSheet_%28GPS.G6-HW-09004%29.pdf

the 6A, S and T-0 all feature a 5Hz update rate while the H and T-1 feature 2Hz

Who is lying?

Did 3DR place a large enough order to get an OEM spec?

Can anyone confirm uBlox's data sheet or 3DR's claim?

Replies

Ted Weerts May 5, 2014 at 11:44am

Wayne,

this is the response I got from 3DR when i sent them an email:

Thank you for contacting 3DR Tech Support.

The current GPS is configured to work at 4Hz, on the configuration file (http://ardupilot.com/wp-content/uploads/downloads/2013/05/3DR-Ublox...) you will see the CFG-RATE (line 65) the fifth value as FA which is 250ms (FA hexadecimal = 250 decimal).

If you want to change this value you will need to build a special cable to connect the GPS (5V, GND, Tx and Rx) to a FTDI cable (to convert to USB connection) and to the computer and run the u-center software to modify the value (http://www.u-blox.com/en/evaluation-tools-a-software/u-center/u-cen...).

Here is a related information, it's for the old GPS version but attached is the current version pinout in case you want to build the custom cable:

http://copter.ardupilot.com/wiki/common-ublox-gps/

Regards,
Roger
Tech Support
3D Robotics

TL;DR

the GPS from 3DR is default configured to 4Hz, but is can be changed.

I am no master of GPSs, but the way I read the data sheet and 3DR's response is that the LEA-6H has an update rate of 2Hz. So even is you change the update rate to 200ms, the GPS chip will only update its position every 500ms and you will simply be oversampling. ...or am I misunderstanding the way these things work?
- Wayne Holder > Ted Weerts May 5, 2014 at 10:47pm
  
  I have the original ublox module 3DR sold (the one without the compass.) It was advertised as able to update at 5Hz, but there now seems to be a new data sheet here:
  
  http://www.u-blox.com/images/downloads/Product_Docs/LEA-6_ProductSu...
  
  that contradicts this. Specifically, is says that only the ROM version of the LEA-6H can run at 5Hz. The Flash version (part number LEA-6H-0-002, which is what's on my module) is only able to run at 2 Hz. This is noted on the 2nd page of the above link, where it says:
  
  Navigation update rate up to 5 Hz (ROM version), 2 Hz (Flash)
  
  Wayne
Wayne Holder May 5, 2014 at 8:58am

I'm wondering the same thing. MY LEA-6H is configured to use a 200 ms update interval (5 Hz) but, when examining the iTOW field of the position record to see the timestamp between successive messages I see a difference of 400 ms, which is only 2.5 Hz.

Note: for reference I recently updated the firmware in my LEA-6H to version 7.03.

Wayne