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Internal vs external GPS modules and their effect on lon/lat G accuracy

Professional Motorsport Data Analysis

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Hi everyone,

I'm having a bit of an issue at the moment with the GPS lonG and latG channels on my MXm datalogger when using RaceStudio2.

Previously to installing the MXm I had an AiM EVO4 datalogger installed under my motorcycle's seat, fairly centrally situated within in the bike. It had an external GPS module that was mounted to the rear fairing behind me. The GPS lonG and latG channels from this setup were very clean when using my lean angle maths channels, as well as when analysing my GG plot. See the attached photo, the green trace is the EVO4 setup.

However, after installing my AiM MXm system the GPS lonG and latG channels are incredibly jagged/oscillating and I can't figure out how to remedy this. The MXm is mounted at the front of the car replacing the stock dash/cluster, and the GPS module is internal within the logger. See the attached photo, the red trace is the MXm setup.

Both the EVO4 and MXm were logging GPS lonG and latG at 10hz. Does the placement of the GPS module play a role in how smooth the data comes through the GPS channels? For example, is there a difference between mounting the module in the front of the bike vs the rear of the bike due to more movement at the front vs the rear which is more stable? If I go to an external GPS module and mount it to the rear of the bike like I had before, would this remedy the problem, or is there another issue at play? It makes it hard to do a comparison with a reference lap when the MXm GG plot trace pings back and forth so much.

Attached Files

GPS works via line of sight. Generally the mounting requirements of a GPS antenna are an unobstructed 360 degree view of the sky, with metal covering being a big no no.

Quite often when GPS units are mounted near the pillar on the dash of a car, you will see the number of connected satellites change when the vehicle changes direction, as the metal pillar obstructs satellite locks.

Some later GPS units also use differential GPS technology for increased positional accuracy.

I have had issues with our GNSS gps pucks being mounted too close the the window bars on the hood of our cars in the past. even just cutting off a little over 3/4 of it's line of sight with the sky is enough to cause issues. We install all of our GPS antennas on the roof of the car now and don't have many issues. keep in mind too that the sensor doesn't see everything. The usable half dome is parallel to the surface of the sensor. The sensor doesn't have to be perfectly parallel but more that say 30* off and the number of satellites it sees will start to fall off.

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