Looking to build a mount to capture data with TrackAddict, I won't be using video recording on the phone, just data which can be blended with GoPro footage later. From what I can find, lying the phone flat in the car with the top facing forward like the diagram below would be best for this, correct?
Get a Bluetooth GPS reciever with a higher sampling rate, it won't cost much and will be far more accurate than the internal phone GPS. I used a Garmin GLO but I think there are better ones now.
If your phone gps is the typical 1hz system, you might as well just save the effort and leave it in your pocket because the data is going to be equally worthless regardless of location or orientation.
I ran my iPhone straight up and down in portrait orientation with no external GPS at a time trial back in August. The transponder and the iPhone with Track Addict were usually within .1 second of each other on 1:48-1:50 laps (.1% error) and the largest discrepancy was .18 seconds. Good for timing a time trial event...nope. Good for playing at the track and getting a feel for whether or not you are improving...I think so.
When used for AutoX I have had considerably larger discrepancies.
Was thinking more about accelerometer & gyro/compass data and OBD2 logging than GPS, I ran some tests and it looks like this phone has a 2Hz update rate, this is just filling in for a couple events until I can get a proper racing data logger installed in the car, I can integrate external timing data into the logs so I won't have to rely on GPS for that.
GameboyRMH said:Was thinking more about accelerometer & gyro/compass data and OBD2 logging than GPS, I ran some tests and it looks like this phone has a 2Hz update rate, this is just filling in for a couple events until I can get a proper racing data logger installed in the car, I can integrate external timing data into the logs so I won't have to rely on GPS for that.
This is the way. I moved to a car with an MXL2 and there's no going back. My driving has improved dramatically.
I'm looking at a RaceCapture Track Mk3, I liked the RCP Mk1 I got for my AE92 back when they were being crowdfunded.
I use track addict just as a lap timer, which means mounting it vertically so I can see it. The predictive lap time is also great for experiments. It's within .01 seconds of the official time via transponder.
Update: Finally had time to do some data analysis last night, I ran this setup at the post-Challenge track day at the FIRM. Overall, this setup is actually an outstanding value for money and there are only a couple of severe weak spots. I ended up placing the phone like in the diagram in the first post which worked great for accelerometer readings. For overall lap times I was comparing the TrackAddict output to the track's transponder system and like Berck said it was within a hundredth. Weak spots compared to a serious-business racing data logger:
- GPS speed & heading tracking: This was hot laggy garbage and where you could really tell the system was polling GPS data at 1Hz, compared to my RCP getting GPS data at 10Hz (with options for silly storage-guzzling rates like 100Hz or even 200Hz) which is at least as good as any mechanical speedometer. In terms of lap times and position tracking though, apparently there is no clearly discernible difference between the two, likely due to prediction and averaging algorithms applied.
- Number of logging inputs: This will affect anything logging via OBD2 vs. Canbus or direct sensor wire-up, so it could affect a dedicated data logger attached in the same way as well, but with OBD2's '80s-tastic data rate the more inputs you log, the slower you can poll them, so you have to choose what you want to log carefully rather than logging everything and the kitchen sink just because it could be nice to have.
- Reliability? Not sure if the software or some hardware is at fault here, I mainly suspect an OBD2 hub device that my BT-OBD module was connected through, these are known to be troublesome. The OBD2 connection frequently dropped out for significant periods of time as you can see by the activity light and blue graph on the left of the video. Next time I log data I'll try with the BT-OBD module connected directly to the ECU and see if there's any difference.
Racebox is having a massive sale on the GPS receiver with their software or grab the actual Racebox and use that. I got mine for under $280 shipped which is pretty awesome for a track day lap timing device.
Updating this thread again, it seems the OBD2 hub was a red herring, I connected the BT-OBD2 module directly to the port and the problem was far worse, to the point that I got almost no OBD2 data logged. Next suspect is the number of BT devices the phone was connected to. Next time I'll go through the hub again but I'll disable bluetooth on my smartwatch and the car's headunit so the phone will only be connected to the OBD2 module via BT.
Edit: Also wondering if my BT-OBD2 module could use an update? It's an older ELM327 module and there are newer BLE modules out there now...
I am having a real problem with my Android phone connecting to my external GPS. No matter what I do, Track Addict defaults to the internal GPS. I wish there was an option to turn that off and force it to connect to external only!
Thought I would update this again since I linked to it, I tried testing with all other BT devices disabled so my phone would only have the OBD2-BT device to communicate with, there was no difference. The next suspect is the BT signal strength, there are some bits of metal and human between the OBD2-BT device and the phone after all. Next thing I'm going to try is putting the OBD2-BT device right next to the phone with an OBD2 extension cable.
Also I've found that the GPS only works really well with a very strong signal, if it degrades your timing can go way off, showing laps up to 2 seconds faster or slower than anything you could confirm on video, so keep a close eye on the number of locked satellites.
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