Harry's GPS Suite Forum

Harry;

The tweaks in the expert settings labeled "Accelerator Tweaks"... I assume those are for the internal iPhone accelerometer, correct? What are the optimum settings for these 2 categories: Update rate frequency and Use laptimer calibration

I wanted to run at the highest frequency to obtain the most data so I dialed it up to 100 Hz. I usually use over 2500 Hz when acquiring data via NI LabView along with PCB piezotronics accels but the high update rate in the iphone seemed to produce data that was very coarse. Would the smoothing the recalculation field help? Is 100 Hz a good setting or should I be using another rate? It looks like 10Hz is the standard but I would certainly like a little quicker data if possible. I would like to be as accurate as possible.

Can you please explain the calibration methods utilized when the radio button is on VS off? I reset the settings and it was defaulted to off but I have a 0.1g offset constantly currently in my videos. Would selecting your method alleviate that issue?

Thanks a ton for an awesome product. I have slowly worked out the "bugs" or my lack of usage knowledge and am looking forward to my PIP videos with the 160 and the BT1 this Saturday from Autobahn CC South.

-Nick

Actually I do not want users to change any expert setting - except on advice to fix an issue. So no, there is no documentation on these settings and there will be no documentation

Accelerometer standard setting is 30 Hz. Except when using the VBOX Sport (20 Hz) GPS, please do not change this values as it will not generate any benefit when raised. Acceleration values can be sampled at a high rates but need some low passing as values are pretty noisy. Acceleration should be 3 times the update rate of GPS (which dictates the storage scheme currently), so 30 is o.k. for 10 Hz GPS sensors and below. Raising the accelerator rate beyond that will simply add load to the system but not change recordings.

"Use LapTimer Calibration" is a test setting, please turn it off in case you turned it on. A constant offset on calibration means you were not standing on a flat surface when the initial calibration step took place. Next time you see calibration is off while standing still on flat surface, please either touch the acceleration circle on Video View, or any of the Max G gadgets (GPS View, Timer View...). This will restart calibration. Once you have reset calibration, it should go to zero after a few seconds.

- Harry

The 30Hz setting results in oversmoothed accelerometer data for me. It's not anywhere near as bad as the yaw rate plot, but it still lags real acceleration enough to show up when, for example, the lineal acceleration is integrated and compared to measured speed or the lateral acceleration calculated from speed and yaw rate is compared to the accelerometer data.

It's probably not significant on a track, but it really shows up at an autocross where there are frequent and rapid changes in direction.