Accelerometer Calibration For Autocross

Request and discussion on new / to change features
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Composites_guy
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Accelerometer Calibration For Autocross

Post by Composites_guy » Wed Apr 03, 2019 1:58 pm

[MOVED TO FEATURE REQUESTS]

I'm using LapTimer in a formula car (not road legal) for autocross racing. It is not practical to use one of the standard preset orientations for my Android phone with this car, so I must use the individual calibration feature within LapTimer. I've read the documentation on the 4 step calibration process and been experimenting with the calibration procedure in my sedan street car on rural public roads. I've had success on the 3rd and 4th steps by driving in a straight line at 40mph on flat road for perhaps 10 seconds (until the 3rd check mark appears) and then braking very hard. This resulted in excellent acceleration calibration. Here's my issue.

A. Its not practical to calibrate my formula car for autocross with a straight-away this large. I cannot drive the car on public roads, and there's no straight-away large enough for calibration at a typical autocross event. (Harry, did you ever publish the exact thresholds for successful calibration in LapTimer which would tell us the minimum straight away length necessary?)

B. If I finally achieve a successful calibration in the formula car (for instance by purchasing track time at a large track) this calibration will be precious to me. I understand that I can "lock calibration" within LapTimer. However, it would be nice to store this calibration to a file which can be recalled if the calibration is deleted by accident. An alternative would be to add a confirmation screen that asks "are you sure that you want to recalibrate?" when you tap unlock button. Right now, all it takes is one accidental tap of "unlock" to start a recalibration which cannot be cancelled.

It would be nice if there was a way to calibrate acceleration statically (in the pits). I want to mount the phone to a vertical firewall, with the top of the phone pointing straight up, and the back of the phone pointing straight forward on the car. It seems that this could be accomplished through a 2 step process. 1. Mount the phone as desired and push a button. 2. Rotate the phone through a specified 90 degree angle and push a button. That might be complicated for some users, and it would reduce accuracy if the angles aren't measured carefully, but at least it would make calibration possible for those of us without easy access to a lengthy straight-away.
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Harry
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Re: Accelerometer Calibration For Autocross

Post by Harry » Wed Apr 03, 2019 3:52 pm

I will add "confirmation on Unlock" to my list. Supporting export and import or another method is quite some effort and will require a bigger number of users requiring this. Please understand I need to prioritize my limited time available to items relevant for many. Thanks.

- Harry
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Composites_guy
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Re: Accelerometer Calibration For Autocross

Post by Composites_guy » Wed Apr 03, 2019 3:58 pm

I understand, and thanks for replying. Is there some way I can improve my odds of successful calibration to feasibly calibrate at an autocross event? I can't find anywhere the actual thresholds that must be met to achieve calibration.
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Harry
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Re: Accelerometer Calibration For Autocross

Post by Harry » Wed Apr 03, 2019 4:08 pm

The requirements for the last calibration step are:

1) driving a straight
2) longitudinal acceleration >0.25G or <-0.25G, usually the later (braking)

"Driving straight" is detected if the four last GPS measurements were within a +-1.3 degree driving direction corridor.

- Harry
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