Speed going negative when coming to a stop

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Btwyx 
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Speed going negative when coming to a stop

Post by Btwyx  »

I'm using the lap timer V18 with a GoPoint BT1 ODB dongle, when the car comes to a stop, the reported wheel speed looks like its going negative, but this is being reported as a large positive speed, like 6553.5km/h (I assume this is -0.1km/h). I hadn't noticed this prior to today because the interesting lap data doesn't usually involve coming to a stop. Today I was practicing with a new XGPS160 (at 10Hz) unit while driving on the street. Looking at old data it seems this has happened previously (using an XGPS150 at 5Hz).

When this happens it makes the speed chart for the lap useless, as the trace is all along the x axis, with a spike up to 4000mph occasionally. I think I may have noticed this once or twice previously, but not realised why there was the glitch in the data.

Here's an extract of the data, coming to a stop.

Code: Select all

351	17-May-14	22:55:04.9	246.7	37.391555	-122.072993	0	0	13.9	45.603675	331.7	1	2	14	1.01	3	2.8209	1.752826	1	0.05	-0.09	37.391544	-122.073018	840	-3			2.27	2.9	1.801976	0.03	0	0.6	88	0	27	0
351	17-May-14	22:55:05.0	246.8	37.391555	-122.072993	0	0	13.9	45.603675	331.7	1	2	14	0.79	2.3	2.821	1.752888	1	0.05	-0.09	37.391544	-122.073018	876	36			2.27	0.5	0.310686	1	0	0.6	88	0	27	0
351	17-May-14	22:55:05.1	246.9	37.391555	-122.072993	0	0	13.9	45.603675	331.7	1	2	14	0.79	2.3	2.8211	1.75295	1	0.04	-0.09	37.391546	-122.073013	884	8			2.27	6553.5	4072.156094	1	6	0.6	88	0	27	0
351	17-May-14	22:55:05.2	247	37.391555	-122.072993	0	0	13.9	45.603675	331.7	1	2	14	0.79	2.3	2.8212	1.753012	1	0.04	-0.1	37.391546	-122.073013	871	-13			2.8	1.9	1.180605	0	0	0.6	88	0	27	0
351	17-May-14	22:55:05.3	247.1	37.391555	-122.072993	0	0	13.9	45.603675	331.7	1	2	14	0.79	2.3	2.8213	1.753075	1	0.04	-0.1	37.391546	-122.073013	879	8			2.5	6553.5	4072.156094	0	6	0.6	88	0	27	0
351	17-May-14	22:55:05.4	247.2	37.391555	-122.072993	0	0	13.9	45.603675	331.7	1	2	14	0.79	2.3	2.8214	1.753137	1	0.04	-0.1	37.391546	-122.073013	883	4			2.5	6552.9	4071.783271	0	6	0.6	88	0	27	0
351	17-May-14	22:55:05.5	247.3	37.391555	-122.072993	0	0	13.9	45.603675	331.7	1	2	14	0.79	2.3	2.8215	1.753199	1	0.04	-0.1	37.391546	-122.073013	825	-58			2.5	6552.8	4071.721134	0	6	0.6	88	0	27	0
351	17-May-14	22:55:05.6	247.4	37.391555	-122.072993	0	0	13.9	45.603675	331.7	1	2	14	0.79	2.3	2.8216	1.753261	1	0.04	-0.1	37.391546	-122.073013	812	-13			2.5	6552.4	4071.472585	0	6	0.6	88	0	27	0
351	17-May-14	22:55:05.7	247.5	37.391555	-122.072993	0	0	13.9	45.603675	331.7	1	2	14	0.79	2.3	2.8217	1.753323	1	0.04	-0.1	37.391546	-122.073013	847	35			2.5	0	0	0	0	0.6	88	0	27	0
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Harry
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Re: Speed going negative when coming to a stop

Post by Harry »

OBD values are interpolated to the GPS fix times. I assume there is an overflow when going to zero (which is fortunately not a typical track scenario :-) ).
Please send a full CSV or HLPTRL export to me (Harry@gps-laptimer.de). Please add a note "negative wheel speed".

- Harry
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