Harry's GPS Suite Forum

Hi, I'm trying to decide on next GPS purchase and Vbox Sport is at the top of my list. I like 20Hz update rate and ability to log data to SD card. On the other hand I used to race with older Vbox'es and I have mixed bag of experience related mostly to GPS accuracy. My previous unit (older vbox) was loosing signal from time to time in hill climb events, even though I used external antenna. I've heard that Sport has improved GPS chipset, however Racelogic specs are limited on details. As many of you are using Vbox Sport - let me know what is your experience, especially compared to other units? I'm really interested in some technical details. What accuracy can I expect - the website states 5m (CEP), while (much cheaper) XGPS160 provides 2.5m (CEP) according to specs. Does Vbox Sport support GLONASS? How about update rate - is it stable 20Hz or may vary? Looking forward to hear some feedback

regards,
M.

I assume all named devices will deliver the same best case accuracy. I have learned a lot about the different approaches to derive accuracy and know you can not really trust in what is reported. For devices delivering HDOP, LapTimer derives a statistic value for accuracy. For internal GPSes you get an accuracy (no HDOP) and can trust them - or better not. The best approach supported is using values delivered by the NMEA GBS sentence, but none of the named devices comes with it.

For HDOP derived accuracy a general GPS shift is not taken into account at all. This leads to "shifted" recordings not matching the track driven. To work around this shift, one needs a ground based reference system (GBAS). The K-Index provided in the upcoming LapTimer version 19 will give you an indication on shifts currently occurring (atmospheric disturbances).

Back to your question: the most important question for the named GPSes is the share in time they are really delivering best case accuracy. So e.g. are they able to keep a high number of satellites locked all time? As long as you are using the antennas build into compatible GPSes, I found the Dual very good and the Sport weak. This changes as soon as you add an external antenna to the Sport (you can put onto the roof). This makes the VBOX a very reliable and better device with high accuracy across the track. One of the reasons the Sport may be weaker when not adding a boosting antenna is it is a GPS only chipset, no GLONASS support. This in turn reduces the number of satellites available.

A price / value discussion is difficult from my point of view as priorities are different. The only item I'd like to raise is "if you spend a fortune on a GPS device, check Autosport Lab's RaceCapture/Pro MK2 devices too". It is even more expensive than the VBOX but comes with 50 Hz GPS/GLONASS plus OBD, plus CAN, plus analog / digital sensor connections and has an external GPS antenna. It will be supported by HLT starting with version 19. So far they offer a BT option only (which means Android only), but maybe they will add a WiFi option for iOS later too. I have no on track experience with it so far, so I can't judge lock stability for this device.

Just my 5 cents. I have some experience and tons of user feedback, but I'm not a GPS manufacturer!

- Harry

Harry, thanks for extensive feedback and explanation. I was already looking Autosport Lab's RaceCapture/Pro MK2, but skip this option as I mostly drive rally sprints where start and finish line have different locations. Most hardware lap timers I've tested have issues to set it that way (it's not possible or require track preparation on pc) and I didn't find enough info about RaceCapture capabilities in this area. RaceCapture seems pretty impressive and price is not a deal breaker. If v19 supports it, I will reconsider

v19 is away just 3 weeks. When using LapTimer, you can certainly time one way tracks using the RCP.

Harry

I'm already beta testing v19

I think the internal antenna problem with the VBOX Sport is the lack of a good ground plane if it's mounted using a suction cup on the windshield well above the dashboard. Even the dashboard probably doesn't have enough metal and it's too close to the edge of the hood.

Harry wrote:As long as you are using the antennas build into compatible GPSes, I found the Dual very good and the Sport weak. This changes as soon as you add an external antenna to the Sport (you can put onto the roof). This makes the VBOX a very reliable and better device with high accuracy across the track. One of the reasons the Sport may be weaker when not adding a boosting antenna is it is a GPS only chipset, no GLONASS support. This in turn reduces the number of satellites available.

Harry, and if you fix the Dual XGPS160 onto the roof, will it perform better / will it make a better solution than the VBOX Sport ?
Many thanks !

I can't say. In case both devices have a perfect "view to the sky" they will have enough satellites to operate at their optimal performance. The Dual's advantage to have nearly double the sats available due to GLONASS support, will not count here any more. Losing the lock will not happen either. I doubt the devices will use a completely different level of filtering in this situation, so the Dual will still apply a (more consumer focussed) filter making the speed read outs less precise than the VBOX's less aggressive filter. So at least applying this rather theoretic ideas, the Dual will be not show the same track focussed characteristics as the VBOX in perfect conditions. To verify this, one needs to run tests - which I haven't.

- Harry

Understood, many thanks !
Should we ask Dual for a XGPS160 firmware with an option to disable filters ?
Is it what you expect on LapTimer side, samples which have not been filtered ?

Every GPS chip filters data to remove noise. It is a question of the right amount for an individual receiving condition and operation purpose. In case you have bad receiving condition, you need to filter stronger and vice versa. Further discussions on this need to be ran with device or even chipset manufacturers. I'm really not the expert on this level.

- Harry