Why is the "Bad Elf" not recommended?

Discussion related to external and internal GPS sensors
toysareforboys
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Why is the "Bad Elf" not recommended?

Postby toysareforboys » Sat Mar 16, 2013 8:28 pm

Ok, I'd really like 10hz. The Bad Elf BE-GPS-1000 (hard connect, not bluetooth) looks like a really nice unit.

My reasons for wanting the Bad Elf:

10hz update rate
forward facing antenna (the iPod will be mounted on a flat metal surface facing up).

I read about some charging jack issues with the Emprum UltiMate GPS, as well as the antenna is rear facing so might not get great signal in my application.

I asked about the Bad Elf in the v17 announcement thread and Mr. Harry replied:

Harry wrote:The Bad Elf is not recommended although it delivers 10 Hz. Please check http://www.gps-laptimer.de/Compatibility.html for the details.
Of course that page doesn't really go into the details. So they don't have an API available, who cares if it can do 10hz through the apple interface?!?!? Is that the only issue??

I know Elf gives crappy support, lies, etc. And Emprum gives great support, etc. but I really want 10hz. I'm ready to buy my hardware today, need to know asap.

Thanks.

-Jamie M.
(P.S. Device is iPod Touch 4th Gen 8gb with Harry's Lap Timer Pro, soon to be v17 GrandPrix edition)


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Harry
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Re: Why is the "Bad Elf" not recommended?

Postby Harry » Sat Mar 16, 2013 8:48 pm

For any GPS not integrated directly, LapTimer receives GPS information through Apple's location service. Apple's location service is not designed to support highly accurate timing information, instead it will deliver wrong timing for individual fixes - up to seconds. In case you want more background on the recommendation, read http://www.gps-laptimer.de/GPS_and_Accuracy.html, particularly the section on "Time of position fix". 10 Hz delivered with arbitrary timing effects actually needs to be rated the same as the internal GPS (same effect) - except you get more (wrong) fixes. So from my PoV there are good 5 Hz options (Dual + Emprum), and a good 20 Hz option (VBOX Sport). I do not consider the two Apple compatible 10 Hz devices available (Garmin Glonass and Bad Elf) as good options for on track use.

- Harry


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Re: Why is the "Bad Elf" not recommended?

Postby toysareforboys » Sat Mar 16, 2013 9:07 pm

Thank you for the link Harry, it's exactly what I needed to know. I didn't know that the Apple location service messed with the data, I thought it was a raw pass through, which obviously it's not.

I'll have to come up with a solution for my motorcycle then. Possibly a 30pin extension cable so I can flip the UltiMate the right way around. I was thinking about mounting my iPod on my handlebars (I already have a steering stem mount for it), but not sure if that'll throw off the acceleration numbers (not that they are very important to me anyway) or if the vibrations would otherwise affect it.



-Jamie M.


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Re: Why is the "Bad Elf" not recommended?

Postby Harry » Sat Mar 16, 2013 9:13 pm

For motorcycles you need to calculate (instead of measure) acceleration anyway. Due to the lean angle, you will get 0 G lateral most of the time.

- Harry


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Re: Why is the "Bad Elf" not recommended?

Postby toysareforboys » Sat Mar 16, 2013 9:15 pm

Harry wrote:For motorcycles you need to calculate (instead of measure) acceleration anyway. Due to the lean angle, you will get 0 G lateral most of the time.
Ahhhh, yes yes, the lean angle :)

-Jamie M.



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