I don't believe your GPS'd speeds!
 

Some people use a GPS to measure the speed of their R/C car. But the other day, I was driving around and my GPS "hiccuped" and showed an impossible reading of 177mph. I drive a Mazda3 S (hatch) with a computer limited top speed of 118mph (verified). And I am the only one who uses this GPS.

The only software manipulation done was to crop and resize...

http://scriptasylum.com/forumpics/gps_bad.jpg

Haha. Thats a one off. I haven't seen that before. Maybe you time warped a couple feet.

Not to mention your great runtime ! 177 mph for 45 minutes, you have some sick lipos

GPS am not work... http://www.beatyourtruck.com/forum/i...on_scratch.gif

fastest Mazda 3 on the planet!

are u sure it's miles? maybe it's meters :)
slowest mazda 3 on the planet :)

Did someone throw the GPS unit from the back seat to the front seat while you were driving at that 118mph? lol

That's pretty funny. While on an airplane, my brother turned on his gps and hit 377 mph.

I tried that excuse with a cop / judge once! :intello: (I think I was 19 years old), I was in a VW bug and he clocked me at 95, :gasp:

I was trying to tell / explain the judge that my car doesn’t go that fast down hill with a 20mph wind behind it!..:rofl: he laughed and fined me $365.00 and cost me two points :diablo:

Dam GPS units!...:wink:

Yes, it's mph. If it was using imperial units, it would be kph. :wink:

I don't know what happened either. One minute the top speed was ~115 (I just HAD to test that 118 mph top speed :smile:), and the next it was at 177. It always stays in its little holder so no I didn't toss it anywhere while going 118. Futhermore, I'd have to throw it around 50mph forwards and as I'm already in the front seat, it would be slightly bad for its health (not to mention whatever it hit). :smile:

I'm sure for the most part, GPS is accurate, but I thought this was interesting. Makes you wonder now if all measurements are totally accurate. Hmmm.

GPS speed just works on interpolation of your position at different time intervals.

If you had a false GPS read i.e. put you several 100 yards ahead the math gives you an off MPH reading.

^ Maybe it had to switch over to another satellite right then? That could account for the hiccup.(?)

That, or you were doing some automotive skydiving......

GPS works by triangulation normally of 6 or more sat's so shouldn't be an issue. But I've occasionaly had it sometimes when driving down the highway and suddenly and temporarily think I'm on the parrallel rd.

Yeah, just a random hiccup.

Having played with some data logging gps systems recently I have to say that this isn't that uncommon. The gps uses a lot of clever maths to smooth out readings but sometimes it doesn't always work. If you consistently get the same speed doing speed runs with an RC car then it is most likely accurate though.

Wow it's official, Mazda has entered the supercar arena!

I have seen this before, buddy of mine had one stuck to his sled, a Rev 600, and he got I think it was 638 mph.... ya they ain't that fast are they. The sledheads love GPS, because there is so much trackspin (especially un-studded) that the speedo is almost useless........ but they are still prone to error, sometimes significant error!

lol, even the 'speed3 doesn't go up to 177 (set to 155 IIRC).

What was your estimated max speed anyway and do the averages seem right?

Dodgy Top Speed Calculations
 

I've also watched plenty of people on you tube using their radar guns at the wrong angle, casting some doubt on their actual top speeds.

Does angle really matter as long as you are pointed in the general right direction? Radar guns use the doppler effect (phenomenon where frequency changes with speed rather than simply using speed = distance/time) to calculate speed and a wrong angle would reduce the speed if anything I would think.

Angle could be important if the radar is picking up a target other than the intended. Multipath (false targets) could also be a source of errors with radar.

That would be true for radaring in an environment with multiple moving objects, but when clocking a single R/C car amongs stationary objects, I wouldn't think those would apply.

Not really sure how much of an inaccuracy it causes, but Bushnell make a big deal out of it in the instructions.

"If the target is in a direct line (collision course) with the radar gun the measured speed will be exact. .....The measured speed will decrease as you move off this centre line. This phenomenen is called Cosine Effect, etc, etc.

As I said, not sure how much of an effect it has on Rc cars.