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Accurate Speedometers
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chrismadrid
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PostPosted: Fri Apr 04, 2008 4:39 pm    Post subject: Accurate Speedometers Reply with quote

I confess to being rather surprised that nobody really seems to be offering this (except real top end suppliers).

Normally speedos read optimistic to ensure that you're travelling legally. The spec's are out there but 5% is pretty much par for the course. GPS of course could give a 100% accurate speed - except it suffers in tunnels are very built up areas and narrow valleys.

Seems to me that it should be pretty simple to build an near error free system using GPS as well as OEM wheel/gearbox sensors plus maybe some form of gyro stabiliser for DR. If done properly the GPS could also continually recalibrate the OEM sensors in opensky condition so that in tunnels etc the OEM sensors feed precise pulse rates to car/bike original speedos.

Anybody know of any ready to go solutions? - I really do not care about navigation and hate digital readouts. Seen one or two papers but is there any kit out there?

Racelogic have a 5hz GPS only solution. but 300QUID PLUS VAT - Trimble have teh placer but it's a bit old tech.
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Skippy
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PostPosted: Fri Apr 04, 2008 9:26 pm    Post subject: Re: Accurate Speedometers Reply with quote

chrismadrid wrote:
I confess to being rather surprised that nobody really seems to be offering this (except real top end suppliers).


Welcome

I guess the car manufacturers aren't really that bothered about the accuracy. You have a number of factors like after market wheels and different tyres to deal with so they just make the speedo overread and that's good enough for them. I guess they aren't to worried if their cars appear to be going a bit faster than they really are either! Wink

Quote:
Seems to me that it should be pretty simple to build an near error free system using GPS as well as OEM wheel/gearbox sensors plus maybe some form of gyro stabiliser for DR. If done properly the GPS could also continually recalibrate the OEM sensors in opensky condition so that in tunnels etc the OEM sensors feed precise pulse rates to car/bike original speedos.


I get the impression that this is exactly how the expensive built-in sat nav systems work, and we all know how much they cost!

Quote:
Anybody know of any ready to go solutions? - I really do not care about navigation and hate digital readouts. Seen one or two papers but is there any kit out there?


If you have a Pocket PC or a PDA phone with a built-in or bluetooth GPS receiver then there are programs you can get to display the speed (and other things) on the screen.

I've not used it but GPS Skinner looks pretty cool and it might do what you want!

http://www.gpsskinner.com/screenshots.htm

If you want speed camera alerts but you don't use SatNav, then have a look at GPS Speed Sentry http://www.tchartdev.com/

You would still have to solve the dead reckoning problem for when the GPS can't get a signal, but that's a bit of a tricky one. There are solid state gyros from the likes of Analogue Devices but I don't know exactly how easy it would be to build a dead reckoning system - you'd probably have to write some software to implement a Kalman filter to mix the GPS and dead reckoning data. Confused

Good luck!
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chrismadrid
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PostPosted: Sat Apr 05, 2008 7:05 am    Post subject: Re: Accurate Speedometers Reply with quote

Skippy wrote:
I guess the car manufacturers aren't really that bothered about the accuracy. You have a number of factors like after market wheels and different tyres to deal with so they just make the speedo overread and that's good enough for them. I guess they aren't to worried if their cars appear to be going a bit faster than they really are either! Wink
Actually the reason is 100% legal

Quote:
European Union member states must also grant type approval to vehicles meeting similar EU standards. The ones covering speedometers [5] [6][7] are similar to the UNECE regulation in that they specify that:

* The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
* The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h.

The UK is a bit different
Quote:
The amended Road Vehicles (Construction and Use) Regulations 1986 permits the use of speedometers that meet either the requirements of EC Council Directive 75/443 (as amended by Directive 97/39) or UNECE Regulation 39. [12]

The Motor Vehicles (Approval) Regulations 2001[13] permits single vehicles to be approved. As with the UNECE regulation and the EC Directives, the speedometer must never show an indicated speed less than the actual speed. However it differs slightly from them in specifying that for all actual speeds between 25 mph and 70 mph (or the vehicles' maximum speed if it is lower that this), the indicated speed must not exceed 110% of the actual speed, plus 6.25 mph

In theory if your speedo does not meet this - your vehicle is NOT road approved!

Tyre wear is the reason supposedly.

Seems that in the TRUCK world this is becoming more important as the mileage is on Tachos so you want your 100% miles driven not the real 90% reported as 100%. But they all seem to link to NAV systems. Which is fair given the application (ASSET TRACKING)

Either/or GPS/DR would be a piece of cake - it's called a switch. Just found U-Blox test in New York seems they have a module. Re-calibrating manually a speedo sensor pulse is easy with Speedohealer. But so far the only GPS pulse output to drive EXISTING speedos seems to be in the racing world. GPSTrans from Race-Logic for example. They do others VERY HIGH END that would do the job - But a GRAND plus seems a bit OTT. The cost is more due to low volume than high tech imo.

Oh well - Seems a GPSTrans and a switch will be the short term solution - though I will write to U-blox.
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M8TJT
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PostPosted: Sat Apr 05, 2008 9:38 am    Post subject: Reply with quote

The thing that's puzzeling me is WHY? Confused
Or is it just because it should be possible to do it? Very Happy
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mikealder
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PostPosted: Sat Apr 05, 2008 10:08 am    Post subject: Reply with quote

If the vehicle uses an electronic Speedo then it is quite easy to do. An inductive probe on either a wheel or rear axle diff crown wheel will produce so many pulses per second, the frequency is directly proportional to speed, it is however inaccurate due to tyre wear, cornering radius differences and tyre pressure.

Next you get the GPS speed signal which is in knot’s, convert this to MPH/ KPH as required, with some PDA based hardware (CF daq) get the daq card to output a variable frequency pulse train to the Speedo using the GPS speed and (at times wheel speed), it is a lot of messing about and a CF daq card will set you back a few hundred pounds - Mike
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Skippy
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PostPosted: Sat Apr 05, 2008 11:09 am    Post subject: Reply with quote

mikealder wrote:
output a variable frequency pulse train to the Speedo using the GPS speed


Thumbs Up That would work!

The other problem to consider is that an analog speedo might not measure speed correctly throughout the range. So at 30 MPH it might be accurate but at 70 MPH it might be 3% high or low. You could overcome this by calibrating it all through the range.

The other alternative is to buy an ex-Police car with a calibrated speedo installed. ;)
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Darren
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PostPosted: Sat Apr 05, 2008 11:23 am    Post subject: Reply with quote

Skippy wrote:
The other alternative is to buy an ex-Police car with a calibrated speedo installed. ;)

Which needs to be re-calibrated at regular intervals and is 'supposed' to be measured/checked weekly Wink

as to the OP's original question, I'd have to ask why is this increased accuracy necessary? Would it bring any real benefits?
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PostPosted: Sat Apr 05, 2008 3:11 pm    Post subject: Reply with quote

There is a device called a "Speedo Healer" that can be calibrated to overcome electronic speedo's that are typically 5% to 10% inaccurate.

It's advertised as being for bikes but has been successfully installed on a 2006/7 Honda Civic and was given a 9% dropoff to compensate.

It mildly winds me up when I'm keeping pace with a Citroen C4 and his speedo is reading almost what my Talex is displaying whilst my speedo is reading about 5mph more !
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chrismadrid
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PostPosted: Sat Apr 05, 2008 4:35 pm    Post subject: Reply with quote

Darren wrote:
as to the OP's original question, I'd have to ask why is this increased accuracy necessary? Would it bring any real benefits?
Imagine you're a Financial controller in a company that reimburses mileage done in private vehicles - If all the cars read 5% OTT - suddenly you'll be paying out less. And ime paying out 5% less is alot of cash.

I can think of LOADS of advantages. No more continuous calibration of Police Speedos. Never having to worry whether you speedo is correct. All big pluses.

It's been said - but there are alot of vehicles out there with VERY optimistic speedos/odometers. And the less said about the dependency of hall effect sensors reading gearboxes etc the better - some are VERY eratic.

Most analogue electro driven speedos are stepping motors - VERY ACCURATE. There area some old VOLTAGE indicating devices about - but these will be OLD and wouldn't work off pulse technology anyway.

Is it worth the effort - That's a hard one. But avoiding a fine (and points) from a roving speed camera car would pay for it. Here in Spain alot of spped knabing is done using helicopters - they use GPS.

Found several solutions that will feed NAV systems - but only one or two destined for racing that do the odometer pulse output.

TALEX or GlobalTob HG100 etc is an alternative - cheaper too - but no use in tunnels, urban canyons or real canyons.

Still not sure but I may invest in a raceLogic GPSTrans http://www.racelogic.co.uk/_downloads/general/GPSTRAN_Data.pdf - 300quid plus VAT. Fully configurable and also has a 100kph test button. Yes it's OTT. That or see if the UBLOX AEK4R will suit http://www.u-blox.com/products/aek_4r.html - €495plus VAT. Sounds a lot but I'm almost hooked now.
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Darren
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PostPosted: Sat Apr 05, 2008 4:44 pm    Post subject: Reply with quote

chrismadrid wrote:
Imagine you're a Financial controller in a company that reimburses mileage done in private vehicles - If all the cars read 5% OTT - suddenly you'll be paying out less. And ime paying out 5% less is alot of cash.

IME very few companies pay out on odometer mileages. They use routing software to calculate the milage they will pay out.
Quote:
TALEX or GlobalTob HG100 etc is an alternative - cheaper too - but no use in tunnels, urban canyons or real canyons.

Still not sure but I may invest in a raceLogic GPSTrans http://www.racelogic.co.uk/_downloads/general/GPSTRAN_Data.pdf - 300quid plus VAT. Fully configurable and also has a 100kph test button. Yes it's OTT. That or see if the UBLOX AEK4R will suit http://www.u-blox.com/products/aek_4r.html - €495plus VAT. Sounds a lot but I'm almost hooked now.

Any modern GPS will work fine in urban canyon environments. None will continue to function in tunnels for obvious reasons. For that you need a secondary data input such as gyroscope, Tomtom's 920 and 930 have such a feature. I reviewed the Globaltop GPS Hud a while back, seehere.

If you want a speed reading that is more accurate than a factory fit speedo then ANY current GPS will offer that, of the solutions you reference, the Racelogic solution offers no more apart from a 5hz update whereas the Ublox solution does add gyroscopic data, both are way OTT for simple speed measurement?
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PostPosted: Sat Apr 05, 2008 8:40 pm    Post subject: Reply with quote

Darren wrote:
IME very few companies pay out on odometer mileages. They use routing software to calculate the milage they will pay out.
I'm paid by the mile. Several years ago, a company I billed said they wouldn't pay "that much" for a delivery to Edinburgh, and sent me a printout from their routing software which showed the mileage was only about 360 miles which they were prepared to pay for. Unfortunately for them, the printout also included the time calculation, which worked out to an average speed of close to 80mph for the entire journey (without stopping). I suggested that the Small Claims Court might find difficulty in supporting their case. They paid up!! In those days, my invoices always quoted start and stop speedo readings. I still calculate my performance using distance measured by my speedo (e.g. cost per mile = x pence, profit per mile = y pence). I am always prepared to argue these points - I travel by the route chosen by my Satnav, not by their routing software which I don't use in my van - do they want to specify the route, taking all the risks which I take (traffic, weather etc) AND the delay in departure whilst they look it up, then convey it precisely to me? I now know the firms who play this game, so before I set off, I ask them what route they'll pay for.
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chrismadrid
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PostPosted: Sun Apr 06, 2008 8:47 am    Post subject: Reply with quote

Darren wrote:
Any modern GPS will work fine in urban canyon environments. None will continue to function in tunnels for obvious reasons. For that you need a secondary data input such as gyroscope, Tomtom's 920 and 930 have such a feature. I reviewed the Globaltop GPS Hud a while back, seehere.
And this is my issue. A HUGE portion of Madrids inner ring road is TUNNEL. And what's more with 17 speed traps. Admittedly I am not that often in Madrid city anymore but...... I can also from first hand experience (TOMTOM) state that in highrise inner cities with narrow streets like Madrid - The navigation is occasionally dubious amd this coincides with a drop in satellites visible. Also the village where I work is in a real canyon. GPS systems all take far too long to acquire. This includes pro-spec ones as used by police etc.

I DO NOT WANT A SATNAV type display either. I find them distracting. This is for a BIKE too btw. So large displays are out.

Will see if we can get a GTOP cheap in HongKong when my mate goes in a weeks time - but more and more I think I'm going for a GPSTRANS to drive the OEM speedo and add a small DR digital thing like the motogadget offering for the tunnels or a switch to the OEM sensor.
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PostPosted: Sun Apr 06, 2008 8:58 am    Post subject: Reply with quote

What does the GlobalTop offer? Aside from the HUD it's a bog standard GPS so no better at coping with the conditions you describe?
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PostPosted: Sun Apr 06, 2008 10:55 am    Post subject: Reply with quote

chrismadrid wrote:
Imagine you're a Financial controller in a company that reimburses mileage done in private vehicles - If all the cars read 5% OTT - suddenly you'll be paying out less. And ime paying out 5% less is alot of cash.


I think you will find that although speedometers are designed to read high, odometers are designed to report the distance fairly accurately.
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chrismadrid
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PostPosted: Tue Apr 08, 2008 5:18 am    Post subject: Reply with quote

Darren wrote:
What does the GlobalTop offer? Aside from the HUD it's a bog standard GPS so no better at coping with the conditions you describe?
True - has more to do with test of concept (dual speedos) and GPS speedos than final result. Also it's 5Hz as is the GPSTrans - not sure if this is fast enough - though I believe it is!. It's nice and compact too! - I've tried using a SATNAV and the display is confusing. Shame there isn't a version of this for a Palm or I'd give it a go. If I had a Windows mobile device I'd have tried.

At European prices I wouldn't bother. But ex-factory Asia prices is another matter.
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