Using a GPS for WOF purposes - Speedometer?

[Waihou Thumper]

I have an issue with my speedometer. It works but the display is very dim and sometimes disappears all together. It could be a short and I have pulled everything apart to try and find the issue but to no avail.
I was wondering if my GPS, hard wired and attached to the bike can be used to pass my WOF?

The document obtained from LTSA is a little vague but mentions nothing and only really seems to be concerned with forward speed that has to measured and safety with being obscurred or dangerous etc...

Can anyone enlighten me? Has anybody out there tried this with a testing station or got a WOF with a GPS attached.

I still want to ride the bike until I get it remedied, in the meantime I thought I could use the GPS to pass the WOF.

I have attached the relevent document below for anyone interested in looking. Thanks everyone

[CookMySock]

Well there are two parts to that ;

1.) You can use anything for a speedo. A bicycle speedo is legal IIRC.

2.) You really have no intention of hard-wiring the GPS in place and leaving there as a speedo do you? ;) If you get stopped by the fuzz you will have some explaining to do, and your story had better be well rehearsed.

Steve

[davereid]

Well there are two parts to that ;

1.) You can use anything for a speedo. A bicycle speedo is legal IIRC.

2.) You really have no intention of hard-wiring the GPS in place and leaving there as a speedo do you? ;) If you get stopped by the fuzz you will have some explaining to do, and your story had better be well rehearsed.

Steve

DB is dead right. I have had to use a bicycle speedo ($29.95) on my CZ, as the original speedo is toast, and un-obtainium.

Bike speedos are calibrated by wheel cicumference, so you can get then perfectly accurate on virtually any wheel.

My speedo claims a top speed of 299 km/hr.. so far the CZ has managed 92, so I must try harder.

For a WOF the speedo must be lit at night.

[Waihou Thumper]

Well there are two parts to that ;

1.) You can use anything for a speedo. A bicycle speedo is legal IIRC.

2.) You really have no intention of hard-wiring the GPS in place and leaving there as a speedo do you? ;) If you get stopped by the fuzz you will have some explaining to do, and your story had better be well rehearsed.

Steve

Thanks.
If I get pulled over it wouldn't be for a speedo isssue. The cop would never know it if worked or not, because I am stopped.
It is hard wired and it would be removed etc when left unattended.
I have actully just spoken to the Testingstation and it seems that it has to be a speedo that can register up to 50kph, good working order.
If it is a GPS that can measure speed as it does, the guy seemed to think that it isn't an issue.
If he can see the speed when riding it, then I might be okay. I will in fact have two working speedometers, one of which is a bit hard to see the LED displays.....
Thanks Steve, I will give it a go I think..

[Waihou Thumper]

DB is dead right. I have had to use a bicycle speedo ($29.95) on my CZ, as the original speedo is toast, and un-obtainium.

Bike speedos are calibrated by wheel cicumference, so you can get then perfectly accurate on virtually any wheel.

My speedo claims a top speed of 299 km/hr.. so far the CZ has managed 92, so I must try harder.

For a WOF the speedo must be lit at night.

The GPS does all of that and it is more accurate than the magnet on the circumference of the wheel...It measures the speed and average, maximum and displays current just like the cheap or expensice speedos for bicycles...
It displays at night, back light on permanently, I really cannot see it being an issue here, but could be wrong?

[mujambee]

Beware that it won't work on tunnels, and may be faulty under heavy forest cover. It will also need some time to fix on satellite after power on.

We've discussed the use of GPS as speedos in a production bike, and they rejected it because of that.

[UberRhys]

I was wondering if my GPS, hard wired and attached to the bike can be used to pass my WOF?

I'm sure it can, why not. :done:


Can anyone enlighten me? Has anybody out there tried this with a testing station or got a WOF with a GPS attached.


One of my scoots has a bike speedo (magnet on the rim set up) and it flys through everytime. Even at the VTNZ nazi warehouse... :rockon:

[Patch]

Beware that it won't work on tunnels, and may be faulty under heavy forest cover. It will also need some time to fix on satellite after power on.

We've discussed the use of GPS as speedos in a production bike, and they rejected it because of that.
and some fookn hitler nazi will see it ain't standard and probably make you get it certified - just get the original one fixed

[vifferman]

My speedo's currently not working (either the sender is 'ted, or the electronic speedo corrector, or there's a loose/broken wire).
I had all the fairings off on Sunday to check it out, and fit new heated grips, but the friggin' thing passed all the tests according to the workshop manual! Then, as soon as I got it out on the raod again, it gave one or two desolutory flicks of the needle, and stopped working altogether.
Gaah! Now I have to take the fairings off again.

It's OK on the open road, as I know that 100km/h is ~5k rpm in 6th gear. However, around town, given I could be any gear, it's a mater of guesstimating, based on experience, other traffic, etc.
I've toyed with using the TomTom (I've used it on the bike before) but it's not weatherproof.

[Waihou Thumper]

Beware that it won't work on tunnels, and may be faulty under heavy forest cover. It will also need some time to fix on satellite after power on.

We've discussed the use of GPS as speedos in a production bike, and they rejected it because of that.

Is on all the time, it is always fixed to the satellites as a result. The draw of power is as much as your little clock fixed inside the speedo. I would only take it off if resting overnight etc and away from the bike out of view...
I only really want it for the WOF, once I get it I will then look into the original issue. Just cannot afford the labour and testing of the harness or similar.
Being a hand held it really works well under cover of trees, dense bush. Tunnels, yes, that could be an issue but you are only in them for a seond or two unless travelling Mont Blanc or similar...lol

[vifferman]

Crap! Damn-n-Blarst, and all that. :mad:
I am hoping my speedo corrector's fukt, rather than the speedo sender unit. Just rang for a price, and this little gizmo is over $377!!
Of course, it's also, not in stock, so is an indent item, so it'll be "money up front, 3 weeks ex-Japan."
Now here's the ridiculous bit: $377 is ~US$210 (at current conversion rates).
I checked yesterday, and I can get one from several different dealers in The Yooonarted Stites of Mrka for US$72.
Presumably, their Genuine Honda Parts are made in the Philipines, or Kazahkstan or summat, to be only one-third the price.

[BM-GS]

GPS speed should be accurate as it *usually* works off Doppler from the satellite signals, so no funnies with going round curves, up/down hills, etc.

However, bear in mind that the update is only once a second, and that in town, under trees and in tunnels reception may be a bit iffy.

Dim LCD usually attributable to a circuit-level problem in/near the display itself. New display will be $$$$, poking around behind it to see where the dodgy connection is will be major inconvenience. Your choice...

[MarkH]

works off Doppler from the satellite signals

Ummm . . . WHAT???? :no:

Unless I have somehow completely misunderstood how GPS works then I am pretty sure it does not use Doppler in any way.

[Hoon]

As has already mentioned a GPS is unreliable. It is only as accurate as its signal strength and this is affected by rain, cloud cover, tunnels, canyons, high rise buildings and also the inside of a building such as the testing station.

[Hoon]

Ummm . . . WHAT???? :no:

Unless I have somehow completely misunderstood how GPS works then I am pretty sure it does not use Doppler in any way.

Some do but only for correction. Basic position is calculated by the usual distance triangulation thing but is adjusted for the movement of the satellites and rotation of the earth.

To get the best accuracy these days they take everything possible into account including time dilation due to the satellites high speed and time slowing down (einsteins theory of relativity).

[CookMySock]

As has been observed, the GPS speed can be quite laggy, and if you are prone to sudden speed bursts before corners etc, the gps "speedo" will be quite useless at those times.

Steve

[sinned]

As has been observed, the GPS speed can be quite laggy, and if you are prone to sudden speed bursts before corners etc, the gps "speedo" will be quite useless at those times.

Steve

Sometimes very laggy - you could get up to license losing speeds and back down again and it may still read 100. Good luck if you can get a wof with a gps as the speedo but don't rely on it too much.

[Jantar]

GPS speed should be accurate as it *usually* works off Doppler from the satellite signals, so no funnies with going round curves, up/down hills, etc....


Ummm . . . WHAT???? :no:

Unless I have somehow completely misunderstood how GPS works then I am pretty sure it does not use Doppler in any way.


As has already mentioned a GPS is unreliable. It is only as accurate as its signal strength and this is affected by rain, cloud cover, tunnels, canyons, high rise buildings and also the inside of a building such as the testing station.


Some do but only for correction. Basic position is calculated by the usual distance triangulation thing but is adjusted for the movement of the satellites and rotation of the earth.....

Ok, I've had quite a bit to do with GPS algorithims for navigation (aviation related) and for speed measurement.

Doppler is not used in any manner. It is triangulation for location, and time between locations for speed. Modern units are generally high sensitivity and are not as prone to signal loss due to forest cover, rain etc. GPS will not work in tunnels and depending on the location of satelites may lose accuracy when close to high rise buildings, canyon walls etc.

One of the things to remember when considering GPS accuracy is that if the error is 10m on a particular reading it will be the same 10m on the next and the next reading. ie 10m error to the west will stay 10m error to the west while on that particular set of satelites. Another satelite coming into view will generally increase the accuracy, while losing one will decrease the accuracy. Thus an accuracy indication of +/- 10 m doesn't mean that it may be +10 m on one reading and -10 m on the next.

Speed reading on GPS are extremely accurate, with the proviso that they are averaged over whatever refresh setting the unit is set for (usually 1 second), and there is often a slight delay in indiaction when speeds are changing rapidly.

[Jantar]

Sometimes very laggy - you could get up to license losing speeds and back down again and it may still read 100. Good luck if you can get a wof with a gps as the speedo but don't rely on it too much.

Many of the old mechanical speedos with a spinning disc dampened by a magnet, are also very laggy. Its just that we didn't notice the lag.

[mujambee]

Speed reading on GPS are extremely accurate, with the proviso that they are averaged over whatever refresh setting the unit is set for (usually 1 second), and there is often a slight delay in indiaction when speeds are changing rapidly.

GPS can be fairy accurate and get very fast refresh.

Commercialy available GPS units, on the other hand....

[sinned]

I am waiting to see when the Zumo 660 is available in NZ. It sounds like the ultimate GPS toy for the bike.

[BMWST?]

bike speedo for the win....even really cheap ones will have average speeds etc.And they can be calibrtated to be very accurate

[BM-GS]

Different GPS chipsets will use the same information to calculate the position, and knowing all the stuff they do about the last fix and the current one, they can work out what they need to however they like. The weightings applied to the results of the different calculations will vary. Doppler is known as it has to be calculated to receive the signals accurately. Once the fix is established (the constellation positions are known, etc) Doppler on the received signals can be used to calculate velocity, or as a sanity check on the distance/time calc.

This was mentioned by an engineer working for a chipset vendor, I think not just with the intention of confusing the opposition by waiting for the info to go to them via me... Admittedly, some chipsets work better than others (by which I mean different chipsets have different strengths - absolute accuracy vs power consumption vs multipath resistance vs price, etc).

It's still a minor miracle to me that the damned system works at all in consumer-bought units, the way people use it & it's expected to operate.


Edit: Bugger. Let my posts in here serve as a warning never to let your fingers work without supervision.
Doppler would never work for user velocity, just as sanity for the position fix. How could a user's 50km/h or 60km/h do much to the speed of light and the speed of the satellites and the speed of the earth's rotation? This post is mostly OK, but it's in support of the premise that Doppler is used by GPS chipsets to calculate velocity, which is complete crap. And I said it. Publicly. ... Can I find a nice stone to crawl under? Hope the Edit feature keeps this post buried, where it belongs.

[mujambee]

A silly question that just came to mind: If the bike is stationary inside the WoF shop, how can they test that your GPS unit is accurate? No amount of roller speed will make that thing believe it has moved a bare mm.

[Waihou Thumper]

A silly question that just came to mind: If the bike is stationary inside the WoF shop, how can they test that your GPS unit is accurate? No amount of roller speed will make that thing believe it has moved a bare mm.

I will take it to my motorcycle shop, they test the speedo and brakes by riding the bike, simple way and the reliable way too

[Crisis management]

A silly question that just came to mind: If the bike is stationary inside the WoF shop, how can they test that your GPS unit is accurate? No amount of roller speed will make that thing believe it has moved a bare mm.

Since when do they get on the bike? All my wofs consists of a mechanical check and a chat about where the best places to ride are.....and thats at VTNZ station.

[Waihou Thumper]

Since when do they get on the bike? All my wofs consists of a mechanical check and a chat about where the best places to ride are.....and thats at VTNZ station.

My local here is good, he is quite relaxed, knows the bike and the predicament too...
I even called the VTNZ station in Hamilton and he said the idea and the reasoning is fine, couldn't see an issue with GPS.
All the issues with lag, cloud cover, bushes, tunnels etc....
I don't see this as a problem. I only want to pass a warrant, what goes on after that is immaterial really. It is the same as putting on a mates tyre to get a warrant or the spare and then changing it back to the bald one....Although you would be a bit of a plonker to do that on a bike...lol
The accuracy on my GPS is as good as +/- 2m, so that is good for the little unit. The lag, updating speed etc isn't an issue really, as someone suggested prior, the lag on a wheel is probably worse or similar. By the time the speedo registers the speed, travels up the wire to the unit, you have either changed speed, sped up or slowed for a corner.
Bike computer is fine, would consider that or take the one of my Husaberg if the WOF became an issue...

I will get it fixed, just will be a winter project and will need some patience tracing the loom, the points and where my voltage is leaking or shorting?
Bet it is sourced in a jiffy with the right tools. The work is the removal of the dash, the fairing, tank to expose the wiring harness and auxillaries.

[Hoon]

One of the things to remember when considering GPS accuracy is that if the error is 10m on a particular reading it will be the same 10m on the next and the next reading. .

No thats not true. You can't assume that an error will be identical between samples. The error range maybe the same but the value and direction will be different every time (though probably not by much in most cases but still different). Errors are due to a combination of factors from atmospheric to bouncing off buildings, not just satellite positioning.


Edit: Bugger. Let my posts in here serve as a warning never to let your fingers work without supervision.
Doppler would never work for user velocity, just as sanity for the position fix.
..... This post is mostly OK, but it's in support of the premise that Doppler is used by GPS chipsets to calculate velocity, which is complete crap.


I'm no GPS expert but Google disagrees (http://www.google.com/search?hl=en&rls=com.microsoft%3A*&q=GPS+doppler&btnG=Search) with you...especially this guy (http://www.aprs.net/vm/gps_cs.htm).



How could a user's 50km/h or 60km/h do much to the speed of light and the speed of the satellites and the speed of the earth's rotation?
Timings errors account for +- 2m apparently (http://www.kowoma.de/en/gps/errors.htm). I guess when its all about making a GPS as accurate as possible every last bit counts.

[mujambee]

I will take it to my motorcycle shop, they test the speedo and brakes by riding the bike, simple way and the reliable way too

My fault. Here they put the bike on rollers to do all those checks. Just assumed it must be the same over there. :Oops:

How can they tell if your speedo is accurate?

[Conquiztador]

Some do but only for correction. Basic position is calculated by the usual distance triangulation thing but is adjusted for the movement of the satellites and rotation of the earth.

To get the best accuracy these days they take everything possible into account including time dilation due to the satellites high speed and time slowing down (einsteins theory of relativity).

Bloody Einstein. He was soo wrong. I remember how the summers used to last forever when I was young. Now they just whizz by and its frikkin winter again! My hair is falling out faster each day and I am getting old at the speed of lightning!

[mctshirt]

As has already mentioned a GPS is unreliable. It is only as accurate as its signal strength and this is affected by rain, cloud cover, tunnels, canyons, high rise buildings and also the inside of a building such as the testing station.

I beg to differ - most (if not all) are now fitted with the Sirfstar III chip that dramatically improves the usability of GPS's. Cloud, walls, indoors, tree cover, etc interference is pretty much a thing of the past (although they still aren't magic). The best bit is a new GPS with the Sirfstar chip is not more expensive. Using the basic Garmin Etrex as an example Garmin simply fitted the Sirfstar chip, renamed the model to Etrex H and left it at the same price. In the past I would have agreed with you Hoon but the hardware has caught up enough to the theory. In my mind a GPS is a serious alternative to the traditional mechanical device which arguably suffers more inaccuracy than a GPS now.

http://en.wikipedia.org/wiki/SiRFstar_III

[Waihou Thumper]

My fault. Here they put the bike on rollers to do all those checks. Just assumed it must be the same over there. :Oops:

How can they tell if your speedo is accurate?

Just has to work, register up to 50kph, etc...according to the blurb I posted on the first post.

[Waihou Thumper]

Cloud, walls, indoors, tree cover, etc interference is pretty much a thing of the past (although they still aren't magic). The best bit is a new GPS with the Sirfstar chip is not more expensive. Using the basic Garmin Etrex as an example Garmin simply fitted the Sirfstar chip, renamed the model to Etrex H and left it at the same price. In the past I would have agreed with you Hoon but the hardware has caught up enough to the theory. In my mind a GPS is a serious alternative to the traditional mechanical device which arguably suffers more inaccuracy than a GPS now.



I totally agree. I have a Garmin and have accuracy down to +/- 2M most days and at its worse it is +/-4M, as for losing satellites, never have.
At night, clear days it is at its best I guess because of the lack of clouds etc, but it never loses the signals, just drops one or two satellites. I can have 9 or 10 at any one time down this part of the world. The more you have the more accurate it is due to the Triangulation theory, but in the case of 8 or 9 it is Octangulation or something....:woohoo:

[Jantar]

No thats not true. You can't assume that an error will be identical between samples. The error range maybe the same but the value and direction will be different every time (though probably not by much in most cases but still different). Errors are due to a combination of factors from atmospheric to bouncing off buildings, not just satellite positioning.

.....

Sorry, but it is true. The causes you mention are the ones that cause satelites to either come into or out of view. Today's technology means that atmospherics are no longer an issue, and 99% of New Zealands roads are not close enough to large buildings to cause satelites to be hidden.

[Hoon]

I beg to differ - most (if not all) are now fitted with the Sirfstar III chip that dramatically improves the usability of GPS's. Cloud, walls, indoors, tree cover, etc interference is pretty much a thing of the past (although they still aren't magic).

I use a Garmin 60Cx which has that chip and yes agree that it way improved over my old GPS12XL. The point I was making is that these conditions are sources of 'reduced accuracy' and in extreme cases can cause 'loss of signal'. Yes the newer chipset greatly reduces this but doesn't eliminate it so as a motorcyclist relying on a GPS for speed calculation you need to be aware that your speed reading will be less accurate in these situations.

Edit: Thanks for putting me onto that chip. Found an interesting article here (http://www.gpspassion.com/fr/articles.asp?id=143&page=1) comparing the different chipsets.


Sorry, but it is true. The causes you mention are the ones that cause satelites to either come into or out of view. Today's technology means that atmospherics are no longer an issue, and 99% of New Zealands roads are not close enough to large buildings to cause satelites to be hidden.

I'm still not convinced, do you have any references to back this 'error is always the same' claim up??. Other than your assumption that no one ever ride past a tall building, most of us have seen the effects of these fluctuations in error when stopped at traffic lights and the GPS showing your position dancing around the intersection. Even now with my GPS sitting on my desk at +-7m I still end up with a spider web track log 10m wide after a few mins . If you're saying that GPS error is always constant then why does this happen?

[Jantar]

..... Even now with my GPS sitting on my desk at +-7m I still end up with a spider web track log 10m wide after a few mins . If you're saying that GPS error is always constant then why does this happen?

Inside a building with a roof that is opaque to radio signals? With limited direct line to satelites and plenty of interference patterns?
Try out in the open and see if it still happens.