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| czakal |
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czakal
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spyuggy
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kerr
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Kickstart
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 Posted: 22:48 - 16 Oct 2011  Post subject: |
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Hi
Digital isn't likely to be any more accurate than analogue.
However a speedo running off electronic pulses (so pretty much all digital, but also quite a few more modern analogue ones) is easier to recalibrate.
If it is a cable operate one from the front wheel then it isn't really an easy job to recalibrate it (no doubt can be done by specialists).
Probably just easier to connect up a bicycle speed as well and calibrate that carefully, or mount a GPS unit on the bars.
All the best
Keith
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czakal
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| The Artist |
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The Artist
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Kickstart
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czakal
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| Teflon-Mike |
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Teflon-Mike
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| Posted: 21:26 - 17 Oct 2011 Post subject: |
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| czakal wrote: | Thanks for the quick replies. I'll consider the GPS option as I'd been thinking of it for a while (a half decent one might end up costing half as much as the Kymco...). How accurate are those? |
Well, I have a pretty high spec GPS marine GPS reciever to plug into my lap-top, and you can get silly looking at the specs of them and the number of satalite locks they can read from at any one time, and thier sampling frequencies etc, and then the data-protocol that they send it to 'processing device' via... Ultimately the possitioning accuracy of my marine sender is greater than the plotting accuracy of most maps I use, and I have pretty high resolution OS maps for land use!
Snail-Trailing off Snowie's little GPS, if the track is within a lines width of the road, you are doing pretty well, but the Marine senders snail-trails aren't often much closer to the chart beneath them.
As for speed, well, my marine sender has told me my window sill was walking around my block at 4mph...... and that's an 'accurate' one......
Reason is down to the fact that on my windowsill, can probably only 'see' one or two satalites in the bit of sky between the houses.
this is called 'urban canyon' effect. Had similar issues in valleys in wales, between the mountain sides, and reciever location to maximise sky-view really makes a big difference.
For ALL they 'hype' that they 'can' be accurate to within a diameter of a few metres, that is still not all THAT accurate on a real road, which might only be two meters wide..... pretty damn accurate on a global scale, when you think they are measuring things over thousands of miles, down to a couple of meters..... but still.
Generally they are accurate 'enough'. The gps recievers in proprietry sat-navs are not hugely sophisticated, nor the most accurate, but they are 'adequete' and difference in hardware between them and higher end recievers doesn't make them that much better in real woirld situations where you get Urban canyon effects, or you are in satalite cross-over areas.
In a car, conventionally sited in the front widscreen, thier 'sky-view' is atrociouse, the car's body often masking anything up to 80% of 'sky view'.
Mimicking it with the Marine sender, I have placed it on teh roof of my car and got twelve 'good' satalite locks with strong signal strength; bringing it inside the car and putting it on the dash-board, where a SAT-Nav would wit, dropped to three. That was in Honda Civic with quiite steeply sloping windscreen, giving a fair proportion of sky for it to see. Same test in my Range-Rover, with almost vertical windscreen, twelve sat-locks outside the car, inside on the dash, was getting no aquesition error or a very weak signal off just one or two sats, not enough to get a 'fix' from.
Speed calculations are based on comparing position data to measure distance traveled, against time base... way GPS works, means that there is a lot of room for calculation error.....
Possibly MORE than for empirical metrology, counting wheel turns as a mechaincal system driven from the front wheel.
However, most automotive speedo's are 'calibrated' to over read, and 10% + 2 isn't far off.
Speedo in the Chavic over reads against GPS by aprox 10%, on a clear open motorway, in 'flat' terrain, where both have nice stable reading.
Through town, GPS can get rather erratic due to canyon effects, and stop-start traffic conditions; and driving round Leicester inner ring-road, the radio interference caused by a metal clad department store (think it was John Lewis's or Debenhams) had both marine receiver and sat-nav in utter apoplexy as I approach it, then shutting down in disgust in the actual 'hot-spot' of radio reflection!
So, its a matter of 'accuracy' and 'reliability'.
GPS can be pretty accurate, but its reliability is in more doubt, depending on receiver positioning, and geographic circumstances.
Mechanical speedo, much more reliable; measuring off the front wheel, only thing that really effects it is tyre wear; but the accuracy is often not so 'close' on, to begin with.
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| LordShaftesbu... |
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LordShaftesbu...
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| Posted: 11:28 - 20 Oct 2011 Post subject: |
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| Teflon-Mike wrote: |
Well, I have a pretty high spec GPS marine GPS receiver to plug into my lap-top, and you can get silly looking at the specs of them and the number of satellite locks they can read from at any one time, and their sampling frequencies etc, and then the data-protocol that they send it to 'processing device' via... Ultimately the positioning accuracy of my marine sender is greater than the plotting accuracy of most maps I use, and I have pretty high resolution OS maps for land use!
Snail-Trailing off Snowie's little GPS, if the track is within a lines width of the road, you are doing pretty well, but the Marine senders snail-trails aren't often much closer to the chart beneath them.
As for speed, well, my marine sender has told me my window sill was walking around my block at 4mph...... and that's an 'accurate' one......
Reason is down to the fact that on my windowsill, can probably only 'see' one or two satellites in the bit of sky between the houses.
this is called 'urban canyon' effect. Had similar issues in valleys in wales, between the mountain sides, and receiver location to maximise sky-view really makes a big difference.
For ALL they 'hype' that they 'can' be accurate to within a diameter of a few metres, that is still not all THAT accurate on a real road, which might only be two meters wide..... pretty damn accurate on a global scale, when you think they are measuring things over thousands of miles, down to a couple of meters..... but still.
Generally they are accurate 'enough'. The gps receivers in proprietary sat-navs are not hugely sophisticated, nor the most accurate, but they are 'adequate' and difference in hardware between them and higher end receivers doesn't make them that much better in real world situations where you get Urban canyon effects, or you are in satellite cross-over areas.
In a car, conventionally sited in the front windscreen, thier 'sky-view' is atrocious, the car's body often masking anything up to 80% of 'sky view'.
Mimicking it with the Marine sender, I have placed it on the roof of my car and got twelve 'good' satellite locks with strong signal strength; bringing it inside the car and putting it on the dash-board, where a SAT-Nav would wit, dropped to three. That was in Honda Civic with quite steeply sloping windscreen, giving a fair proportion of sky for it to see. Same test in my Range-Rover, with almost vertical windscreen, twelve sat-locks outside the car, inside on the dash, was getting no question error or a very weak signal off just one or two sats, not enough to get a 'fix' from.
Speed calculations are based on comparing position data to measure distance travelled, against time base... way GPS works, means that there is a lot of room for calculation error.....
Possibly MORE than for empirical meteorology, counting wheel turns as a mechanical system driven from the front wheel.
However, most automotive speedo's are 'calibrated' to over read, and 10% + 2 isn't far off.
Speedo in the Chavic over reads against GPS by aprox 10%, on a clear open motorway, in 'flat' terrain, where both have nice stable reading.
Through town, GPS can get rather erratic due to canyon effects, and stop-start traffic conditions; and driving round Leicester inner ring-road, the radio interference caused by a metal clad department store (think it was John Lewis's or Debenhams) had both marine receiver and sat-nav in utter apoplexy as I approach it, then shutting down in disgust in the actual 'hot-spot' of radio reflection!
So, its a matter of 'accuracy' and 'reliability'.
GPS can be pretty accurate, but its reliability is in more doubt, depending on receiver positioning, and geographic circumstances.
Mechanical speedo, much more reliable; measuring off the front wheel, only thing that really effects it is tyre wear; but the accuracy is often not so 'close' on, to begin with. |
Yeah I though speedos over-reading by about 10% was the norm?
Also, how does he know the instructor's speedo is more accurate? |
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Kickstart
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McFlufferson
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ClockworkJesu...
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Old Thread Alert!
The last post was made 14 years, 174 days ago. Instead of replying here, would creating a new thread be more useful? |
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