bike compass



P

Paul Nevai

Guest
Althoguh my Forerunner GPS has a built-in compass, it is very small and shows
N - NW, etc, only. I want a nice, fancy, and accurate compass for my bike
which is not fooled by the magnetic field generated by my bike. Regular
[magnetic] compasses don't work. I tried about a dozen different models.

The best would be a compass which can be permanently mounted or one which has
a bike mount accessory.

Any suggestions?

Thanks, Paul
 
P

Peter

Guest
Paul Nevai wrote:

> Althoguh my Forerunner GPS has a built-in compass, it is very small and shows
> N - NW, etc, only. I want a nice, fancy, and accurate compass for my bike
> which is not fooled by the magnetic field generated by my bike. Regular
> [magnetic] compasses don't work. I tried about a dozen different models.


If you don't want it to be based on the magnetic field, then a GPS
receiver is your most practical alternative. Most units (Geko, eTrex,
SporTrak, Meridian, etc.) have a display that shows a large compass and
they also can indicate your current course direction numerically in
degrees. [Your Forerunner is an exception with a greatly simplified GPS
feature set.]
But note that the GPS-based compass determines the direction by seeing
how your position changes. So if you stop, the unit doesn't know the
direction anymore.

> The best would be a compass which can be permanently mounted or one which has
> a bike mount accessory.
>


The Foretrex and Geko series are the most compact and they have bicycle
handlebar mounts available.
 
G

G Huang

Guest
Paul Nevai wrote:
> Althoguh my Forerunner GPS has a built-in compass, it is very small and shows
> N - NW, etc, only. I want a nice, fancy, and accurate compass for my bike
> which is not fooled by the magnetic field generated by my bike. Regular
> [magnetic] compasses don't work. I tried about a dozen different models.
>
> The best would be a compass which can be permanently mounted or one which has
> a bike mount accessory.
>
> Any suggestions?


The only compasses that are not fooled by your bike would be good
digital electronic compasses. I use one in my car. It has a calibration
algorithm that computes the correction vectors while you drive around a
circle a few times at a constant speed. You can also specify the local
magnetic declination so that the displayed north is the true north. It
is, however, still a magnetic compass and still subject to being
"fooled" by the surrounding field distortions such as nearby cars, steel
structures, etc.
GH
 
R

Ron Hardin

Guest
Aircraft compasses have a couple compensation magnets, and you
``swing the compass'' by removing half the error by diddling the
magnets repeatedly as you point in known directions. Then you draw
up a table of corrections still necessary (for X steer Y). So that's
about the best you can do with a magnetic compass. Magnetic courses
don't work out anyway owing to wind, so in the end it's just a way
to start and then it becomes a way to hold whatever heading works
after that.

The cheap Garmen eTrex GPS displays course to a degree, if you're moving,
based on position differences. I have two and they generally agree to
a degree, if you're in the open and moving.
--
Ron Hardin
[email protected]

On the internet, nobody knows you're a jerk.
 
P

Peter

Guest
Ron Hardin wrote:

> Aircraft compasses have a couple compensation magnets, and you
> ``swing the compass'' by removing half the error by diddling the
> magnets repeatedly as you point in known directions. Then you draw
> up a table of corrections still necessary (for X steer Y).


You don't need to go nearly so high-end for that feature. Even the
automotive compass I picked up at K-Mart for under $10 has the
adjustable orthogonally-placed compensating magnets. It's not as easy
to adjust as the electronic versions but since the magnetic material in
my car is fixed in place it only had to be done once and it has remained
accurate for quite a few years. Residual errors are only a few degrees
which is not a significant concern for car navigation.
 
M

Michael J. Klein

Guest
On 26 Jun 2004 22:19:37 GMT, [email protected] (Paul Nevai) wrote:

>Althoguh my Forerunner GPS has a built-in compass, it is very small and shows
>N - NW, etc, only. I want a nice, fancy, and accurate compass for my bike
>which is not fooled by the magnetic field generated by my bike. Regular
>[magnetic] compasses don't work. I tried about a dozen different models.
>
>The best would be a compass which can be permanently mounted or one which has
>a bike mount accessory.
>
>Any suggestions?
>
>Thanks, Paul


Paul, I believe that what you want is a flux-gate compass, which is a
lot less suspectible to extraneous fields.


Michael J. Klein [email protected]
Dasi Jen, Taoyuan Hsien, Taiwan, ROC
Please replace mousepotato with asiancastings
---------------------------------------------
 
Z

Zog The Undeniable

Guest
Paul Nevai wrote:

> Althoguh my Forerunner GPS has a built-in compass, it is very small and shows
> N - NW, etc, only. I want a nice, fancy, and accurate compass for my bike
> which is not fooled by the magnetic field generated by my bike. Regular
> [magnetic] compasses don't work. I tried about a dozen different models.
>
> The best would be a compass which can be permanently mounted or one which has
> a bike mount accessory.


Get a carbon fibre frame? ;-)
 
R

Ron Hardin

Guest
Michael J. Klein wrote:
> Paul, I believe that what you want is a flux-gate compass, which is a
> lot less suspectible to extraneous fields.


Magnetic fields are magnetic fields. There's only one, and you measure
it.

Flux gate is already electronic and so is used where electronics has
to read it, as well as where you want to put the compass sensor away
from field-adding metal and carry the indication back to where the
pilot can read it. You could put the sensor in a plastic trailer
I guess.
--
Ron Hardin
[email protected]

On the internet, nobody knows you're a jerk.
 
J

Jee Doy

Guest
>Get a carbon fibre frame? ;-)

How about placing the sensor on top of the plastic helmet? Unless you have a
piece of metal imbedded in the skull (A Beautiful Mind), you should be ok.
That would be a neat thing for the Cateye's and Timex of the world to come up
with.
 

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