Just a compass ...

24 Aug 2015 00:44 - 24 Aug 2015 00:46 #1 by OKA in Africa
OKA in Africa created the topic: Just a compass ...
Just before heading onto the continent of lions and elephants I am rethinking a second try to install a compass in the OKA.

I had one installed which could even be compensated. However it did not work properly. Very sad since I'd like a reliable compass for quick directional reference in the bush.

Is there anybody who has a compass installed in the OKA? Which model? Where did you mount it? Whats your experience with it?

Thanks for any input!

OKA in Africa

Thank you and best regards

OKA #327 in Africa
Last Edit: 24 Aug 2015 00:46 by OKA in Africa.

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24 Aug 2015 04:56 - 24 Aug 2015 05:41 #2 by Lang
Lang replied the topic: Just a compass ...
Most cheap GPS have a compass function.

You could use an aircraft standby compass (the little compass all aircraft have usually on top of the instrument panel). They are not expensive, come with a universal mount and can be compensated (never perfectly) for the magnetic anomolies in the vehicle. Without this ability any ordinary compass is useless. There are many small marine compasses which also have this function but they are not heavily damped for vehicle vibration and tend to jump around.

If you are really serious about cross country driving by compass you can never get the correction perfect and you will have to "swing" the vehicle with someone with an accurate prismatic army style compass standing back away from any magnetic interference to get your heading, say every 10 degrees. You will then have to make up a card (these come with the aircraft compasses which have a little bracket to hold them) to give the difference between the real heading from the remote compass and the vehicle compass - the difference changes for every heading right around the circle. I suspect the best you will do on some headings with a vehicle will be about 15 degrees. This means every heading you take up you will check the card and either add or subtract the appropriate degrees from your dash compass to go on the right course.

You will also have to know the magnetic variation for you particular place on earth.

A number of four wheel drives were fitted with a compass and you might be able to get one of those small top of the windscreen panels from a wrecker - early Pajero? - how accurate they are is anyone's guess?

Unless you like the idea of having a compass a $90 Chinese GPS will not only give you a spare GPS but a very accurate compass at all times without any magnetic anomolies!

You could always be really into it and pick up a sun compass like the Long Range Desert Group or Antarctic explorers used but it takes some skill and a couple of minutes to set up for every heading and not much good at night.

Last Edit: 24 Aug 2015 05:41 by Lang.

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24 Aug 2015 08:33 #3 by Hank Onthewater
Hank Onthewater replied the topic: Just a compass ...
Although I don't know the aviation style of compass, I agree with Lang's comments: Can not see much benefit of mounting a compass in the cab: at best you might get a reading that is within plus/minus 10-15 degrees. And the accuracy is different on each course (direction) you travel).
If you want to be more accurate with such compass, you need to:
- know variation of the area you are in
- calculate the deviation for each direction you travel. The deviation error will be very complicated or impossible to correct with all the steel in the OKA, plus the wiring and currents running though it make a large difference as well!
- calculate correct course on each heading
- have a gimballed unit, and the larger the 'card' (centrepiece) the more accurate the reading can be (but do you really want a large 100 or 150 mm unit in front of you?)

For more general compass information see here

The only advantage of a traditional compass is that one is then not dependent on batteries or technology. So by all means have a compass 'on board', that can be reasonably accurate when you walk away from the van. Or another option is to buy one of those binoculars with a built-in compass. But again, only accurate when you step away from car or any steel structure. Then only variation comes into play not deviation.
Here are some examples of Steiner , prices vary from $600 to $3600, but there are cheaper brands. Sorry, I am biased, have one of the Steiners.

I would say to get a radio/DVD player/ GPS unit with a 7 inch screen in the dash, any smartphone, or a handheld GPS: the third option is the cheapest, and all these options are far more accurate and useful than any compass with needle floating in a bed of oil or alcohol.

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25 Aug 2015 03:22 #4 by Tony Lee
Tony Lee replied the topic: Just a compass ...
Slightly off-topic but I used to get a chuckle or three watching newbies try to set up their satellite TV dish. They would follow the instructions slavishly, but never find the signal - until I showed them how to walk 50 metres to the north from all vehicles, take a sighting on a feature on the horizon at the correct heading and then use that point to aim their dish. Close to the vehicle they were often 30 degrees out.


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