Looking along a long straight road amidst lush green farmland

Home Guest Posts

A Motorcycle Compass?

Art Tickle Received 9 September 2020

By Mark Noel

You have spent months planning your first foreign motorcycle journey. By that I mean a trip to foreign parts, rather than a trip on a foreign motorcycle, though both seem likely these days.

With mounting excitement you pack and re-pack the bike with dried food, dried water, Slumit tent, air mattress, inflatable kitchen sink, Aga cooker, Le Crouset pan set, gas bottles, hair styling kit and jerry cans of spare fuel. Oh, and almost forgot, a mirror and flares to signal to the rescue helicopter.

After weary miles through hills and dales, forests and glens, you eventually cross the border and begin searching for that dream campsite suggested by B&T readers. But you are soon lost: the signs are in a language that is weird and unfamiliar, and the battery on your GPS has expired. So you hail a native and seek directions to the night's resting place, but his response is uttered in a strange tongue with twisted consonants and so you motor on cursing the lack of a simple compass to guide you on your way.

Not a good start to your first trip to Wales.

My experience when riding on the Incontinent is that a compass would indeed be a useful navigation aid on a motorcycle. Sometimes you arrive at an unmarked junction where the choice is several roads that branch in the right direction and where a compass would solve the conundrum. A GPS only provides a heading when you are actually underway since it computes the bearing between fixes as you move beneath satellites. Ships are able to obtain the heading of a stationary craft by combining readings from GPS antennae mounted fore and aft but this is not practical on a motorcycle because the available baseline is too short and because of the excess cost and complexity.

A sun compass is workable option but needs GMT, global coordinates and of course the sun to be visible. Even then, who wants to stop and set up a gnomon, record the shadow angle and do the calculations while the traffic builds up behind?

An inertial navigation system incorporating a set of gyros is a precision solution proven on ballistic missiles but the technology in the warhead is too bulky to fit under the saddle even when the nuclear charge has been removed.

I decided to fit a magnetic compass to my Honley 125 to see if such a simple device could be made effective. We need to assess whether it is possible to compensate for errors arising from the presence of the bike itself, and if after compensation the compass becomes sufficiently accurate. There are three interactions that cause errors in the compass:

• The permanent magnetisation of the motorcycle acting as a bar magnet.
• The compass magnet inducing magnetisation in the steel nearest the compass.
• The Earth's magnetic field inducing magnetisation in the bike.

The first two errors are fixed, while the third will vary according to the direction the bike is facing. In this project I assumed that the first effect dominates and can be compensated by placing a permanent magnet in the vicinity of the compass, oriented to produce magnetic fields opposing those from the bike. Any remaining errors in the bearing would then be due to the other two effects.

A miniature 'zipper-pull' ball compass was purchased from Amazon, being the one that had the best reviews (i.e. not sticking) and mounted on the stem of the left hand mirror using 3D printed parts and a length of 4mm OD carbon rod. This configuration placed the compass in a good line of sight and at least 20cm away from the nearest steel parts of the bike.

A small compass on a short length of string designed to be fitted to a zipper pullVarious 3D printed parts, nuts and bolts and the compass ready to mount to the mirror stem

The compensation device comprises a 10 x 5 mm rare earth disc magnet inside a 14mm diameter plastic ball, which fits inside a cavity of a plastic part that mounts on the handlebar. The idea is that an optimum rotation of my 'MagnaBall' can be found such that it will transmit fields to the compass that oppose fields from the bike. The ball is then locked with a spider clamp that is also 3D printed in plastic.

A small ball about 1.5cm in black that contains the magnetA 3d printed handlebar mount with a small ball inside, containing the compensating magnetA computer generated image with a clamp holding the compass and another holding the permanent magnet nearby
The setup, the compass is stuck out from the mirror stem and the compensating magnet is mounted on the bars

Using a quality Silva hiking compass I painted a compass rose on the drive with 8 cardinal points. The Honley was parked in alignment with each of these cardinal points and then without the MagnaBall installed the compass bearings were noted. 

Next the process was repeated with the MagnaBall in place and with it being twiddled iteratively until the minimum error in the bearings was found. This took about an hour! The graph plots the bearing errors with (red) and without (green) the MagnaBall compensator, revolving N > W > S > E > N along the X axis. 

The Honley motorcycle in a chalk circle with various compass points drawn on the circle
A chart showing compass accuracy with and without the compensator

You can see that the worst error without compensation is 37º and with compensation is still large at 33º. However, in the range NW to SE the peak error falls to only 7º. This means that provided I plan a trip that only follows roads with this bearing then the compass can be relied upon, but elsewhere I may be as much as 25º off course!

The upshot of this experiment reveals that permanent-field compensation is not sufficient to provide an accurate compass system and that other measures are required. The answer would be to follow traditional marine practice by adding iron or ferrite balls in another mounting and move these about to provide further compensation for the other effects I have listed. Another solution is to mount the compass on a tall mast (say 5m) that takes it away from the fields of the bike and take a readings via a periscope. I look forward to hearing of another B&T reader who has explored this idea and who provides an account that is even more entertaining than this article.

GPS review? Amazing waterproof navigational aid? Share your ingenuity here.

Reader's Comments

nab301 said :-
Interesting !! Outside of urban areas I tend to use livestock as my compass..
22/09/2020 11:14:33 UTC
Ian Soady said :-
Interesting. I'm not sure the bike "acts as a bar magnet" - it's just a big lump of steel that attracts the compass needle which of course is itself a magnet.

Many years ago I had to go through the centre of Turin on the Commando. Fortunately (a) it was a Sunday lunchtime so traffic was light and (b) I was travelling from east to west so as long as I kept the sun on my left shoulder I was at least travelling in the right direction. Of course this ploy only works when the sun is shining although I suppose in damper climes I could observe which side of the trees the moss was growing (north side).

This did prompt me to fit a compass to my Triumph Tiger - as it had a plastic tank there was no need to box the compass as you did. It was just fitted to the inside of the screen. I did try the compass on a couple of other bikes with steel tanks but with no success. Of course most smartphone GPS systems offer a compass function...

My sadly demised Land Rover Discovery had a compass in the mirror and I find I miss that function in my current car.
22/09/2020 12:30:16 UTC
Ren - The Ed¹ said :-
nab301 - how do you go on when you're in Lincolnshire where most of the fields are filled with arable crops? I wonder if sheep follow the same pattern too. It won't be long before Mark fits a 400kg steer to his bike.

Ian - solar navigation is something I use myself. However being from the grimy gritty disease ridden street of Bolton it is seldom availed to myself locally. As for trees and moss? What are these "trees" you speak of?
22/09/2020 15:58:14 UTC
ROD said :-
Last time I looked paper maps were still available, and provide a good alternative to GPS when battery power is not available.
22/09/2020 20:43:26 UTC
Ren - The Ed¹ said :-
"Map" you say? "Paper"? Wassat then? What is this strange archaic technology you speak of? How do you search for a place? How do you know where you are on this paper device? Who plans the route for you?

I agree ROD, paper maps don't need batteries. I was going to suggest they're not so clever in the rain but then neither are mobile phones and sat navs. There are pros and cons with both systems.

I have railed privately against using digital navigation for some time but I finally gave in during my latest trip. Much as it pains me to say, it made life easier.

22/09/2020 21:04:35 UTC
Mark Noel said :-

The bikes, cars, ships and aircraft do indeed act as a bar magnets because each of their steel components will have acquired permanent magnetisation when cast or forged. The magnetic sum of all these randomly oriented components is not nil but results in a permanent magnetisation.

Also, the compass function in a smartphone or GPS unit uses magnetic sensors which unavoidably also suffer error in the ways I describe.

The simplest solution is to 'swing the compass' as they do on ships and have a tabulated set of corrections to be applied to the compass readings. With an electronic sensor (e.g. fluxgate) this compensation could be applied in a microprocessor and accurate bearings then displayed. This task is way below my project list, after perfecting my HydroBoost water injection system and my world famous Vortex MagnaWheel about which B&T readers were very excited.

I value the suggestions made by former Boy Scouts in response to my article. The wind direction can indeed be gauged by seeing how cattle face or birds perch, while south is evidenced by moss and lichen on old tree trunks. So for now I will be taking a Jersey cow and an oak tree to assist with my navigation.
23/09/2020 11:49:02 UTC
Borsuk said :-
I was going to give some scholarly comments on this but it has triggered my PTSD incurred during my Masters Orals where we are required to swing s compass as part of the exam. Due to the flashbacks and paranoia induced by thisI have eaten my notes during the night to prevent Lord Kelvin’s balls sneaking up on me when I am sleeping and beating me to death with a flinders bar.
23/09/2020 22:33:30 UTC
Upt'North said :-
Ed, just checking, is it me?
24/09/2020 09:42:01 UTC
Ren - The Ed¹ said :-
Probably Upt', probably...
24/09/2020 10:48:22 UTC
Mark Noel said :-
Expanding on Borsuk's comments, I feel that B&T readers need to be aware that 'swinging the compass' is something that sailors do to ensure accurate bearings.

The process should not be confused with 'swinging the lead' which is something that landlubbers do when skiving off work.
24/09/2020 11:34:10 UTC
Ian Soady said :-
But swinging the lead was how sailors actually knew how deep the water was (and the more sophisticated ones smeared the bottom of the lead with tallow so they know what the bottom surface was).

I suspect it gained its current meaning as it was an easier job than heaving halliards, running up ratlines or reefing square-riggers' sails as they rounded Cape Horn.
24/09/2020 13:49:04 UTC
Borsuk said :-
Never understood why why swinging the lead became synonymous for malingering as there is quite a bit of skill in it and it is a heavy beastie to throw far enough ahead of the vessel that it has reached the bottom by the time you come up to it then have to recover again and again for hours. Especially the deep water lead which goes to 100 fathoms.
27/09/2020 01:27:11 UTC
Upt'North said :-
Swinging the lead - A person pretending to work (or claiming to be ill) when he is not.
Pre-modern days, seamen would check the depth of water by dropping
a lead weight, attached to a thin marked rope, to the bottom of a
waterway. Some lazy sailors would take as long as possible about it.
They would swing the lead to and fro several times instead of just
dropping it straight into the water.

So Borsuk me o'd cock sparrow, it would appear it refers to sailors using the role to be lazy, rather than it being an easy role.
This site is an edumicational inspiration. Either that or we should ride more, although at a feels like of 42 Fahrenheit it'll have to wait for another day.
27/09/2020 09:56:08 UTC
Mark Noel said :-
My first job after university was six years working in oceanography, roving over the N. Atlantic where water depths were up to 6km. This was too deep to swing a lead, so we used echo sounders instead!

However between shifts we did manage to swing another type of lead at the bar.
27/09/2020 10:50:36 UTC
nab301 said :-
" Ren - The Ed¹ said :-
nab301 - how do you go on when you're in Lincolnshire where most of the fields are filled with arable crops?"

Ren , I'm Ireland based and I believe the human population here is outnumbered by cattle...
As for maps , It's possible to purchase "Rip and waterproof " maps still.!!
30/09/2020 17:25:14 UTC
Ren - The Ed¹ said :-
Ya'll be fine in Ireland then with the "sat-nav" cows. You do realise since your post I've been looking at cows in fields. I must say as a navigational aid I'm not finding them very helpful, the herds I've seen must have broken internal compasses.
30/09/2020 17:49:46 UTC
Upt'North said :-
I find ya Belted Galloway to be the best Navigational Bovine. Trouble is it's a little bit busy on the front of the bike, what with my weather forecasting seaweed, weather cones and of course the lucky heather.
30/09/2020 18:58:44 UTC
Ren - The Ed¹ said :-
That's OK on a big old Pan Euro but I can't see it working so well on Bogger's C90, perhaps he'll have to make do with a homing pigeon. When it comes to weather forecasting I tend to use a salty sea dog complete with West Country Accent. "Aharrrgggh, Jim lad, the skies be grey and me old bones is achin', there be a storm a-comin'". Of course the West Country accent is an affectation from Disney's Treasure Island but I can't take a Glaswegian sailor seriously at all. Sorry Borsuk.
30/09/2020 19:23:06 UTC
Borsuk said :-
Awa and bile yer heid ya southern pansy.

What fo you need a weather forecaster and compass any way seeing as how the rest of the country has a shoot on sight policy for the denizens of Bolton.

Herself and I escaped from W just before they put the barbed wire around the county. We have fled to Spain in the SPTT. We passed over the Milleu Bridge or what ever you call it. Herself's comment was, why didn't the make it blend in with the scenery, it looks horrible. :-)
05/10/2020 23:39:38 UTC
Upt'North said :-
The Great Escape hey Borsuk.
The French are very proud of that bit of a bridge. There's a museum underneath and coach loads of them turn up to watch videos and see scale models of it. I can verify that it can be very windy whilst trying to cross it on two wheels.
Enjoy Spain. I bet it's warmer and drier than old Blighty.
06/10/2020 08:14:58 UTC
Ren - The Ed¹ said :-
Sharon and I went to see that petite little bridge thing over the Millau valley. Did you know when you are at the visitor centre and look upwards to be impressed with the structural engineering, the wonder, the awe and the magnificence, you get both eyes filled with water? Well you do if it is raining as hard as it was when we were there.

Millau the town is lovely. Big enough to have a few interesting sights, but definitely not a small congested city. The surrounding area is charming too.

06/10/2020 08:25:33 UTC
Borsuk said :-
Deffo an improvement in the weather Up’t.
UK run was wet, France was blooming wet, Andorra was cold ( 4 degrees ) and dry and sunny.
Spain is warm and dry and sunny. amazing what a thousand or so miles can do to the weather.
06/10/2020 21:46:57 UTC
Ren - The Ed¹ said :-
Is it me or does France seem to be wet a lot?
07/10/2020 10:12:36 UTC
Upt'North said :-
I have been very wet in France on many occasions, infact probably as wet if not wetter than anywhere else. I remember my wallet was that wet I was accused of money laundering.
07/10/2020 18:55:30 UTC
Borsuk said :-
We need emojis more than ever Ren. Up’ts comment is worthy of a double face palm.
08/10/2020 09:52:49 UTC
Ren - The Ed¹ said :-
Blinkin emojis!!! You will have to learn to use the English language properly fert express your despair and distraught feelings. You'll have to become eloquent like wot I is :-) DAMMIT!
08/10/2020 10:00:32 UTC
Ren - The Ed¹ said :-
Or you could use the picture option provided
Posted Image
08/10/2020 10:03:21 UTC
Upt'North said :-
Do I detect emoji phobia.
And that was one of my better ones Borsuk.
08/10/2020 13:08:38 UTC
Ren - The Ed¹ said :-
It's cos I is an edumificated smart ass innit. Shakespeare didn't need emojis.

The thing is there's some coding involved and it's not something I've done before. I'll have a look to see what's what but I make zero promises. I do have a funny, perhaps unnecessary aversion to them because of the way they are used and the kind of people who tend to use them a lot. There's whole conversations these days using emojis which essentially takes us full loop back to Egyptian hieroglyphics rather than the 26 letters of the alphabet.

Take a look at the vidoe, if nothing else but to see the future of keyboards but mainly just to enjoy Tom Scott's bodge.
08/10/2020 13:22:40 UTC
Bros Steve said :-
Can't we just continue with sarcasm Ren? Puts tin hat on...
14/09/2021 10:22:17 UTC
Ren - The Ed¹ said :-
Sarcasm? Me!? Ain't nobody sarcastic on here we're all very serious and straight faced. I hope you can continue in the Bikes And Travels tradition by ensuring you always wear a frown. We'll be having none of this happy nonsense.
15/09/2021 08:15:49 UTC
KiwiJeff said :-
Best thread ever Baties I laughed so much I had to stop drinking my medicinal wine. Ren will no doubt delete the thread because he is now guilty of promoting happiness. Keep up the good work!
16/09/2021 12:23:30 UTC
Ren - The Ed¹ said :-
I have failed many many times in my life KiwiJeff. And now it seems I have failed at producing a miserable and uninteresting website too. Thank you so very blooming much for pointing out yet another failure of mine. I shall add it to the very (very) long list.

Maybe I should aim to be a failure.
18/09/2021 21:03:55 UTC
Bogger said :-
At least you've succeeded at being a failure, which could be construed as being a success. I think

19/09/2021 14:12:51 UTC

Post Your Comment Posts/Links Rules



Add a RELEVANT link (not required)

Upload an image (not required)

No uploaded image
Real Person Number
Please enter the above number below

Home Guest Posts

Admin -- -- Service Records Ren's Nerding Blog