View Full Version : Re: Computers on Cokers

July 14th 03, 03:30 AM
chirokid wrote:
> *The computer has no idea where the magnet/sensor are mounted, nor
> does it matter. It can be near the rim or very close to the hub. All
> the computer knows is to count 1 revolution each time the magnet goes
> past the sensor. Hope that helps. If not, I'm sure someone else will
> explain it much better.*

Actually, that helped immensely. I wasn't halfway through reading the
first sentence of your reply when the roar of a gigantic DUH! started
building underneath my desk. Clearly I should have taken fewer trips out
into the woods before my high school science classes. I can't believe I
asked such a stupid question....:rolleyes:

Thanks for the reality check....I'm going to go try my superglue and
washer setup.

tomblackwood - Under-prepared Dork (UPD)

My other brake is my face!

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July 14th 03, 07:35 AM
Actually, the position does matter, but in a way that may not be
relevant. The position inboard/outboard determines the width of the
electrical pulse generated by the sensor at a given speed. The computer
electronics are designed to handle a certain sense of what "pulse" is.
We can't know exactly what that is because we haven't been given the
information with the computer. The optimum placement for the
magnet/sensor, then, is the place which would make it most closely match
the bicycle setup for which it was designed, because this would match
the range of pulse widths most closely. To complicate things, the
instruction manual doesn't state where on the bicycle wheel the sensor
should be placed. However, there are some limitations due to sensor
wire length which govern the magnet's placement. On the Enduro II,
though, there is an internal setting "B" which makes slower speeds, such
as mountain bikes would encounter, more accurate. Presumably this
changes the computer's expectation of what a pulse will look like,
perhaps by changing the sampling rate, or one of many other possible
adjustments to the signal processing.

In short, I'd put the sensor a little farther out than on a mountain
bike, and use the "B" setting. Here's a pic of a sensor on a Coker,
shimmed-out to meet the spokes at the optimal distance.

Placing the sensor at the hub, although a) impossible due to the default
sensor wire length limitation, and b) theoretically counting 1
revolution like any other location, is not desirable simply because it
would lengthen the electrical pulse put out by the sensor so much that
the computer readout most likely would be unreliable. It would make an
interesting experiment to perform, just to see what happened!

| Attachment filename: shimmed sensor and magnet (small).jpg |
|Download attachment: http://www.unicyclist.com/attachment/153261|

U-Turn - Mounting a Revolution

Weep in the dojo... laugh in the battlefield.

'Strongest Coker Wheel in the World'

-- Dave Stockton
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July 14th 03, 08:54 AM
tomblackwood wrote:
> *
> John: I'm not sure if you've tried the setup yet with one of your new
> Schwinns. I purchased the WalMart model, and in installing today, the
> magnet unit definitely doesn't fit over the spoke. What my current
> intended solution is will be to pry the groove on the magnet unit wide
> enough it that it can fit far enough over the spoke to show metal on
> the other side, then superglue a small metal washer or some other flat
> piece to hold it on. If you've already solved the problem in some
> more elegant fashion, would love a tip. *

You are correct there. The slot in the magnet is not wide enough to fit
around the Coker spoke. I just removed the magnet off my Coker to see
what I had done to make it fit. I can see that I had filed the slot to
make the slot wider. I don't have a metal file that thin so I must have
used a fingernail file (emory board) to file it. It's soft metal so it
files easily.

It's a bummer that the magnet doesn't fit the fat Coker spoke without
modifications. One strike against an otherwise excellent low cost cycle
computer for the Coker. I don't remember having to file the slot wider,
but obviously I had done so. The obvious file markings on the magnet
are evidence enough.

john_childs - Guinness Mojo

john_childs (at) hotmail (dot) com
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July 14th 03, 12:05 PM
The pic above is of stainless 14g spokes obtained from Tom Miller, so
the magnet went on with no modifications.

U-Turn - Mounting a Revolution

Weep in the dojo... laugh in the battlefield.

'Strongest Coker Wheel in the World'

-- Dave Stockton
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Frank A.
July 14th 03, 12:37 PM
I went with U-Turn's reccomendation (thanks) and got the Cateye Enduro
II. It went on beautifully with no modifactions at all, just like the
above photo. I didn't know about advantages of using the "B" setting, I
just set it up with the "A". I used the # I got from a seated roll-out.
It's been working great. It adds a nice bonus motivation factor to
The wire is a heavy-duty one and, as I mentioned earlier in the
thread, it only cost 16.99 through Performance Bikes.

- Frank

Frank A. - off-road

"Man's maturity: to have regained the seriousness that he had as a child
at play." - FRIEDRICH NIETZSCHE, Beyond Good and Evil

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July 15th 03, 06:57 PM
The distance from the magnet to the receiver has to be less then a
quarter of an inch.

The way it works is the receiver is a magnetic switch, which means that
every time it passes a magnet it closes, it then closes a circuit. The
computer DOSEN'T measure the speed the magnet passes the receiver it's
just a switch. The computer counts how many circuits, or spins, it
makes in a specific time frame. The problem with that is how dose the
computer know how big every spin is? For that they made the calibration
system, you put in how many millimeters you wheel goes on every spin,
the switch tells the computer every time it spins once, the computer
times the amount of time in between, and out comes the speed. So the
truth is that it doesn’t make a difference where on the spoke you put
the magnet since every time the wheel goes around once the spoke goes
around once.

Now most computers don't have the calibration input for the size wheel a
Coker has, so the solution to that is to tell the computer the total
distance on every spin by dividing up the spin. Meaning you put in half
the rollout distance and put 2 magnets so the computer counts the
distance twice which at half the rollout value is the right speed.

Now to make things simple
Step 1. Buy any computer.
Step 2. Rollout you wheel at proper inflation.
Step 3. Check if you computer goes that high
If it does
Step 4. Set the computer
Step 5. Attach the computer
Step 6. Attach the magnet
Note. The computer and magnet could be at any height.
If not
Step 4. Set the computer at half the rollout distance
Step 5. Attach the computer
Step 6. Attach 2 magnets across from each other (9 spokes)
Note. Always make sure the magnet passes the receiver.

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