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Subject: Re: Dunce question
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Date: 02/28/03 at 10:57 AM
Posted by: Brian Snell
In Reply to: Re: Dunce question posted by andrew on 02/27/03 at 5:38 PM:
Hello again Andrew.
Good news about the tacho feed -- this would be fine with some additional simple filtering in case there are odd unwanted glitches.
Now, as far as the output goes, can you take a look at the speedometer "take-off". I presume that this is some form of worm drive integrated to the output somewhere inside the gearbox and is fed to the speedo by a flexible cable inside an outer sheath. The gearbox manufacturer should be able to advise the gear-ratio (speedo rotations per output-shaft rotations). What would be great would be if this cable sheath (at the speedo end) could be re-worked to provide access to the internal driving cable but external to the speedo casing, so that a timing disc could be inserted.
I don't want to get too tied up with the detailing of this as it is a local problem the methodolgy for solving which is for you investigate. I can see the sheath terminating at a metal plate which is the mounted to the speedo case by three extension posts spaced far enough apart so that the timing disc diameter can rotate freely. Alternatively, a driving gear could go there and be coupled to an external commercial encoder. Rather than cutting and shortening the sheath you could use a longer inner cable to accomodate the extension length required. If you want to keep costs down (who doesn't) you could make your own timing disc and use a simple IR slotted optical switch for the pickoff. As yet, until you can find out the speedo ratio I cannot confirm the minimum number of encoder holes.
Let me know what is what when you have had time to digest all this.
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