Re: 55 Patrician Speedometer

Posted by HH56 On 2024/2/10 20:53:47

There is a spinning magnet on the end of the piece the cable turns in the bushing. It does not touch but rather spins around on the inside or outside of a spring loaded aluminum cup which is attached via a shaft to the needle. The spinning magnet sets up an eddy current around the cup which will try to drag the cup along with the magnet thus moving the needle. As long as the magnet spins consistently and smoothly the calibrated but light spring loaded cup and needle responds appropriately -- faster the rotation, stronger the eddy current force so higher the needle will move against the spring. If the magnet spin is erratic because of a dry bushing or a problem with the cable and magnet stops and then suddenly jerks with a quick and fast motion as something breaks free the cup reacts violently. That action can slam the needle into a stop and because the cup is a relatively heavy mass and the point where needle is pressed onto the shaft is very small the joining point on the shaft can break as the needle suddenly stops and often will twist off.

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