Hello and Welcome,
On the last blog post I was working on getting my vintage Schwinn Exerciser working a little smoother and quieter. If you read the post you know I replaced the noisy Speedometer with a quieter one that was a near perfect match. Checking the comments afterwards, one of my regular readers and supporters "Ryan" commented that I would probably repair and re-use the original Speedometer. I laughed to myself when I read it thinking, "What the #@$* do I know about speedometers?" Answer: Less than nothing. But I sure would like to get a look inside of this old speedometer/odometer. Just to see how it is put together. And maybe get a "general idea" of how it works. So reef the sails! Here we go into uncharted waters again!
Above: The bezel and glass are secured to the housing by these metal tabs that are folded over the lip that goes all the way around the face. These tabs will need to be pried up and straightened.
Above: First I turned the mechanism by inserting the small hand screwdriver in the cable receiver as I did to the speedometer/odometer that was seized up in the last post. That is when I heard the noise.
Above: Although this speedometer was not seized up, it did need lubrication in the port hole on the side of the threaded cable receiver post. So I gave it a drop of Easy Lube oil and the sound went away.
along the way (like the odometer). The magnet at the speedometer end of the cable is rotating.
Following Quote is from How Stuff Works "As the magnet spins, it sets up a rotating magnetic field, creating forces that act on the speedcup. These forces cause electrical current to flow in the cup in small rotating eddies, known as eddy currents". I knew that....LTMS Yeah right, I had no idea!
Another quote from how stuff works.
"The eddy currents create a drag torque that does work on the speed cup. The cup and its attached needle turn in the same direction that the magnetic field is turning -- but only as far as the hairspring will allow it. The needle on the speedcup comes to a rest where the opposing force of the hairspring balances the force created by the revolving magnet."
This makes the magnetic field stronger and those eddy currents bigger. And when all this happens the speedometer needle reacts. The faster the speed the faster the magnet spins and the needle reacts to all this accordingly. So when you slow the rotation of the front wheel, the magnet slows decreasing the magnetic field and the eddy currents become smaller and the needle drops. It is sort of like a compass except the magnetic field is created by the mechanism. And the needle reacts to that field similar to how the needle on a compass reacts to the Earths magnetic field. Amazing Stuff!
PS: I was unable to locate a photograph of the inventor of the eddy speedometer Otto Schulze who patented it in 1902. His design (or variations of it) were used in virtually all automobiles until the all-electronic speedometer appeared in 1993. If anyone can locate his photograph Please post it on the face-book page.
This tiny Trek is for someone very special to me and to all who know her. And tomorrow is her third birthday, I hope she likes it!
That`s all I have for now. I`m still trying to figure out what my next project will be. I have a bout 25 projects to choose from. So until next time, Please RIDE SAFE and remember to Always RESCUE, RESTORE & RECYCLE