![]() average the two numbers, and this is the real number. If there was really no wind, it should be the same reading, but if there was 1 or 2 MPH wind, you should get readings a little apart. Then go the opposite way and check the meter. Have your friend drive the car at exactly 20 MPH in one direction, and record the reading on the meter. The easiest way to calibrate is to get a friend and go driving in a car on a day with no wind. The bike speedometers have an adjustment in them for different sized bike wheels, and this will give you enough flexibility to get a convenient multiple like 3 or 4 or 5. So if my meter says "60", then it's really 20 MPH wind. Instead you'll have a reading which is a multiple of the actual speed. now the shaft should be locked onto the assembly, and spinning freely, and the speedometer should work when you spin the cups! almost done! attach the speedemeter to the block, or else attach the block and speedometer to a handle or rod of your choice, and tie down the wires.Īll you need to do now is calibrate! What I found is that most bike speedometers won't have the correct range to display actual MPH / knots / KPH. now put the spacer on the other end of the shaft, and put a bit of glue on to glue the spacer to the shaft (no glue near bearing!). Make sure not to get glue in the bearings! The wind cups have a very tiny set-screw in the side, tighten up the set screw to lock the cups to the shaft, and push the cups and spacer snug against the top bearing. Once you've found a setup that works, attach the switch in that position (use silicone glue because then if you botched it you can pull it apart later and re-do it). Magnet is too close and the magnet never gets far enough away to disactivate the switch.Magnet is too far, and never activates the switch.The pole of the magnet in the wind cups is at the bottom, so the magnetic switch needs to be under the wind cup hub, not at the side of it. You'll need to play around with the distance and orientation a bit to get it right. You need to attach the magnetic switch to the top of the block right under the wind cups so that it is activated by the magnet on the spinning wind cups. The exact distince will depend on how big the magnetic switch is. At one end the spacer goes between the bearing and the wind cups in order to hold the wind cups away from the block about 1/2" or so. You will need to put a spacer at each end of the shaft, right next to the bearings. basically just little metal tubes with an ID of 1/8 inch and OD of maybe 3/16". These you can get at the hobby shop or at a hardware store. The speedometer detects the open-close-open of the switch, and speed is computed by how often the switch is activated.Īt this point you will need some spacers/collars which fit over the shaft. Every time the magnet on the spinning wheel passes the reed switch, the switch pops closed and then open again. On a bike, you attach a magnet to one of your front wheel spokes and then you attach the reed switch to the front fork. It's quite convenient to use a bike speedometer here, because they detect bike speed using a magnetic reed switch. I've tried a couple designs out of cut-up beer cans and soda bottles, but have not gotten anything that works well enough. In a future version of this project I hope to make my own wind cups. They have a photo on-line of their entire wind-assembly, the wind-cups you'll be getting are just the piece at the bottom of this assembly. The hub has a 1/8 inch hole for a shaft, and it has a magnet embedded in it for use with a magnetic reed switch for detecting rotation. Anyway, the wind cups are a nice plastic assembly, about 6 inches in diameter with three cups attached to a central hub. The wind cups we are using are considered "replacement parts", you might need to tell them you have one of their weather station products but you broke the wind cups. So if you'd rather just buy a nice anemometer, i'd highly recommend theirs. This is a significant time-saver over constructing your own wind cups! Davis sells anemometers and weather stations, their complete devices cost around $200 i think. Notes on the parts: For the Anemometer head we use the "wind cups" from Davis Instruments. Bike speedometer from any bike shop 2 ball bearings, 1/8" ID from any hobby shop (used in radio control models) Once you have the parts, this project should take less than three hours to construct I think. Major parts needed: Wind cups, part #7903 from Davis Instruments (cost around $15.
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