Stream flow meters are expensive, so we made our own and calibrated them with the very expensive magnetic induction flow meters. Our stream flow meters were made using model boat propellers and bike odometers. When calibrated, these meters yielded results that were within 5% of the magnetic flow meters results.
Step 1: Materials
1 meter, 3/4" thick wall aluminum tubing 25 cm 1/2" thick wall aluminum tubing
model boat propeller 1" diameter
bike odometer ( inexpensive)
1/8 " rare earth magnet
1.5" plastic disk
1/8 stainless threaded shaft ( for model boats)
Step 2: Construction of the Handle
Drill a 1/2" hole through the center of the 3/4" rod at 6 cm from the end. This should be perpendicular to the 3/4 rod. Drill a 3/8 hole half way through the 3/4 rod at 3 cm above the 1/2" rod. Push and epoxy a 5 cm by 3/8 (OD) rod into this hole. This will be location of the signal pick-up.Push the 1/2 rod through the 1/2" hole so that about 19 cm sticks out the side of the 3/4 tube.
Step 3: Setting Up the Propeller Shaft
Drill a 9/64" hole through the 1/2" plastic plugs then push and glue the plugs into both ends of the 1/2" Al tubing. Slide the 1/8 stainless rod through the holes, (this should be freely moving).
Step 4: Installing the Propeller and Pick-up
Drill an 1/8 hole into the side of the plastic disk and glue a 1/8" x 1/4 rare earth magnetic cylinder into this hole. Slide and glue the plastic disk onto the non-threaded end of the stainless rod. Screw and secure the propeller onto the end of the shaft. Thread the computer pick-up through the 3/4 rod and 3/8 rods and epoxy in place.
Step 5: Installing the Bike Computer and Calibrating
Attach the bike computer on the top of the 3/4 rod and plug into the pickup. Spin the prop and check to see if the movement is recorded on the bike computer.
Calibration needs to involve another flow meter. This involves determining the flow rate with the standardizing meter the adjusting the bike computer to match the velocity of the stream. This will require a number of successive trials.