Rotor Meter - Measure Flow Velocity of Water

Hello and welcome to this instruction guide to build a sensor that can help you measure the speed of water. This sensor was made for a project of the minor 'Delta Expert: water for the future' from the TU Delft. For this project, we built a sensor that indicates water speed through a spinning propeller that displays its RPM on a LCD screen. My project group member and I had fun building this and hope you'll enjoy it as well!

The following supplies are needed in order to build the sensor that we build:

1. 2 meter of PVC tube with a diameter of 32 mm
2. A 90 degree PVC cornerpiece with a diameter of 32 mm
3. Two Y-Shaped PVC pieces with a diameter of 32 mm
4. A T-shaped PVC piece with a diameter of 32 mm
5. A pair of 5x5x5 mm Neodymium magnets
6. An Arduino Uno
7. A breadboard
8. 49E Hall magnetic sensor
9. 16X2 LCD module
10. Sufficient wiring cables to connect the 49E Hall sensor and 16X2 LCD module to the arduino via the breadboard
11. A 3D printed propeller, this was designed in Solidworks. This .STL file is given in the attachments of step 2. Note: you will need access to a 3D printer in order to make the propeller.
12. Duct tape to attach the 49E Hall sensor to the window.
13. Some pieces of Lego: an axle to connect the propellor and two wheels to attach at both sides of the PVC tube.
14. The Arduino software that is available through their website.
15. Something heavy to make sure the sensor does not float backwards when the water speed gets higher

Note: these sizes are dependent on the water tunnel that you have access to. In our case (the waterlab at the TUDelft Faculty of Civil Engineering and Geosciences) the tunnel has a width of 20 cm.

To start off, 3 tubes need to be cut-off the 2 meter long PVC tube using a pipe cutter. The water tunnel that we are going to use has a height of 40 cm. This means that you'll need to cut two pieces of tube of 40 cm and 1 piece of tube of 56.56 cm (the hypothenuse of the triangle, according to Pythagoras Theorem).

If that is done, you can connect the three tubes using the connecting pieces: the 90 degree corner piece and the two Y-shaped pieces. In this way you will create a triangular structure where the opposite side of the triangle is the side of the triangle that will face to where the water is flowing from.

Next, you need to attach the T-shaped piece to the top of the structure and cut two small pieces (one of 70 mm and one of 130 mm) of PVC tube and place them inside this T-piece. By doing this, you can place the upper part of the structure on the edges of the water tunnel.

If everything went well, you will now have the triangular structure as can be seen in the picture (please ignore the attachments for now).

This propeller was designed in Solidworks and is based on several references from Thingiverse (accessible through: thingiverse.com). The propeller has a diameter of 10 cm (= 100 mm) and can be connected to the structure through a Lego Axle with a width of 4 mm. I'd like to thank Olivier Estourgie for making this creation possible in Solidworks. The 3D printer that we used accepted files in .STL form, therefore, this file is uploaded in this format as well.

During the design of the propeller, we kept the placement of the magnets in mind. Therefore, two square holes were made in the outer ring of the propeller of 4.95 x 4.95 x 4.95 mm in which the magnets can be clamped. We placed two magnets on the propeller instead of one, because then the weight is uniformly added to the structure.

Now it is time to attach the propeller to the triangular structure. Therefore, you need to drill a hole in the structure with a diameter of 4 mm, such that the Lego Axle can go through this hole. The vertical placement of the propeller is dependent on whether you want to measure flow velocity at the water surface, at the bottom or inbetween. We chose to place the propeller at a low point, which ensures that there's always water flowing through the propeller.

The 49E hall sensor needs to be connected with 3 pins. The convention used here is that you need to look at the side of the Hall Sensor that has text on it. Then, the left pin needs to be connected to 5V, the middle pin to GROUND and the right pin to A0 (we make use of analog readings). The LCD module needs to be connected with 4 pins. From top to bottom: Pin 1 to GROUND, Pin 2 to VCC, Pin 3 to SDA or A4 on the Arduino Uno and Pin 4 to SCL or A5 on the Arduino Uno. This is all visualized in the schematic drawing of the electrical circuit that was made by Clockatronic (accessible through: https://www.youtube.com/watch?v=pIflB4FQpNE).

The code that we wrote to command the arduino can be found in the attachments. In order to have an indication of water speed, we count the RPM of the propeller. To do so, we make use of the fact the Hall Sensor can detect a magnetic field and changes in it. Therefore, everytime a peak is detected (when one of the magnets swoops by the sensor) we add this to the count. By counting the number of peaks for a certain measurement time, something about the angular velocity of the propeller can be said. A visual demonstration of the peaks that the Hall Sensor detects can be seen in the picture. After the measurement is taken, we calculate the number of revolutions it would do in one minute (RPM) and display it on the LCD screen. After a calibration in our water tunnel, we then decided on certain RPM ranges and the LCD screen will then also give an indication of LOW, MEDIUM and FAST depending on the calculated RPM.