Thrust Calculator

About: I am a student studying engineering. Although I study mechanical engineering, I equally love electronics and electricity. I hope to post a few more of my projects and would be happy to help if you get stuck.

In this project I will describe how I made a setup which monitors the Voltage, Current, the thrust developed by the propeller and the speed of the motor. The system cost me very little to make and works flawlessly. I have added a excel sheet which contains data for the fist successful run. I have also added graphs as they describe the data in one go. Hope you like the project and if there is any confusion or any question or suggestions please comment below or message me.

I have added a detailed document of a very similar project I had done before. Download that for even more details

Supplies in addition to your ESC and Motor-

  • Perf board
  • Shunt reistor
  • LM324
  • Wires
  • Wood
  • Hinge
  • Arduino

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Step 1: Making the Thrust Sensor

Thrust sensor at its basic is just a force sensor. The most popular way of measuring force is to use a load cell. I however, decided to go a bit old fashioned and I developed my own sensor. This was particularly possible for me because I got myself a 3D printer recently and hence making custom parts was not an issue.

The sensor has two main parts, the spring and the sensor. The spring as we all know will give displace by an amount proportional to the force applied on it. However, it is very difficult to find a small spring with right stiffness and size and even if you find one, it is another nightmare to set it up properly and make it work just the way you want it to. So hence I completely replaced the spring with an aluminum strip, 2 mm in thickness and around 25 mm in width.

The the cantilever beam should be held very firmly on one end or the values will go wrong for sure. I also made a special attachment on the other end so that it is easy to couple to the rest of the system.

The cantilever beam was then attached to the linear sliding potentiometer by a coupling rod which was also 3D printed.

I printed all the coupling holes a little smaller than the thread diameter of the screws I had so that there is zero play in the system. The potentiometer stand was also 3D Printed like the rest.

Step 2: Speed Sensor

One of my major inventions of my life time (till date) is the speed sensor intended to measure the angular velocity of any device. The heart of the system is magnet and a hall effect sensor. When ever the magnet crosses the hall effect sensor the output falls low. This requires a pull up resistor between output and the 5V line. This job is done by the arduino's internal pullup resistor. The magnets are arranged on a ring at two extreme poles. This helps in balancing the weights of the system. The hall effect sensor is placed in a dedicated slot which was 3D printed. The stand is so designed that the height and the distance can be adjusted.

When ever the magnet is near the hall sensor, the output of the sensor goes low. This triggers the interrupt on the arudino. The trigger function then makes a note of the time.

Knowing the time between two crossings one can easily determine the angular velocity of any rotating body.

This system works flawlessly and I have used that in another project of mine.

Step 3: Voltage

This is basically to measure power consumed by the esc and hence the motor. measuring the voltage is the easiest thing that one learns when using arduino. Use analog pins to measure any voltage upto 5 V and use a voltage divider for any voltage higher than 5V. Here the conditions were such that the battery could reach a maximum voltage of 27 ish volts. So I made a voltage divider to make a divider that delivers 5 volts under a supply of 30 V.

Also be doulble sure that you don't accidentally short the + and - lines which may easily result in fire.

Step 4: Measuring Current

Measuring current or handling current in any form requires knowledge and experience of what you want to do. The shunts I used were four .05 ohm 10W resistor. This means that they can handle a current of (P/R)^.5 = (40/.0125)^.5 = 56.56A. This was more than enough for me.

Be sure to make thick solder traces and use thick wires when dealing with such large currents. Have a look at the back of my circuit especially in shunt region were super thick wires are used.

It is also important to use some low pass filters in combination to the shunts. I have added a picture of the current draw of the ESC as measured by my DSO138. This is a very big mumbo jumbo for arduino to process and hence a passive filter would mean a lot to arduino. I used a 1uF capacitor in combination with a 100k pot to make the filter.

Please please contact me if you have any doubts in this section. This may destroy your battery if not done right.

Step 5: Upload the Program and Make Connections

  • OUTPUT OF HALL EFFECT SENSOR = D2
  • OUTPUT OF FORCE SENSOR'S AMPLIFIER = A3
  • OUTPUT OF VOLTAGE DIVIDER = A0
  • OUTPUT OF CURRENT AMPLIFIER = A1

The first row in the program is time in seconds. It is important if you want to measure acceleration or anything time dependent.

You're all done here and now collect all types of data form your new new device.

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