Eddy Cup Tachometer

Measurements Project

Summary :

The Drag Cup Tachometer is a non-contact rotational speed measurement device that operates using eddy currents and electromagnetic induction. Designed for high-speed RPM measurement, the system provides both analog and digital readouts, making it an efficient and cost-effective alternative to traditional contact-based tachometers.

During this project, I collaborated with a team, focusing on mechanical design and electronics implementation of the Digital to analog conversion. The video includes a presentation and demo.

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Project Overview

What?

Design a Non-contact, device that Measures rotational speed using eddy currents.
Capable of measuring high-speeds using analog and digital readouts.
Optimized for low-cost and manfacturability.

How?

Measured torque from eddy current onto a calibrated 3D printed hairspring to calculate rotational speed.
Utilized an ESP32, potentiometer to measure angular displacement and display speed on OLED display.
Designed dial guage to match angular displacement of needle inicator to output RPM.

Results

Achived succesful employment in high RPM ranges (1200- 8000 RPM) with accuracy of ±50 RPM on digital display, limited by the 10-bit ADC onboard the ESP32.
Dial guage accuracy of needle indicator was ±100RPM.
Achived low-cost production, total tachometer cost $20.

Mechanical Model

Specifications

Working Principles

1. Eddy Currents & Torque Generation

When a rotating magnetized rotor spins near the conductive drag cup, eddy currents are induced in the cup due to Faraday’s Law of Electromagnetic Induction.
These currents create a secondary magnetic field, which interacts with the rotor’s field, producing a braking torque on the drag cup.
The braking torque is directly proportional to the rotational speed of the rotor.

magnet

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2. Torque-to-Rotation Conversion

The drag cup is connected to a spring-loaded needle mechanism.
As the rotor speed increases, the braking torque deflects the needle along a calibrated scale, displaying the RPM.
The hairspring restores the needle to zero when the rotor stops, ensuring repeatability.

3. Digital RPM Measurement

To obtain a digital RPM readout, a potentiometer sensor is attached to the needle mechanism.
The potentiometer converts angular displacement into an electrical signal, which is processed by an ESP32 microcontroller.
The ESP32 maps the sensor voltage to a calibrated RPM value and displays it on an OLED screen.