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Introduction

In today's article, we will see the first test with a new motor design.

This design has the following main objectives:

1. Modularity: for prototyping purposes, it is important that the main mechanical components of the motor (rotor and stator) are interchangeable, facilitating and expediting the testing of new ideas.
2. Compactness: in this design, the use of materials is reduced, making the motor more compact and lighter.
3. Cost-effectiveness: with the reduction in the quantity of materials, especially coils and magnets, the cost of the motor is considerably reduced.

In a future article, I will share the 3D printing files of this new motor. I am still iterating on the design and making some adjustments.

Test 1 - Push-pull circuit

Today, we will test a different topology from the previous ones. This topology has interesting characteristics:

• It can be used as an alternative to an H-bridge, using only 2 electronic switches.
• The motor power control is achieved by sizing capacitor C1 (explained below).
• The motor is not self-starting. An additional mechanism is required for that purpose.

Test environment

The test setup consists of the motor and a 30 cm diameter propeller.

For this test, a 6-blade propeller will be used. This propeller can move more air and consequently has slightly higher electrical consumption compared to the 3-blade propeller used in previous tests.

Control circuit

The circuit used in this test employs a push-pull topology.

Schematic

The figure below depicts the control circuit. The switching sensor can be an optical sensor or a Hall sensor. For this test, we will use a Hall sensor.

In this topology, two sensors are required: one for each pulse direction.

Operation

The circuit works as follows:

1. When Q1 is biased, current flows through L1 until C1 becomes fully charged. This creates a pulse in one direction (pull).
2. When Q1 is biased off, the current stops flowing through L1, and a voltage spike appears at the connection between Q1 and L1. This pulse is directed to the ground (GND) through the reverse current diode of the MOSFET itself or a fast diode added for this purpose.
3. Now it's time for Q2 to be biased. When this happens, the energy stored in C1 flows through L1 in the opposite direction, generating a reverse pulse (push).
4. When Q2 is biased off, the same thing happens as in step 2, but in the opposite direction.

Since C1 controls the charging and discharging of the pulse, its size determines the motor's power. However, it should be sized according to L1:

• The smaller the inductance of L1, the larger the capacitance of C1 should be.
• The larger the inductance of L1, the smaller the capacitance of C1 should be.

Motor

Electrical characteristics:

• Resistance (Ohm): parallel: 2.3 / series: 8.9
• Inductance (mH): parallel: 1.0 / series: 4.27
• Amount of aluminum used in the motor (Kg): 0.090
• Wire thickness (AWG): 22 (bifilar)

This motor was designed to operate with voltages between 9 and 36VDC (depending on the coil arrangement).

Results

The results are shown for coil configurations in series and parallel.

Power x speed

Bifilar in series:

Capacitor(s) used: 1x 63V/1000uF.

Bifilar in parallel:

Capacitor(s) used: 2x 63V/1000uF.

Final considerations

The results are quite satisfactory, especially considering the amount of wire used in the coils. Comparing with previous tests, there has been a reduction of approximately 35% in material.

The higher number of poles (6) makes the pulses shorter, reducing waste of charge in the coil.

The topology used also helps to minimize waste, although I have achieved similar results using a traditional H-bridge configuration.

Regarding the number of magnets used, there has also been a reduction of approximately 10% in the total weight.

Questions?

If you have any questions, feel free to contact me.