Application Notes 1 : Speed Control for Stepper Motor

Application Notes 1

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Hardware Development and Prototype

After we purchased the unipolar stepper motor, the school provide us again one bipolar stepper motor. As a result we decided to compare the performance between the unipolar stepper motor and bipolar stepper motor.

Construction of the racing cars body is by using aluminum and plastics. There are only three tyres to each of the design. One tyre is controlled by the stepper motor and the others for balancing the car. Racing car using the unipolar stepper motor constructed using plastics. The basement of the car was obtained from ordinary toy car. We implemented the readymade basement to our design by doing some modification. Circuitry of the design was placed on top the basement. The dimension of the car is 25cm in length and 10cm in width. Height of the car model is 6cm, without the circuit install in the car design.

Body of the bipolar racing car was build by using aluminium. It is constructed by hand. Same concept as the unipolar motor, there are only three tyres in the design and the circuit was placed on top of the basement. The car model gain power from battery source. The length of the model is 20cm and width is 10cm. Height of the car model is 18cm.

Structure of car control using unipolar stepper motor

Structure of a car control using bipolar stepper motor

The casing of remote control consists 3 push buttons (forward, backward and reset), one potential meter (adjust speed) and one toggol switch (on and off).

Casing of remote control

Problem Encountered

In the combining everthing that we discussed in previous posts, there are some features was modified or eliminated as we encountered some problems. There are two features that we modified which are radio frequency module (RF) and encoder.

The radio frequency signal is totally eliminated from our design. We are using wire cables instead of wireless. The reasons we eliminate the feature is the signal in the RF is interphasing with the other group frequency. Most of the other groups are using the same model of RF with the same frequency (433MHz). Distortion of information produced and consequently the data received or transmitted is not the acquired signal. In the design, the functionality of RF is very important. If the RF is not working properly, the design will become a big failure. Another reasons we give up for RF is protocol. The pre-set method to transmitter and receiver cannot applied in the our control car because the value of speed changing time by time. Therefore, the probability the receiver receive the wrong data is very high. As we discussed among the team members, we are not willing to take any risk, so we change the RF to the wire cables. Furthermore, the main purpose of the project is to build test board to stepper motor.

The second feature that we modified is the encoder, speed calculation. As we proposed, the encoder should detect the speed of the stepper motor. Unfortunately, the encoder that we are using was broke during the installation part. Because of time limiting factor, we modified the calculation speed mechanism. Microcontroller itself calculates the rotation of the stepper motor. Data collected from the test done in lab to come out with speed and torque equation. This equation is programmed in the microcontroller. Referring to this equation, the speed calculated.

Technical part 3.0 : Motor Driver of stepper motor

Motor Driver of stepper motor, SD02B

SD02B is designed to drive unipolar or bipolar stepper motor. The board incorporates most of the components of the typical applications. With minimum interface, the board is ready to Plug and Play. Simply add in power and a few push buttons, this driver is ready to drive unipolar or bipolar stepper motor. SD02B will actually drive stepper motor in bipolar method. However, since unipolar stepper motor can also be used as bi-polar stepper motor, thus this driver can be used to drive both unipolar and bipolar stepper motor. This stepper motor driver has been designed with capabilities and features of:

• Now comes with UART interface for easier communication between the user’s circuit and SD02B. By using the new UART control, user can

-On/Off, Run/Brake and change motor’s rotation direction
-Set motor speed
-Request for encoder value
-Track an encoder value and brake the motor
-Set new baud rate for the driver

• Support up to 2A per phase
• Smoother stepper motor rotation with 2/5/10 micro-stepping feature
• Able to drive stepper motor from 3V to 40V.
• 8V to 24V compatible for driver circuit supply voltage
• 5V logic level compatible inputs.
• Maximum speed up to 1000 steps per second or 1KHz pulses
• Enable/Disable pin for low power consumption mode.
• Heat sink with fan for fast thermal release

Circuit diagram of motor driver and stepper motor