Unipolar Stepper Motor Controls

	Unipolar Stepper Motor Controls (6 wires)
Homepage Astronomy Equatorial Table Hydraulic Focussing Stepper Motor How To Make A Telescope Information for Beginners Links And Bibliography Gastronomy Recipe Schematics Recipes To Bake A Well-Risen Cake Links Photography Astronomy Architecture Animals Landscape Crafts Livroscope Read Html Books On Screen High Rise Handlebars Bike Dominoes Power Electronics Heatsink Impedance Chess http://queribus.free.fr	Stepper motors have performances adapted to the requirements of astronomy. DC and synchronous motors are now to be avoided. 1. Advantages of Stepper Motors 1.1 Constant Speed Unlike DC motors which slow down when torque increases, stepper motors turn one step for each oscillation of the clock that pilots the electronic controls. Speed is independant from torque. 1.2 Electronic Controls Are More Simple DC and synchronous motors can turn without electronic controls whereas stepper motors cannot. However to obtain a constant speed, electronic controls are more complicated for DC and synchronous motors than for stepper motors. 1.3 Low Rotation Speed Stepper motors can stay still with a torque on their axle and move only one step when the clock sends the signal. This allows them to turn very slowly with full control on speed, which is not possible with DC and synchronous motors. 2. Motor 2.1 Characteristics Your motor may differ from the one described here. A few components will need different values. Here are the characteristics of the motor I used: Voltage: 5,1 V Windings' resistance: 5 ohms 200 steps/rev	Table des matières 1. Advantages of Stepper Motors 1.1 Constant Speed 1.2 Electronic Controls Are More Simple 1.3 Low Rotation Speed 2. Motor 2.1 Characteristics 2.2 Wiring of The Motor 3. Electronic Circuit 3.1 Power Circuit 3.2 Control Circuit 4. Power Supply
	2.2 Wiring of The Motor If the 6 wires of the unipolar stepper motor are not labeled, you just need to measure the resistance between all wires to find out how coils are connected. In this example: 5 ohms between 1 and 2, 10 ohms between 1 et 3, infinite resistance between 1 and 4.	Wiring of a unipolar stepper motor
	3. Electronic Circuit The circuits described hereafter require a stabilized 5 V DC supply. The complete control circuit of the motor is made of 3 units: The power circuit with transistors that switch the energy supplied to the motor The control circuit that commands the transistors at the right time. The clock that determines the speed of the motor
	3.1 Power Circuit The power circuit supplying energy to the stepper motor Transistors are controlled by A, B, C and D connections described in next scheme. The motor is connected to wires labelled 1 to 6.
	3.2 Control Circuit a. SGS-Thomson's L297 Controller L297 is specialized in stepper motor control. It triggers the transistors at the right time to set the speed determined by the clock. Wiring diagram of a L297 in DIP 20 package.
	b. NE 555 oscillator This classical component which has multiple applications is here used to set the speed of the motor. For each pulse, the motor turns one step. The frequency is given by the formula: With those values, the rotation speed varies between 0.6 steps/s and 595 steps/s, that is between 0.18 rev/min and 178 rev/min. Practically, the quality of pulses and the characteristics of the motor do not let you to reach these limits. 4. Power Supply This motor must be able to turn in damp locations. I chose a sealed lead-acid battery, 6 V, 10 Ah. Ni-Cd and Ni-MH batteries are better but more expensive.	Oscillator using NE 555