speed does not depend on
the torque applied on the axis
controls are more simple
great speed range available
The characteristics of stepper motors make them quite suitable for astronomical use. Continuous current and synchronous motors are now to be replaced by stepper motors.
speed does not depend on
the torque applied on the axis
controls are more simple
great speed range available
Voltage: 5.1 V, coil resistance: 5 ohms, 200 steps/rev
Electronic circuits hereafter described work with a stabilised continuous
5V voltage.
The complete controls of the stepper motor consist in 3 parts:
the power circuit where transistors
manage the energy supply of the motor
the controller that controls
transistors
the oscillator that gives
the speed of the motor
Just mesure the resistance between each wire to determine the coil wiring.
It provides energy to the coils of the motor. Transistors are driven by the L297 controller described on the following plan. Zener diods' are to protect the controller is case of an ill wiring of the motor that could blow up the transistors.
The L297 controller from SGS-Thomson
The aim of this component is to switch the transistors at the right time so that the motor can turn at the speed wanted by the user.
The NE555 oscillator
This classical multiple application component is here used to give the
speed of the motor. For each oscillation the motor goes 1 step ahead. The
frequency is given by the formula:
f = 1,44/[(R1+2.R2).C1]
R1 = 2,2 Mohm, R2 = 1,1 kohm, C1 = 1,1 µF, C2 = 22 nF
With the components I chose, the rotation speed goes from 0.6 step/s to 595 steps/s, that is to say from 0.18 rpm to 178 rpm. Practicaly, the quality of the oscillations and the motor high speed characteristics do not enable the motor to reach these limits.
The energy supply
This motor is to turn in a humid atmosphere. I chose a 6 V, 10 Ah waterproof lead battery (cheapper ones). Ni-Cd or Ni-MH have far better characteristics but the price is much higher. It is difficult to know the use of the equipment before buying it, even more difficult when you often change your experiments. Do not forget to buy a suitable battery charger. Some batteries could be greatly damaged if charged with the wrong charger.