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The motor port on the Cricket is designed around the Lego motor. However,
these motors are expensive and limited in motion, power, and size. This
document explains how to use any motor you find with the Cricket system.
Motors of all types can usually be found very cheaply at www.mpj.com or
www.goldmine-elec.com. There are many different types of motors- DC, AC,
servo, and stepper. All of these types can be driven (almost!) with the
Cricket. DC and AC motors can be hard to tell apart- it should be printed
somewhere on the motor and give its voltage rating. Servo motors and stepper
motors both have three wires- a stepper motor will feel like it is 'stepping'
as you turn the shaft; a servo probably won't turn. Once you have seen
a few of each of these types, you will be able to recognize them. We will
go through all cases below.
DC: We have many options here. Look at the motor specs- they might
be printed on the motor or should be given when you buy a motor. From
here, we will differentiate between two different types of motors based on
one of two criteria: either bigger (physically) than a gray Lego motor
or rated greater than 9 Volts (like big fans, big pumps, etc), and those
otherwise (pager motors, small pumps, little hobbyist motors).
Bigger than gray Lego motor or greater than 9 Volts: For these
motors, use the Relay bus device or the Big Motor Driver bus device. The
Relay bus device can switch directions, but cannot control the motor's
speed. The Big Motor bus device can control the motor's speed and direction.
Contact Casey (csmith@media.mit.edu)
if you would like one of these devices.
Otherwise: This process involves soldering a resistor onto one
of the leads of the motor. A photo of this can be found here.
First, however, we need to calculate the value of the resistor needed.
Here is a calculator for determining these values.
For those of you that want to do this by hand, click here.
AC: These motors call for the Relay Bus device.
Servo: For these, you will need a Servo bus device.
Stepper: While do not yet have a stepper motor bus device, it
probably will be coming soon. If there is a specific project that needs
a stepper motor, please write to Casey (csmith@media.mit.edu).
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