Internals of the miniSpinner
This is a photo of the motor and speed controller
used in the miniSpinner.
The motor is 23mm in diameter and 42 mm long. It's a
German-made coreless rotor 12 volt, 17 watt micromotor. The
shaft rides in two sealed high-precision ball bearings instead of
the bronze sleeves used on cheap motors. This motor is very quiet,
efficient, and has a remarkable
amount of torque for its size.
Motors like this are commonly used in aeronautical and spacecraft
applications like the Mars Rover, high-end medical robots and lab equipment, and that sort of
thing. They are outrageously expensive. If you wish to
buy one from the US distributor, it'll cost you $188 without the
sheave (whorl to you spinners). I make those on my Hardinge
The speed controller is 1.5 by 2 inches. This is the
almost-final prototype of my
latest design using mostly surface mount components, which means the
boards can be fabricated by automated machinery. I assemble
prototypes by hand, but the parts are tiny and it takes some
practice to solder them successfully. The smallest parts on
this board are 0.120 x 0.060 inches in size. I will go smaller
in the next model of miniSpinner as it'll have to fit much more
functionality in about the same amount of space.
I designed this speed controller. It controls
the motor speed using a technique called pulse width modulation (PWM),
which in simple terms means switching the power on and off very
rapidly at a specific rate and duration. It is a very
efficient way of controlling motor speed, and allows a motor to
produce close to its maximum torque at any speed.
This board contains a regulated 5 volt power supply for the PIC
microcontroller and associated circuitry, a self-resetting 1.2 amp
circuit breaker to protect against short circuits or overloads, and
a MOSFET that can handle loads of
up to 14 amps at around 55 volts for controlling the motor current.
Overkill, but highly reliable as a result.
The nice thing about using the microcontroller (the 8-pin
integrated circuit in the upper left corner of the board) is that it's programmable.
I can easily tailor the behavior of the speed controller by
reprogramming the chip. It also minimizes the number of
components which improves reliability.
I really like playing with this kind of stuff. Always have.