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AN #112 - Speed controller for modelboats
Speed controller for model boats
This AN is submitted byAlonzo Trueland.
Download source codeRC SPEED CONTROLLER
BASIC DESCRIPTION
This application note describes a circuit designed to control
the speed of a dc motor used in radio-controlled boats.
Theelectronic speed controller (ESC) is a no-brake, forward-only
controller.I wanted to keep the part count low and the circuit
simple so a couple features were sacrificed. The circuit does
not have: over-current protection, over-temp protection,
polarity
protection, or over/under voltage protection. All the parts can
be obtained from digikey distributors. The circuit was designed
with a popular 12-cell model boat motor in mind (graupner speed
700). This project was my first attempt at using Bascom-avr
and Atmel microcontrollers.
CIRCUIT DESCRIPTION
The ESC is designed around an Atmel AT90S2313 microcontroller. I
chose to build the circuit on two separate boards, a digital
control board, and a FET driver board. The digital control
section is powered by 4.8-6Vdc from the receiver and the FET
driver
section is powered by 12 NiCad cells (14.4Vdc).
The ESC receives the 1-2mS pulses from the receiver and converts
it into a 2400Hz PWM signal that drives the FET board
controlling the motor. The AT90S2313 converts the receiver
signal into the motor drive signal then feeds it into an opto-
isolator. The isolator converts the logic level signal into the
14.4Vdc signal needed for FET operation. The signal is then fed
into a 9A FET driver chip. The FET driver is responsible for
providing the short high current pulses needed to overcome gate
capacitance. Three LEDS and a button are used for
calibrating/arming the controller.
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SOFTWARE DESCRIPTION
The software begins by calculating the center and full forward
values. A button is pushed when the transmitter stick is at
center and once again when the stick is full forward. These
values are stored as Dbf and C. After storing the center and
forward values, the software waits for the stick to return to
center before arming the circuit. The armed led will come on
afterthe stick is returned to center. Next a continuous loop of
measuring the RX signal and updating the PWM drive signal is
performed. IF two consecutive pulses are missed, the mispulse
routine will turn off the motor drive.
OPERATION
1.Connect receiver to the ESC receiver connections.2. Connect
motor to the ESC motor connections.3. Connect battery to the ESC
battery connections.
4.Turn on receiver switch. Two ESC LEDs should be on.
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5. Turn on transmitter.
6. Press the calibrate button once with the transmitter in a
neutral position. Center LED should go out.
7.Press the calibrate button once again with the transmitter in
a full-forward position. The forward LED should go out.8.Return
transmitter to a neutral position. The Armed LED should go on. The
speed controller is ready.
FINAL NOTES
I chose to build the circuit using point-to-point because of the
relatively low parts count and large wires needed for
current handling. The thick traces on the schematic represent
where 12 gage wire should be used. Circuit layout andpackaging is
left to the builder. I chose to use IRF540s for convenience and
price. The number and quality of FETs can be
changed to meet the demands of the builder, but must be N-type
and rated for 100Vdc. The use of a heat sink is
recommended. In model boats it is common to water-cool the FETs.
The number, quality, and cooling efficiency of the
FETs will determine current capability. Because this circuit
does not include some safety features that you would f ind on a
commercial unit, the builder/operator should exercise caution
when experimenting with this device.
DISCLAIMER
This information is for experimental use only. I do not assume
any responsibility for injury or damages resulting from the use
of any information found in this application note.[ Back ]
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