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Control a small DC motor with the same signal used to control a hobby servo.

RCDC

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Intro:


The RCDC board is a motor controller for small DC motors that works with the same pulse signals that are used to control a standard hobby servo.


It can be operated with most anything that can be used to control a standard hobby servo;


  1. 1.Radio Control receiver

  2. 2.Arduino using the Servo Library (or other micro controller)

  3. 3.Pololu Micro Serial Servo Controller

  4. 4.etc ...

How it works:


The RCDC came about through experimenting that was done to create the motor drive circuit for the Mobile Platform.


The RCDC works the same way as the circuit in the initial version of the Mobile Platform, when the servo pulse is in the middle position (90 degrees) there is no motor motion. As the “control stick” is moved the motor will gradually turn faster either clockwise or counter clockwise depending on how far the servo signal is from either extreme.

Specifications:


  1. 1.Power LED

  2. 2.RC signal OK - LED

  3. 3.Auto-motor shut down if RC signal is lost

  4. 4.Main power input from 5 to 13.5 volts

  5. 5.Drives standard DC motor up to 2 amps

  6. 6.On board PCB copper heat sink

  7. 7.Auto power drop (brown out) reset

  8. 8.On board logic voltage regulator

  9. 9.Uses averaging algorithm to smooth “choppy” RC signal

  10. 10. Two power source options, power from RC device or from dedicated motor supply

  11. 11. BBC - Bread board compatible

Usage:


The first step in setting up your RCDC board is deciding how you are going to power your project.


There are two ways to power your RCDC board and motor.


  1. 1.Power everything from one battery or power supply. Use this option if your DC motor is low current and it’s voltage is compatible with your RC receiver’s voltage, usually around 6 volts. (If you are using an Arduino to create the serial signal, it is not recommended that you power the DC motor from the Arduino board.)

  2. 2.Separate power for RC device and motor board. Use this option if you are using a higher current motor or one who’s voltage is higher then the RC circuit, for example a 12 volt motor.

Build the kit:

Wire up your RCDC board as illustrated above.


Important: Even if you are using a separate power supply for the RCDC board and motor, there must be a common ground connection between the RCDC board and the source of the RC pulse signal. The “B” on the connector on the upper left side of the RCDC is for the “Black” ie ground wire that connects to your receiver (or ground on your Arduino).

You can assemble the RCDC kit in a different sequence then the one presented here, but we find these steps make it the easiest.


Also, there are some optional build steps, so plan on how you will use the RCDC board before soldering those parts.

Step 1:


Start with the resistors:


First using only your fingers bend the leads at a 90 degree angle to the body of the resistors.


Next, place the resistors into the PCB in the places marked R1 to R5.


After the resistors are soldered in place, inspect the solder joints then trim the leads to be nearly flush with the PCB.

Step 2:


Solder the 8 pin socket, onto the spot marked “U1”. You may need to tape it in place to hold it in while you flip the board over.


Note:

  1. 1.The side with the curve / notch goes toward the left, like the silk screen. The curve indicates the orientation of the chip that goes into the socket.

2. There is no socket for U2.

Step 3:


Soldering the 16 pin dip onto the PCB. This is the hardest step! This chip goes directly onto the PCB without a socket. No socket is used here, since the PCB is used as a heatsink. The four center pins are designed to dissipate heat and are connected to a large copper area on the PCB. This makes it hard to solder due to the cooling effect that it has on the soldering iron’s tip. If you have solder flux, it is recommended that you use it on the four center pins.


NOTE:

The small dimple on the top of the chip goes toward the left.

Step 4:


The voltage regulator is the three legged TO-92 part. You may have to bend the center leg backward a little to get it to fit into the spot marked VR1. It is best to leave the body of the voltage regulator around 1/4” above the PCB.

Step 5:


There are five small blue capacitors that go into spots marked C1 to C5. The capacitors can go in either direction and are all the same value.


C6 is polarized, meaning it only goes in one way. Match the “-” on the capacitor with the “-” on the PCB, slid it in all the way and solder it.

RC Servo pulse compared to standard servo position and motor speed.

Full speed CCW

Stopped

Full speed CW

RCDC pinout with typical servo wire color code.

NOTE: There are two values of resistors used on the RCDC board; 1k ohm and 10k ohm. The color codes are similar; 1k Brown-Black-Red and 10K Brown-Black-Orange.


Be careful, the red and orange some times look similar!

Step 7: Last step !


Depending on how you are going to use the RCDC board this last step has options.


  1. 1.The RCDC kit includes male pin headers and a jumper. If you want to plug the RCDC into a bread board then solder these parts onto the bottom. (It may be easier to keep them straight if you first push them into a breadboard then lay the RCDC PCB onto them for soldering.)

  2. 2.The male pins may also be soldered pointing up for use with patch cables.

  3. 3.You can also skip the pin headers altogether if you are going to solder wires directly to the RCDC.

Step 6:


The kit comes with two LEDs. They must be installed into the PCB with their long leg going into the hole marked “+”.


The color choice is yours. The LED marked “PWR” will be on all the time while the board is powered. The LED marked “RC” will only be on while the RCDC is receiving a valid RC signal.

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