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Futaba servo signal interface
D Motor connection
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Illustrated Is the connection diagram for a motor that is to be controlled forwards and backwards by two relay drivers.
This is a simple wiring procedure to control a motors direction. Two relays are needed per motor; they must have changeover contacts for this to work. The coil voltages must be between 12v and 24v. The reason for this is the limiting factor of the LM7805 Voltage regulator as it can only have an initial voltage of 35v on its input. If a higher voltage relay is desired, a compatible 5v, voltage regulator with a higher maximum input voltage can be substituted. The LM7805 does not regulate the relay coil voltage but because the coil voltage is run from the same supply as the logic the Voltage regulator becomes the limiting factor. The relay coil current should not exceed 600-700ma of operating current.
Each of the changeover contacts are connected to the motors supply contacts as seen above. The two normally closed contacts are attached to either the positive or negative rail of the motors supply voltage. The normally open contacts are connected to the opposite. The polarity does not matter.
The coils of the relays should be attached to a length of wire that has a 2 pin IDC female plug on the end. This will plug directly into one of the 2 pin ICD connectors from the output of the relay driver (JP5 - JP12, see Appendix B). The relay coils must be plugged into the corresponding driver that is controlled by the pins being used in your program. (See Appendix B for jumper - port B pin matching).
The circuit works simply by driving one relay at a time to activate the motor. Activating one relay will turn the motor in one direction, activating the other will turn it in the opposite direction. If both are in the same state there will be no motor movement as both sides of the motor will be seeing the save voltage. Because of this an interesting effect is created. The motor when in its off state will not spin freely because when a motor is turned by hand a current is generated in the coil winding. Because both sides of the motor are connected together in it's off state this current passes around through the winding and causes an opposing force. This creates a kind of electrical brake which helps hold motors in one position after being turned off and also helps them stop more abruptly instead of coasting to a stop.
If you test the program with your wiring setup and you find that the motor isn't spinning in the direction you want it to, simply switch the plugs for P1 and P2 around. This will reverse which relay is activated when the control is pressed and in turn will reverse the direction of the motor.
NOTE: If the induced voltage on the relay coil cause the microcontroller to brown out during turning the coils on and off place a 0.1uF - 1uF capacitor across the coil terminals.
This will absorb spikes in the voltage during coils switching which may cause the microcontroller to reset itself, causing error and stuttering in its operation. While the 3300uF capacitor on the 5v logic supply will stop brownouts during switching it may not be up to the task of absorbing small voltage spikes during the deactivation of the coil.
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Futaba servo signal interface
D Motor connectionFutaba servo signal interface
Appendix
D Motor connection
Illustrated Is the connection diagram for a motor that is to be controlled forwards and backwards by two relay drivers.
This is a simple wiring procedure to control a motors direction. Two relays are needed per motor; they must have changeover contacts for this to work. The coil voltages must be between 12v and 24v. The reason for this is the limiting factor of the LM7805 Voltage regulator as it can only have an initial voltage of 35v on its input. If a higher voltage relay is desired, a compatible 5v, voltage regulator with a higher maximum input voltage can be substituted. The LM7805 does not regulate the relay coil voltage but because the coil voltage is run from the same supply as the logic the Voltage regulator becomes the limiting factor. The relay coil current should not exceed 600-700ma of operating current.
Each of the changeover contacts are connected to the motors supply contacts as seen above. The two normally closed contacts are attached to either the positive or negative rail of the motors supply voltage. The normally open contacts are connected to the opposite. The polarity does not matter.
The coils of the relays should be attached to a length of wire that has a 2 pin IDC female plug on the end. This will plug directly into one of the 2 pin ICD connectors from the output of the relay driver (JP5 - JP12, see Appendix B). The relay coils must be plugged into the corresponding driver that is controlled by the pins being used in your program. (See Appendix B for jumper - port B pin matching).
The circuit works simply by driving one relay at a time to activate the motor. Activating one relay will turn the motor in one direction, activating the other will turn it in the opposite direction. If both are in the same state there will be no motor movement as both sides of the motor will be seeing the save voltage. Because of this an interesting effect is created. The motor when in its off state will not spin freely because when a motor is turned by hand a current is generated in the coil winding. Because both sides of the motor are connected together in it's off state this current passes around through the winding and causes an opposing force. This creates a kind of electrical brake which helps hold motors in one position after being turned off and also helps them stop more abruptly instead of coasting to a stop.
If you test the program with your wiring setup and you find that the motor isn't spinning in the direction you want it to, simply switch the plugs for P1 and P2 around. This will reverse which relay is activated when the control is pressed and in turn will reverse the direction of the motor.
NOTE: If the induced voltage on the relay coil cause the microcontroller to brown out during turning the coils on and off place a 0.1uF - 1uF capacitor across the coil terminals.
This will absorb spikes in the voltage during coils switching which may cause the microcontroller to reset itself, causing error and stuttering in its operation. While the 3300uF capacitor on the 5v logic supply will stop brownouts during switching it may not be up to the task of absorbing small voltage spikes during the deactivation of the coil.
