Force Mode

In this tutorial we will demonstrate use of the force control mode of ORCA motors.

Prerequisites

• Modes of Operation

• Motor Error Handling

• Command Stream

---

We’ll start with the following code, which is a modified example from the command stream tutorial displaying force instead of position. We recommend using command streaming when controlling the motor via force mode.

C++

#include <iostream>
#include "actuator.h"

using namespace orcaSDK;

int main() {
	Actuator motor;

	int serial_port;
	std::cout << "Please input the serial port number of your connected motor. ";
	std::cin >> serial_port;

	motor.open_serial_port(serial_port);

	motor.enable_stream();

	while (true) {
		motor.run();

		std::cout << "Current Force: " << motor.stream_cache.force << "             \r";
	}

	return 0;
}

Python

from pyorcasdk import Actuator

motor = Actuator()

serial_port = int(input("Please input the serial port number of your connected motor. "))

motor.open_serial_port(serial_port)

motor.enable_stream()

while True:
    motor.run()

    print("Current Force: " + str(motor.get_stream_data().force), end="        \r")

Command a Force

To begin, let’s set the motor into force mode.

C++

...
motor.enable_stream();

motor.set_mode(MotorMode::ForceMode);
...

Python

from pyorcasdk import MotorMode
...
motor.enable_stream()

motor.set_mode(MotorMode.ForceMode)
...

At this point the motor is ready to receive force commands. Let’s give it one.

C++

...
motor.enable_stream();

motor.set_mode(MotorMode::ForceMode);

motor.set_streamed_force_mN(10000);
...

Python

...
motor.enable_stream()

motor.set_mode(MotorMode.ForceMode)

motor.set_streamed_force_mN(10000)
...

Try running the program, you should notice that the shaft moves. Try opening IrisControls. It should display that you are in force mode, and that it’s detecting a force of around 10 newtons.

Timeout Error

Now close your program and run it again. This time you may notice that the shaft does not move. Take a look again at IrisControls. It should be displaying that an error has occurred, particularly a “comms timeout”. Some ORCA modes, including force mode, require that regular communication happens with the motor, else it will stop exerting force. This is a safety feature. When actively giving a motor commands, any stops in communication are interpreted as a failure or shutdown of the system at large.

In order to resolve this issue, lets clear errors before beginning. This will allow the program to run again.

C++

...
motor.set_mode(MotorMode::SleepMode);

motor.set_mode(MotorMode::ForceMode);
...

Python

...
motor.set_mode(MotorMode.SleepMode)

motor.set_mode(MotorMode.ForceMode)
...

After adding this command in, your program should run as normal again.

---

Complete Example

C++

#include <iostream>
#include "actuator.h"

using namespace orcaSDK;

int main() {
	Actuator motor;

	int serial_port;
	std::cout << "Please input the serial port number of your connected motor. ";
	std::cin >> serial_port;

	motor.open_serial_port(serial_port);

	motor.enable_stream();

	motor.set_mode(MotorMode::SleepMode); // ORCA motors raise an error when communication stops during force mode

	motor.set_mode(MotorMode::ForceMode);
	
	motor.set_streamed_force_mN(10000);

	while (true) {
		motor.run();

		std::cout << "Current Force: " << motor.stream_cache.force << "             \r";
	}

	return 0;
}

Python

from pyorcasdk import Actuator, MotorMode

motor = Actuator()

serial_port = int(input("Please input the serial port number of your connected motor. "))

motor.open_serial_port(serial_port)

motor.enable_stream()

motor.set_mode(MotorMode.SleepMode)

motor.set_mode(MotorMode.ForceMode)

motor.set_streamed_force_mN(10000)

while True:
    motor.run()

    print("Current Force: " + str(motor.get_stream_data().force), end="        \r")