Milestone 3

Implementation

Fig. 1. Control signal for ESC controller.

Fig. 2. ESC wire connector.

Fig. 3. PixHawk motor outputs.

To control the motors, the Electronic Speed Controllers (ESCs) require a PWM signal at 50 Hz with a duty cycle between 5% and 10%. The PixHawk 2.4.8 being used has a dedicated output to control the motor at the top. It is able to provide the PWM signal, +5V, and ground required to control the ESC.

Fig. 4. Rocket 3660 3250KV Motor and 

90A Brushless ESC.

Fig. 5. SIPYTOPF Servo Motors.

The team is using three Rocket 3660 3250kV Motors to propel the boat through a water jet system. These are Brushless DC Motors (BLDC) that operate at a maximum of 60,000 RPM at 14V and a continuous current of 90A. 

For the ESCs, the team has chosen to use the 90A Brushless ESC. These motor controllers require cooling based on the high current being passed through. A pump is used to pass water through the ESC for cooling.

For steering, the team has chosen SIPYTOPF servo motors. These motors are controlled by the PixHawk directly and offer precise control of the angular position.

Fig. 6. Implementation of the system.

The photo shown above shows the implementation of the system with all components connected. The PixHawk is used as the main controller and is able to provide autonomous navigation from ArduPilot. In addition, the power is supplied by six Liperior 16000mAh Lipo Batteries, which are connected to the positive and negative terminal bus bars.

Testing

PixHawk Motor Test.mp4

Fig. 7. Test of motors with PixHawk.

The video shown above (Fig. 7) is a demonstration of the PixHawk controlling the motors. The ESC steps up the RPM from the start to 30% throttle. In addition, the PixHawk is able to steer the rudders using the servo motors based on the duration of the input signal given to the servo motors.

Fig. 8. Sealed ports of the water jets.

Fig. 9. Boat with weights in the tow tank.

At the previous year's competition, the team reported that the water jets had a significant amount of leaks. The previous silicone sealant was removed and replaced with a putty seal to address this issue. Testing the putty seal showed an improvement. However, leaks continued to flood the boat. 

A second test was conducted to see if the back panel was leaking. Electrical tape and acrylic sheets were used to seal the ports of the water jets (Fig. 8). After placing the boat in the tow tank (Fig. 9), 10 kg of weights were placed in the boat to simulate the boat with all the batteries and subsystems on it. 

Fig. 10. Leak at the water jet.

The leak test showed that the back panel and water jets were leaking significantly. A new solution was proposed to build a new end for the boat with proper seals. 

In addition to a leak test, a thrust force measurement test was conducted. The center motor was jammed from rust, leaving the boat with two operational motors. Using the RC backup system, the boat was shown to produce 10 lbs of force at 60% throttle with two operational motors. The boat was not operated at 100% throttle due to the possibility of a collision with equipment in the tow tank. However, the boat was estimated to produce 14 lbs of thrust force at 100% throttle with the two operational motors. 

Teamwork

In terms of teamwork, each group member contributed equally to implementing and testing the system. Teams were given tasks to complete on either the hardware side or the software side. Splitting the task into two teams allowed for faster implementation of the system and allowed the team to be able to work through problems easily. An example is the PixHawk not pairing with the ESCs. This problem was evaluated by both the hardware team, that measured input and output voltages to determine whether the system was functioning correctly, and the software team, who searched the documentation of ArduPilot and changed the state of variables in the software to enable the system to work.