By: Anh Tram Do-Systems Engineer
The Hexapod will have power supplied from a portable source, such as a battery, so that it can be controlled remotely and without any other equipment.
The gait or walking pattern of the Hexapod must be chosen to maximize speed. However, the Hexapod should have an alternative stable walking pattern which can be used to operate in difficult or uneven terrain. We have concluded through our analysis of different gait patterns that the fasted gait is the tripod gait (link to Hexapod Gait Analysis). This gait alternates three legs at each cycle. The sturdiest gait is the wave gait. We will be incorporating both of this gaits into the final build.
A study was conducted to compare the different motor options for the Hexapod (link to servo and motor study). Servos proved to be the best option for the driving train of the build. The servos will be chosen to be within the $500.00 dollar budget project requirement outlined in the budget under our resource report blog (link to resource reports). They are to provide enough torque to lift the weight of the body as outlined in the body weight distribution report, also outlined under the resource report post, and allow for the Hexapod gaits to be executed.
To be able to navigate the terrain at the testing area (LINK) as well as to be able to fit inside the classroom for the final demonstration, the Hexapod is to be designed small enough to be easily carried. This means the Hexapod will be roughly the size of a large laptop, 17in x18in, or roughly 45cm x 45cm, and have enough clearance to walk over the terrain of the course. From Anh’s research of the terrain, the average terrain height is less than 5mm. The biggest obstacles encountered were 5cm tall, the Hexapod will be able to adjust its height and have an adequate size to account for these obstacles.
To control the Hexapod via first-person view interface system, the system will use a camera and sensors to collect on-board data. The system will use an accelerometer and gyroscope to measure and relay the orientation information of the Hexapod to user through a 3rd part application. To avoid using a specialized or sensor suite, we will be using an Android phone. The Android phone paired with the Arxterra Control Panel (link to Arxterra Control Panel) will allow for easy integration of a user interface.
The system will use the Arxterra Application in a mobile phone to control the Hexapod during its mission. Arxterra is a tele-robotics company developing open source which can control the robots from anywhere with cell phone coverage. The app allows the user to control the Hexapod through a user interface control panel. The Arxterra app will be installed on the Android phone and will fulfill the level 1 project requirement for telepresence (link to project requirement)
The Hexapod is a strong, durable and low cost robot. All components of the body will be made out of resin. A study has been conducted using solid works to test different potential materials, and we concluded that resin would be able to handle the weight of the robot of 16.7 (link to weight report) Newtons without bending or cracking (link to materials study).
The battery chosen for the build will need to provide power for 18 servos and the control board. It will need to be rechargeable and be within budget. The weight of the battery must not excess 1/5 the weight of the full Hexapod. The battery must have better run time to provide full electricity for at least 20 minute operation. It must also provide enough current for all servos. The suitable range of current is from 2700mA to 3600mA (150mAh to 200mAh per servo). The battery should have a high discharge rate order to deliver the large amount of power at once. For safety requirement, the maximum safe continuous discharge rate must be greater than the maximum current drawn from the servos and electronics boards (link to study on battery options)