Encoder Detail

A key part to the robot's mobility system are the encoders mounted on each drive wheel. An encoder is a device that measures rotation by converting angular position into digital or analog code. This lets the control system of the robot control the precise angular position of whatever rotating body the encoder is being used on. In the case of the robot each powered drive wheel has an encoder attached to it's drive shaft. This let's us control the exact angular position of the drive wheel. This can be thus used to control the exact speed or position of the wheel.

Mobility system cutaway

Here is a cutaway of the robot's mobility system. Here we can see the two motors powering the tread module on the left (as well as one of the motors powering the right-side module). The gearboxes are of a two stage design, meaning that there are two gear reductions in between the input and output shafts. Also note the encoder (the black cylinder with two pegs sticking out) on the side of the rightmost module. This device accurately measures the RPM of a spinning shaft, allowing the robot to move and turn very precisely. 

Aesthetic redesign

I have decided to change the design of the robot's body for mostly aesthetic reasons. The new body design is sleeker and now fits the profile of the tread. The new body is also symmetric on both the x and y axis which makes it simpler to work with in the computer.

1st iteration of the main body frame and sensor turret

I have completed two components of the robot this week. The first is the outside shell of the robot's main body. This part, shown above in between the two treads, serves to house the robots electronics as well as the motors that power the treads. The second part is the sensor turret (pictured on top of the robot) that will contain the robot's optical sensors. Both parts right now are just empty frames, I plan to add all of the electronics these components house in the future.

Complete tread module assembly

Here is the 3D model of the complete tread module assembly. There will be one of each on each side of the robot. The module consists of a 6 inch diameter drive wheel in the center that is driven by a motor through a gearbox. The drive wheel drives the rubber tread that wraps around the module. On the bottom of the module are 8 idlers (unpowered wheels) that act as the robot's suspension system. This system is designed to allow the robot to efficiently maneuver through rough terrain and drive over small obstacles.

Drive and Suspension 2D Drawings

The first part of the robot that I am designing is the drive modules. There will be one module on each side of the robot. Each module contains a 9 inch powered drive wheel and two suspension bogeys each containing a 6 inch and a 5 inch idler. The two drawings above are 2D side views of the module that I made in order to calculate the correct dimensions and angles.

My Robot

For my 20% project I have decided to design a robot. I have christened it SABER, or Semi-Autonomous Bio-mechanically Engineered Robot. My idea is do design a robot with a humanoid torso yet a tracked mobility system. Tracks, or "Tank Treads", were chosen over a humanoid bipedal like system due to the simpler nature of the former and the technological complications of the later. The torso however will be designed to mimic the bio-mechanical movements of a human torso and arms, hence the "bio-mechanically engineered" in the name. I will design the robot using Solidworks, a professional 3D design software I have used for robotics and NASA work in the past. Every week I intend to post parts of the robot I have designed or conceptualized, culminating with a complete robot design that I will unveil near the end of the school year. Stay tuned.

- A. Hallberg