Final Demo

Check out our demo!

Final Report

For a more detailed look at the hardware and software we used to make the pivot board check out our final report here!

Pivot Board!

Steering Control

Since steering is really difficult do by just waving your arms around, we developed a glove-based steering controller shown below.

The steering controller consists of two parts the glove itself and the yellow case which the user straps on. There are two pressure sensors, outlined in red thread, sown into the glove. The user can press the left pressure sensor to send a "turn left" signal to the board and the right sensor to "turn right." The harder the user presses on the pressure sensor the faster the board will turn in that direction. The leads of the pressure pads are wired to the mbed in the yellow casing. The mbed sends the pressure-based analog turning command to the mbed on the pivot board every few milliseconds via the red wireless module also housed in the yellow casing. There is also emergency brake switch on the right side of the yellow housing unit. If the switch is pressed, the mbed will signal the mbed on the board to immediately brake, freezing the motor.

Here is Justin testing out steering control :

You can also ride the pivot board segway style!

Initial Testing

The board runs! Fairly well... Initialization is a tough at the beginning, but once you stabilize riding the board is pretty intuitive. Here's our first test run, there is no way to control steering at this point. That will be our next step.

Controlling Both Wheels on the Board

We can control both motors! Here there are two control loops running, one to increase the PWM duty cycle of both motors in response to vertical tilt of the IMU. The other control loop handles turning correction so if the IMU is tilted horizontally, the PWM duty cycle of one motor will be decreased to keep the pivot board on a straight path.

The video below shows basic control of both wheels based on the tilt angle of the IMU. As shown in the video, when the breadboard, which the IMU is on, is flat, the wheels stay relatively still. When the board is tilted in one direction, both wheels turn rapidly in the same directions. The board can also be quickly shifted in either direction and the wheels respond accordingly. When the breadboard is turned, one wheel slows down and the other speeds up which demonstrates correct to turning correction functionality.

Board Fabrication

The next step is fabricating the actual pivot board. Since the mounting holes of the rear wheel power train of the scooter has two levels, one set above the wheel and the other above the motor, the board also needs to have dual levels. Our initial deign is shown in the SolidWorks model below.

We cut a large plank of plywood into one square with center cutouts for the wheels, a center support piece with wheels cutouts and a solid center support strip to cover the wheels. The two central pieces were mounted to the main square board using  12 30mm bolts spaced over the center strip.

Originally we planned to mount the 12V Lead Acid battery to the top of the board but for weight-balance reasons and fear of tripping over the batteries choose to mount the batteries to the bottom of the board. Cardboard wrapped steel cables were used to mount the batteries to the bottom of the board and 2 inch nails were used to keep the batteries from sliding around. The motor controllers were also mounted to the bottom of the board using mounting tape and lots of gaffers tape. Below is a picture of the mounting arrangement on the bottom of the board.

The rear wheel power trains from the scooters are outlined in orange, the batteries are outlined in green, and the motor controllers are outlined in red. Lots of tape was used to secure the controllers and loose wires from the batteries and motors.

To keep the rider from tilting too far over and rubbing the edge of the lead acid batteries across the ground, we nailed in three layer slabs of plywood to each end of the board. A thin layer of packing foam was also tapped to the top of each wooden "tooth" to pad the tops of the wooden teeth.

Motor Driver Board

Because the E90 Razar Scooter can with a single direction motor controller, we are using MD07a motor drivers to interface with the motors. The driver circuit should below is connects to the 12V lead-acid battery and the outputs the two leads of the motor based on the two logical PWM and direction input. Since the mbed's logic 1 is 3.3V and the driver's minimum voltage from a logic 1 is 3.5V, we are using a comparator chip to boast the mbed's logic 1 output to 5V for both the PWM signal and the direction signal.

Here is a video of the motor driver board being used to interface with the rear wheel assembly of the E90 scooter and run the motor up to full speed.