A half hour meeting with my supervisor Ben Hicks lead to several ideas worth noting.
First of all the creation of this blog as an easy method of documenting my progress and design decisions during the build phase.
Secondly was the idea of some sort of test rig to prove that the control system works with out the need for a brave volunteer to stand on board!
It was invisaged this would be in two parts, a desk mounted RP'd 'joy stick' with the MPU mounted to simulate the input into the system. A rig to hold the motors and wheels would then also be built. As the motors are operating in locked antiphase it seems logical that accurate control should be acheivable with no load. However it might also be sensible to add a resitive load to simulate motion via a belt or chain drive. The angular velocity of the motors could be measured by means a of a simple encoder making use of the spokes of the wheels (ir led and receiver, interfaced via arduino).
This could all be put back through the numerical model of the device to check the stability before practical testing comences.
Friday, 27 February 2015
Progress to date
I am starting this blog to keep track of my 3rd year Individual Research Project for Mechanical Engineering at the University of Bristol.
The project is about the design and optmisation of a 2 wheeled self balancing vehicle (Segway) as a mobility aid for children with mobility issues.
It aims to provide a cheap, portable and unobtrusive way for children who can stand easily but find movement difficult.
The advantages of this proposal over a traditional mobility scooter or powered chair lies in its ability to have a very small foot print, allowing greater moveability inside buildings and out, whilst also having less of a visual impact which can provide a certain stigma.
Current design decisions have been based on pre existing projects such as the "Open Wheels Project." The motors, batteries and mechanical components have been purchased / built in line with the descriptions in those documents.
The control system has been decided to be run of an Arduino Due micro-controller board. This provides a multitude of both Digital and Analogue (PWM) I/O pins. It is also has a suitably fast clock speed to be able to analysise data from the Gyro and Accelerometter at a suitable rate.
The Gyro and Accelerometer used is a single 6 DoF package: MPU 6050, supplied packaged on a break out board from spark fun. This will interface with the Arduino via the I2C bus, and this data will then be processed through a digital control system to send output to the motors.
The motor drivers chosen have been the polulu 24v12 . One of these will control each motor. These drivers were chosen as a cost effective method of driving the motors, with out the need for designing and building our own PCBs. It was also essential to find a driver that would opperate a H bridge driver in locked antiphase mode, to provide the precision actuation of the wheels, and the internal braking required for this project to run succesfully.
The photo above shows the current configuration of the control board with the Arduino conected to the MPU via crimped jumper leads ( for easy redesign and reliable connections). Also connected is a thermister opperating as a potential divider which is intended to be used to measure the opperating temperature of the motor drivers to ensure that this is not at a dangerous level.
Alongside the practical design and build section of this project, numerical analysis in the form of a computer simulation based on a modified inverted pendulum will also be carried out. This is currently been done using GNU Octave, and Open Source alternative for Matlab which runs well on Linux.
The project is about the design and optmisation of a 2 wheeled self balancing vehicle (Segway) as a mobility aid for children with mobility issues.
It aims to provide a cheap, portable and unobtrusive way for children who can stand easily but find movement difficult.
The advantages of this proposal over a traditional mobility scooter or powered chair lies in its ability to have a very small foot print, allowing greater moveability inside buildings and out, whilst also having less of a visual impact which can provide a certain stigma.
The control system has been decided to be run of an Arduino Due micro-controller board. This provides a multitude of both Digital and Analogue (PWM) I/O pins. It is also has a suitably fast clock speed to be able to analysise data from the Gyro and Accelerometter at a suitable rate.
The Gyro and Accelerometer used is a single 6 DoF package: MPU 6050, supplied packaged on a break out board from spark fun. This will interface with the Arduino via the I2C bus, and this data will then be processed through a digital control system to send output to the motors.
The motor drivers chosen have been the polulu 24v12 . One of these will control each motor. These drivers were chosen as a cost effective method of driving the motors, with out the need for designing and building our own PCBs. It was also essential to find a driver that would opperate a H bridge driver in locked antiphase mode, to provide the precision actuation of the wheels, and the internal braking required for this project to run succesfully.
The photo above shows the current configuration of the control board with the Arduino conected to the MPU via crimped jumper leads ( for easy redesign and reliable connections). Also connected is a thermister opperating as a potential divider which is intended to be used to measure the opperating temperature of the motor drivers to ensure that this is not at a dangerous level.
Alongside the practical design and build section of this project, numerical analysis in the form of a computer simulation based on a modified inverted pendulum will also be carried out. This is currently been done using GNU Octave, and Open Source alternative for Matlab which runs well on Linux.
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