Electronics

Conceptual Design

The electronic system diagram represents a starting point for the development of an electronic system.

Prior to this system design, it was established that there was a need for a computer controller with memory.

The computer controller requires an interface, with inputs from sensors.

IR range finders, rate gyros and tacometers were chosen as sensors following an early brainstorming session and much research.

 

 

Controller

A Personal Data Assistant was determined to be a promising controller.

Book Reference: PDA Robotics. (Thanks to Pembroke College Library).

An HP iPAQ was chosen but found not to have a USB host.

A Balloon Board is currently being considered.

A complete system solution is provided by the National Instruments Compact RIO product line and has been considered.

 

 

Interface

USB I/O 24 card:

 

Bandwidth Budget 8/11/4:

Component Samples/s Bits Quantity Bandwidth
IR range finder ADC 4760 1 1 4760
Gyros ADC 3060 1 1 3060
IR tacometers 1600 1 4 6400
Radio PWM receiver 256000 1 2 512000
       
ESC PWM outputs 256000 1 2 512000
IR range finder ADC clock 4760 1 1 4760
Gyro ADC clock 3060 1 1 3060
       
TOTAL:       1046040

 

 

 

 

 

 

 

 

This budget prompted a meeting with Peter Long and consideration of alternatives to direct PWM.

 

 

Sensors

Infra-red range finders:

We have conducted tests on our preferred IR range finder using CUED's Inverted Pendulum experiment apparatus (thanks to Dave Gautrey).

The results both take the form of screenshots of the graphing software and text files containing data for analysis.

The full range of the sensors is 20cm to 80cm. The critical range for the unicycle's geometry is 36.5cm to 51cm.

 

Infra-red detectors (Tachometers):

 

Ultrasonic range finders:

Discounted as not fast enough response.

 

Electronic Compass:

Still under consideration due to requirements and possible interference effects.

 

Inclinometers:

Avoided due to slow response and interaction of lateral accelerations.

 

Tilt switches:

See above, but may be used to confirm attitude under low acceleration conditions.

 

 

Gyros

Rate Gyros:

Glen Vinnicombe in the Engineering Department has given us three Gyros:

We have conducted tests to investigate the output of these gyros:

The oscilloscope plots of the tests are given here as graphics files:

new gyro calibration results

preliminary test

 

fast frequency test

 

slow frequency test

 

multifrequency test

 

 

Drive System

Several options are available for the drive system: the connection between the computer and each of the two motors.

The image and table below summarise the characteristics of each option.

ESC = Electronic Speed Controller                                                    

 

No.  Computer Controller Bandwidth  Response time Processing  ESC Cost  Hardware  Debugging
 1)  Very high for PWM: 256kbps Max  100ms Intensive  40  1 stage  Limited internal
 2)  Medium: 9.6kbps (RS232)  10ms Medium  150  1 stage  Limited
 3)  Low: 30Hz min  100ms stock Minimal  60  2 stages  Good (analogue)
 4)  Low: 30Hz min  100ms Minimal  40  3 stages  OK (ADC)

It was decided in a meeting that option 3) is most promising and worth investigating further.

Option 3) has been incorporated into the electronic system diagram.

 

Research