Recent Progress
Motor Control
- 11/7/14 Selecting a FET for the Commutation Driver
The main concern with using a FET for the high-low
configuration required for the brushless commutation is the gate
capacitance of the transistor. In order to limit this, one
of the primary specs that we looked at when choosing a FET was
the total gate charge QT. Another key attribute
of FETs are their RDS(on) value, which is a key
component for the power consumption the transistor utilizes.
After a few weeks of research, we came to the conclusion
that the
IRLB8748PbF transistor would be best
sutied for our application. Here are the key specs for
that transistor:
IRLB8748PbF
•RDS max=4.8 mΩ
•VDS max=30 V
•ID max= 44 A
•QG max= 23nC
- 10/27/14 Choosing A BLDC Motor Controller
After about over a week worth of research, team OBSCENE
came to the conclusion that the BLDC motor controller we will be
using is the Allegra A4690. The T4690 is a sensorless
communtation pre-driver with is controlled via a SPI bus and a
inputted PWM signal. The motor controller also outputs a
rotational speed sensing signal that allows feedback into an
external MCU that will be used for direct communication between
the motor control configuration and the CPU.
- 10/16/14 Decision On A Motor And
Configuration
After some research and premilinary testing of in-house
built trusters, Nick Schmidt came to the conclusion that we will
have to purchase new motors for our system moving forward.
Through research into thrusters that could generate enough
thrust with optimal cost and size, Team OBSCENE came to the
conclusion that the T100 by blue robics(URL below) would be
ideal for the ASV boat design. The T100 thrusters provide
about 5.2 lbf forward thrust while operating at 130 watts and
only weigh 0.65 lbs in air. The main benefit of using the
T100 thrusters versus other thrusters of equal magnitude is the
cost. Each individual T100 thruster cost $109, while some
competitors prices are $800 and higher. Also using these small and lightweight
motors would allow for the ASV to utilize a four motor square
configuration where each motor is set at a 45 degree angle
allowing for the vehicle to travel in any 2D direction.
However, the T100 are brushless motors, which means they have a
three phase configuration that requires precise timing and
accuracy. Instead of design an entire control system for
each individual phase, we decided to research prebuilt BLDC
motor control systems that would save our team hundreds of hours
of work for a minimal cost.
T100 Link:
http://www.bluerobotics.com/store/thrusters/t100-thruster/
RC Controller
- 10/28/14 Setting Up The RC Signal
Team OBSCENE has been working on an RC to serial
converter to be able to control the boat from a remote location,
at this moment the team is able to read in the RC signals
through the receiver to an Atmega168, and then output the pulse
widths to a terminal window over a TTL serial to an RS-232
serial using a MAX3232.
GPS/Compass
Image Processing
Central Processing Unit
- 10/09/2014 Installing the OS
Using the inherited I7 processor, and the x86 mini-ITX
motherboard, Team OBSCENE installed UBUNTU 14.10 for the CPU
operating system.