Project

# Title Team Members TA Documents Sponsor
18 S-band Radar Altimeter
 Bobby Sommers
Elliot Rubin
Rayan Nehme
 Koushik Udayachandran design_document1.pdf
final_paper1.pdf
photo1.png
presentation1.pdf
proposal1.pdf
proposal2.pdf
video
Problem:
Currently, hobbyist RC aircraft and civil drones rely on GPS and barometers for altitude measurements. While these methods are reliable and accurate, they may not tell the operator the full story. GPS is a line of sight system and does not work when the receiver is obscured by terrain or buildings. Barometers read air pressure, but will not measure the distance between an aircraft and terrain. A radar altimeter would provide low-flying drones and RC aircraft with accurate altitude measurements relative to terrain.

Solution Overview:
Our solution relies on a FMCW (frequency modulated continuous wave) S-band radar altimeter powered off of an internal battery. The radar altimeter will be mounted to the bottom of the drone and will use the 2.4GHz ISM band in its operation.

Solution Components:

Processing Unit:
The processing unit will consist of a microcontroller, barometric altimeter, and an SD card slot. The microcontroller will calculate the range to terrain based on the doppler shift from the radar and will log this information to the SD card. It will also record the altitude measured via the barometric altimeter to compare with the radar measurement. Finally, the microcontroller will generate the control signal for the FMCW waveform.

Radar Unit:
The radar unit will consist of two submodules: the transmitter and the receiver.

The transmitter performs frequency modulation using a VCO (voltage controlled oscillator) with a tune voltage generated by the microcontroller. This tune voltage is used to sweep the VCO frequency and creates an FM waveform. A PA (power amplifier) is used to increase the transmit power and is connected to the Tx patch antenna. The Rx patch array receives the reflected signal, amplifies it through a LNA (low noise amplifier), down converts it with a mixer, and provides the demodulated signal to the processing unit.

Power Unit:
The power unit consists of a shielded switching converter to provide DC supply voltage to the other units. This DC power will be regulated by a LDO (low dropout regulator) to provide low-noise power to sensitive components such as the LNA and the VCO.

Criterion for Success:
Our radar altimeter should accurately and precisely measure distance within 1m and record measurement data to a SD card for post processing. It should have a minimum range of 20 m.

Alternatives:
There are several 24GHz radar altimeters designed for use on UAVs, but they are more expensive and are not targeted to consumers. Development boards from semiconductor companies and vendors such as Adafruit and Seed also operate in the 24GHz band, but have very limited range (<10 m).

Active Cell Balancing for Solar Vehicle Battery Pack

Tara D'Souza, John Han, Rohan Kamatar

Featured Project

# Problem

Illini Solar Car (ISC) utilizes lithium ion battery packs with 28 series modules of 15 parallel cells each. In order to ensure safe operation, each battery cell must remain in its safe voltage operating range (2.5 - 4.2 V). Currently, all modules charge and discharge simultaneously. If any single module reaches 4.2V while charging, or 2.5V while discharging, the car must stop charging or discharging, respectively. During normal use, it is natural for the modules to become unbalanced. As the pack grows more unbalanced, the capacity of the entire battery pack decreases as it can only charge and discharge to the range of the lowest capacity module. An actively balanced battery box would ensure that we utilize all possible charge during the race, up to 5% more charge based on previous calculations.

# Solution Overview

We will implement active balancing which will redistribute charge in order to fully utilize the capacity of every module. This system will be verified within a test battery box so that it can be incorporated into future solar vehicles.

Solution Components:

- Test Battery Box (Hardware): The test battery box provides an interface to test new battery management circuitry and active balancing.

- Battery Sensors (Hardware): The current battery sensors for ISC do not include hardware necessary for active balancing. The revised PCB will include the active balancing components proposed below while also including voltage and temperature sensing for each cell.

- Active Balancing Circuit (Hardware): The active balancing circuit includes a switching regulator IC, transformers, and the cell voltage monitors.

- BMS Test firmware (Software): The Battery Management System requires new firmware to control and test active balancing.

# Criterion for Success

- Charge can be redistributed from one module to another during discharge and charge, to be demonstrated by collected data of cell voltages over time.

- BMS can control balancing.

- The battery pack should always be kept within safe operating conditions.

- Test battery box provides a safe and usable platform for future tests.