Discussions

This Autopilot system is the system fitted to the various UAV's designed and flown in Namibia for nature conservation and to support the anti-poaching programs there.

Have a look at the postings under Aircraft Platforms - by Joe and Gisela Noci in order to see these UAV's in action  -  Guppy, Hornbill and Kiwit.

Unlike the 'all in one' module offerings from various suppliers, this system consists of separate modules:

• IMU/INS - the inertial sensor pack forming the heart of the Inertial Navigation Sensor pack. It is based on an AVR processor, with a sensor sample rate of 200Hz. It contains 3 MEMS Digital Gyro's, a 3 axis digital accelerometer, and a Bosch BPM static pressur sensor. It has serial interface to the Airdata Module and the Magnetometer Module, as well as to the Host Autopilot Module. The IMU is fully temperature compensated and offset calibrated.

• Air Data Module - This module also contains an AVR processor, a Freescale static pressure sensor, a Freescale dynamic pressure sensor and another Bosh BMP static pressur sensor.This module is also fully temperature compensated.

• Magnetometer Module - This module also contains an AVR processor. It uses a Honeywell 3 Axis magnetometer chip, operating in balanced mode. The internal offset compensation strap is used, in a closed control loop, to create an opposing and equal magnetic field to the external ambient field. The current through this strap is then directly proportional to the external magnetic field.The advantage gained by this method is that the response to the external field is very linear and there is negligable temperature effect, a huge problem in conventional direct reading magnetometer circuits. This simplifies tremendously the temperature compensation requirements.

• GPS Module - a simple module, based on the Ublox LEAH range, updated as the next generation LEAH is realeased. It is a 4Hz update rate device.

• Autopilot Module - This module also is AVR processor based. It interfaces to all the servos via PWM outputs. It also receives PWM inputs from the RCS receiver for manual flight control, and manualy aided flight during flight control loop tuning. It has numerous serial I/O interfaces to air-to-ground datalink, IMU, Payload, rangefinder. It also contains an 8GB micro SD card for flight logging of all inertial data, A/C attitudes, etc, for post flight analysis, control loop tuning, etc. The Autopilot performs all navigation, guidance, flight plan managment, servo control and platform stabilisation, using data from all the attached sensors. It can also be fitted with IR horizon sensors and a second backup GPS for pitch/roll stability augmentation and position determination as a safety backup in the event of failure of any inertial sensor(s).

• The Ground Control Station - This is a PC based system and can be anything from a simple, reduced functionality Laptop based system, to the one depicted in the PDF files listed below. This system interfaces to a datalink antenna, with optional autotracker for the antenna, tracking theUAV in flight. It also interfaces to a dual video receiver, built into the video RX antenna. The video from the UAV camera is available in real time on the GCS, and can be recorded. A dedicated configurable Payload control panel is on the GPS operator position, allowing control of the UAV stablised camera, steering, setup, etc. All flight plans are prepared on the GCS, with a map of the flight regime, and all flight paths are shown, as well as the track flown. Numerous flight patterns can be selected, figure 8, square, straight line,  circle, loiter, point to point flight plan, etc. Aircraft control loop tuning is also done in real time, during flight, from the GCS. 

The reasons for implementing a multi-module solution are as follows.

Component obsolescence is a huge problem today, with some component lifetimes barely surviving 1 year. It is easier to stockpile components for the more complex applications, such as the IMU sensors, thereby permiiting extended support and production life for a specific part number module. Howeever, for the lower cost modules and components, it is often easier to redo the board, with the latest technology parts as needed, since the parts are inexpensive. The Airdata and Magnetometer module fall into these categories.

A further very compelling reason is to be able to split the sensor functions and spread them over the platform in optimal positions. For example, if the Magnetometer were located on the IMU, this poses a problem on electric motor platforms. Ideally the IMU should be reasonably close to the A/C center of gravity, but that means it is normally quite close to the drive motor and the thick wires carrying heavy currents to the motor ESC. The magnetic fields from these wires and the motor wreak havoc with the Magnetometer. Being on a seperate module we can now place the magnetometer towards the rear of the fuselage, keeping it bore-sighted with the IMU, out of stray magnetic fields. The same applies to the airdata module - it is sometimes easier to place the module in the wing close to the pitot-static tube, and bring wires from the wing into the fuselage via normal connector, than to have pneumatic pipes bring the air from the wing to the sensor in the fuselage.

This configuartion does not suit the very small and slim A/C, tiny gliders, etc, but the NamPilot is aimed at the higher performace, more safety critical applications, of larger UAV,s.

All these modules and the GCS, hardware, mechanical and electronic, were designed and built by me and all software created by my good wife, Gisela. The software includes all GCS software, and all aircraft flight control, guidance, navigation and INS software - She is a Boff!!

Attached are some photos of the modules, and some PDF files with more performance related data.

The Nampilot as fitted to Hornbill and Guppy is a packaged module, containing the sub-modules shown in the photos and PDF's.

Enjoy the Show...

imu_flyer_full.pdf

autop_flyer_full.pdf

gcs_flyer_full.pdf

Packaged Autopilot modules.