Thread Tools
This thread is privately moderated by Jack Crossfire, who may elect to delete unwanted replies.
Aug 21, 2008, 06:21 PM
Registered User
Jack Crossfire's Avatar
Thread OP

Death of embedded computers

Before the first Gumstix, considered sending all the sensor data to the ground & doing all the control on the laptop. The idea seemed hopeless because the laptop didn't work, we didn't have fast radios, an embedded computer seemed like a 1 time purchase, but times have changed. Now the math.

A/D: 90 * (2 + 2 + 2 + 2 + 2 + 2 + 2)
Mag: 40 * (2 + 2 + 2)
GPS: 4 * (4 + 4 + 4 + 4 + 4 + 4 + 1)

Total down: 12800 bits/sec

The laptop would do all CCPM & send only PWM. The XBee sends 100 bytes at a time. Assuming it could work at the full 115200,

800/115200 + 800/115200 + some delay for the physical layer 1600/115200

28ms latency

You'd never reach that in wireless & there's a huge penalty for full duplex. The highest we ever got out of a PIC was 57600. Previously, the minimum delay for navigation was 50ms. All this would be done on the PIC.

Now what about doing control on the airframe & sending weights from the laptop. This would need a Netburner.

INS: 25 * (4 + 4 + 4)
GPS: 4 * (4 + 4 + 4 + 4 + 4 + 4)

Total down: 3168 bits/sec

Assuming 4 networks of 296 weights uploaded once a second, 50% compression, U need 80,000 bits/sec for the upstream.

Any laptop computation would unleash a massive amount of computing power for artificial intelligence. The barrier to entry would be much lower. The laptop would require new batteries eventually exceeding the cost of an airborne computer. It would require a lot of equipment. Things would be phased in.

1) No GPS downlink. Move airborn XBee to hardware UART. Move ground XBee to laptop. Connect sticks to laptop using former Xbee pins & protocol.

XBee Tx --------------> laptop Rx
XBee Rx <-------------- laptop Tx
Sticks ---------------> laptop UART 2

Laptop daughter board has MAX233 for XBee & sticks. Loss of sticks does not cause abort. Only loss of Xbee. Copter to ground must use resends to avoid IMU drift.

2) GPS downlink.

3) Neural networks on laptop.

4) Sticks ----- 72Mhz ---> laptop UART 2

Laptop daughter board has PIC for 72Mhz demodulation.

5) Convert laptop to embedded computer on the sticks.

It would require a monster assembly language campaign to get all the data off the aircraft. It would lock us into 2.4Ghz data but free up enough money for 900Mhz video.

Now some DVD burning secrets.

To create a large empty file for the UDF image:

dd if=/dev/zero of=$OUT_PATH bs=1024 seek=$SIZE_KB count=1

The laptop DVD writer does not really write. It probably needs a firmware update, Windows reinstallation, & functioning boot off USB to get Windows to work.
Last edited by Jack Crossfire; Aug 21, 2008 at 07:08 PM.
Sign up now
to remove ads between posts

Quick Reply
Thread Tools