802.11

**stu** · 15th April 2004, 21:17

LOL!!!

Mr Stu

**jim** · 16th April 2004, 08:43

Failsafe behaviour operates on a layer above the physical networking. The medium you use, whether 40Mhz, 459MHz, IR, bluetooth, 802.11, GSM, or tin cans and string is irrelevant. If any these standards have any built in safety then I wouldnt rely on it. The content of the message is all thats important. For example, a conventional failsafe module looks for pulses of between 1 and 2 milliseconds, 20 milliseconds apart - it doesnt care how they were transmitted.

**roger_plant** · 16th April 2004, 11:07

Some further info, the 802.11 g runs at 54 Mb/s but only up to about 10 mtrs range.
As the signal gets weaker it reduces its data rate from 54 to 48,24,12,6,3,and down to 1 Mb/s
At its max range of about 100 mtrs, its rate is only 1 Mb/s.
These measurements were taken from the Link Monitor on my laptop when I did the original tests.
1Mb/s is plenty fast enough for a robot data link, but not enough for decent video.
But, as I said before, only when the link is static, not moving.

**jim** · 16th April 2004, 15:39

I wish I had a laptop to test it with! I do know, however, that some people have managed to get WiFi signals in a moving aircraft 2500ft above a city, using a commerically available antenna, so perhaps we shouldnt write the idea off just yet.

http://quickwired.com/kallahar/stories/2003-Dec10/warflying.php http://quickwired.com/kallahar/stori.../warflying.php

**fluppet** · 16th April 2004, 16:14

There are universities who have set up 802.11 transmitters with range over 1km (dumb idea - shared bandwidth, anyone?) but I suspect the transmitter strength rules would be broken. Roger - I didnt have video in mind (although I know its been done in series past), but it would simplify the protocols for some telemetry. Theres no way I need 1Mbps, even for my dafter ideas. :-)

Out of interest, what do the house robots use for their cameras (assuming they dont record locally)?

Eddy - should be there, will look forward to chatting to you.

--
Fluppet

**storm** · 16th April 2004, 16:35

They record locally Andrew.

**fluppet** · 16th April 2004, 17:04

Ah. Thanks, Ed. Oh well, so much for that theory. :-)

What technology did the competitor (I want to say Lightning, but I think Im confused) use back in series three-ish to do the video feedback? Just curious.

--
Fluppet

**roger_plant** · 16th April 2004, 17:11

Jim, there is a lot of difference between picking up a WAP long enough to identify it and getting a continous signal to control a robot.
If you keep losing the signal your system will go into failsafe mode often and your robot will behave like a kangaroo.
The arena metal framework will play havoc with moving 2.4 or 5 Ghz WAP signals.
So will another metal robot moving near yours.
The signals reflecting off moving metal objects will add and cancel out all over the place.

Andrew, It is possible to get 10 Km with 802.11 using high gain directional aerials and standard power but only fixed point to fixed point.

I dont know what the H/Rs use for video links but the BBC have access to many channels for video transmission.

Both 1.3 and 2.4 Ghz 0.1 watt license exempt systems are available for all to use for video.
They have a range of about 400 mtrs using simple omnidirectional aerials. Cost under Â£100.

I am a radio ham and I use 1.2 and 2.4 Ghz (at 16 and 1 watt) links for my robot cameras, and get more than 30 miles line-of-sight easily.
I am allowed much higher power with the license.

**jim** · 16th April 2004, 17:50

Very true, Roger.

It would be fairly simple to do an experiment - we would need a WiFi enabled palmtop computer like an iPaq which could fit inside a robot chassis, and a WiFi laptop. We could then rig up a program for the iPaq to record data streamed from the laptop during a fight, preferably a fairly relaxed fight so theres less chance of damaging the iPaq. Does anyone have the right equipment to do this?