Re: [mowbot] A heavy mower

Dave Everett (deverett nospam at
Wed, 16 Jul 1997 17:56:45 +1000

At 09:07 AM 7/14/97 +0000, you wrote:
>> Date: Sat, 12 Jul 1997 22:48:13 +1000
>> To: mowbot nospam at
>> From: Dave Everett <deverett nospam at>
>> Subject: Re: [mowbot] A heavy mower
>> Reply-to: mowbot nospam at

>Hi Dave, thanks for your interest. This weekend I replaced the
>sloppy steering connection with a firmer assembly, and the thing
>holds direction better; it used to wander about unpredictably.
>> Have you considered using 4 mikes, like a doppler direction finding
>> array? The mikes would be spaced in a square.

>Could you please explain how I could determine direction with four
>mikes in a square? I doubt I could measure any Doppler effects at
>the 14 cm/sec current crawl speed.

I just meant 'like a doppler direction finding array', not _actually_ a
doppler array :-)

By polling the 4 mikes and determining the signal strength from each
you would be able to determine the direction of the 17khz signal. I
realise that that is basically what you're doing now, but I got the
impression that the current version wasn't as accurate as you'd like.
Also using 4 mikes allows you to determine the robots orientation as well.
Actually it is really a doppler system as the signal would be received at
slightly different times due to orientation.

Consider the following:



The signal S will be received first by mike 4 then 3, 2, 1.

>> What are the chances of you mounting the XT on the robot to avoid the
>> comms transmission problems?
>Mounting a computer on-board is, at the moment, beyond my budget.
>Good idea though.

I am assuming that the XT is just for the robot. I'm sure you have another
computer there. If you strip out the motherboard, IDE controller, Comms
card, hard and floppy drives they could be mounted on the robot and a power
supply constructed to run off batteries. I know of another roboticist who
has done just this. I'll see if I can get some more information for you.
Even if you don't want to do this I'm sure the information would be useful

The other approach would be to use an old XT laptop, they usually go for
Dave Everett.