RE: [mowbot] Cordless lawn mower modification.

Dave Everett (deverett nospam at
Thu, 14 May 1998 17:44:53 +1000

At 09:27 AM 14-05-98 +0000, you wrote:
>My mower uses a threaded shaft and nut for the steering.
>The nut is mounted in a gymbal cage so it can swivel
>freely, otherwise things jam up.
>Position is not sensed; there are left and right limit
>switches, so it stops at a known position. I tried to
>make a center stop switch, but it was too much
>trouble. It would have been nice to command the
>center position and know it was travelling straight.

Drive the motor fully to one limit switch, then drive the motor the other
way counting each rotation of the shaft with an otpo until you hit the
other limit switch and divide by 2. You could then command any position on
the shaft and even periodically recalibrated the mechanism.

>I have recently upgraded my ultrasonic 17 kHz
>transponded so it works with much more power
>and no more frequency shift. I expect to be
>able to measure position with maybe one foot
>error max. I receive the signal at 20 meters
>distance with a 4:1 signal to noise ration.
Great! Love to see some photos and schematics when you have time.

Dave Everett

Mowbot Project Website