Re: [mowbot] Mowbot

Dominic Peterson (d.peterson nospam at
Wed, 25 Sep 1996 16:57:37 +1000 (EST)

Ron wrote:
>How about the reciprcating blade out of a hedge trimmer or a reel mower?
>Golf courses use gangs of reel mowers towed behind carts to mow the corse.
>Highway departments and farmers use sicle bar mowers for trimming realy
>badly overgrown areas. These both seem less power hungry than a highspeed
>blade. Less likly to fling a rock in some kids eye too. The earlier
>estimates for mowtime would have to be adjusted if we have to stop every
>couple of hours to charge up the battery for the blade.

Yes, I'd noticed that the REALLY big mowing jobs (excluding the
rough-and-ready 'slasher' type jobs) are NOT done with rotary mowers but
with one or another type of (for want of a better term) "slicing" cutters
eg reels, sickle-bar etc. Look at large combine harvesters - huge
sickle-bar cutter across the front.

Warning: Bad ASCII art follows - wear brain protection :-)
| 5mm |
_ _ _ _ _ __ _
| \ / \ / \ / \ / | _ _
| \ / \ / \ / \ / | 20mm /_\___/_\___
| \/ \/ \/ ..... \/ | _ <-moves-> \_/ \_/
| | Cross-section through
|_______________________ _________| upper & lower plates

Two plates like this (say 6mm thick) are mounted on top of each other with
one (probably the top) fixed and the other able to oscillate left-right by
the tooth width (5mm in the example). Lots of nice cutting edges but all
only accessible to grass sized things. I have a beard-trimmer with a very
similar cutter (smaller scale of course - I don't have Paul Bunyan's beard!
:-) and I can run my fingers over the cutter while it's running (ie it's
safe) and it has a (detachable) comb that fits over the top to set cutting
length. Initial impressions are that something very similar could do a
nice job on grass. It should be fairly power efficient too as the moving
elements are relatively light and moving fairly slowly and the cutting
acting is 'two cutting edge scissor-type' rather than 'single, fast-moving
edge cutting against the inertia of the blade of grass'.

The most difficult part of this is finding one or making it from scratch.
I'm going to do a bit of experimenting (aka skinning my knuckles and
reminding myself about my limited metal-working skills) and I'll report
back to the list with my results.

>My neighbor has one of those electric mowers that runs on a battery. I'll
>have to ask him how long it will run before it needs to be recharged.
>Does anyone know what the power requirement is for one of those electric
>Once we have that we should be able to do some battery capacity calculations
>to see what kind of battery we would need.

I've seen some truly SCARY numbers quoted for estimated power consumption
here over the last few days. 10A at 12V is an awful lot! I think
something below 5A continuous for all of the system (not just cutters, but
drive etc) should be easily achievable. Automotive starter motors draw
something like 40-50A for a short time while turning over a whole engine.
Surely we don't need 20% of that effort just to cut some grass and move a
(hopefully) light mower around?

Anyway, enough ramblings for now.


Dominic Peterson Email: d.peterson nospam at
(c) 1996 - Copyright remains with the author unless explicitly stated
-- All opinions are mine and do not reflect those of the University --