Re: [mowbot] New section to Mowbot web site

Dominic Peterson (d.peterson nospam at
Thu, 03 Oct 1996 16:27:28 +1000 (EST)

Dave wrote:
>I've added an Experiments section to the Mowbot home page.

Good idea & nice photos of your experiment, Dave.

>I have put up information about using a hedge trimmer for grass cutting

The pictures illustrate the problem with using a cutter of that size. I
would estimate from the photo that the teeth on the fixed (lower) comb are
on about 20mm centres. Seen as a x-section through one pair of teeth
(upper and lower)(most definitely NOT to scale):

________________ |<---- 20 mm --->| ________________
/ fixed blade \ [] [] / \
/__________________\ [] [] /__________________\
------------------ [] []
\ moving ----> / [] []
\______________/ [] []
[] [] <-- grass blade 2
grass blade 1 --> [] []
[] []

It's fairly easy (??) to see from this diagram that blade of grass 1 is
just going to get folded over but blade 2 will almost definitely get cut.
If the 20mm dimension is reduced to more like 4 to 5 mm then performance on
grass will be much (much) better. And at those sort of spacings very
little is going to get in other than grass - a slotted guide/separator in
front of the cutter would exclude loose twigs leaves etc and make it safer
again. Go to a store and look at a Phillips beard trimmer - it has an
adjustable guide over a comb cutter - all we (I?) need is the same thing
scaled up by about 5:1 . I'm still working on making a cutter out of
readily available materials with normal tools but other things (like work &
study) keep cutting into my experimenting time :-). The only readily
available cutter of that sort of dimension that I can think of is a
shearing clipper (Dave, you're an Aussie - want to get into a
wide-comb/narrow-comb battle :-). For the benefit of non-Aussies, I'm
talking here about sheep shearing.

I'll keep at my experiments, as time permits, and report back with progress
(and some photos for the Experiment web-page).

Best regards,

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 --