The purpose of this section is to detail the mechanical
construction of the Lawnmower’s mounting frame and how
the lawnmower and wheelchair parts are mounted to it.
This is intended as a guide to build your own RC Mower,
however I won’t be posting up CAD plans for a few main
What IS here is a detailed description of the frame
design and construction to provide plenty of
‘inspiration’ for your own creation.
Part 1 - Donor
mower chosen for the job was a Murray low profile
mulching mower powered by a Briggs n Stratton 5hp 4
purchased off ebay for a measly $200 and was in pretty
it was a great starting point for the mower project as
it was low profile (no catcher - plenty of room for
batteries), powerful, mechanically simple and had a
large cutting area (20" if I recall).
like a charm and I think I made the right decision.
convert it over, no irreversible modifications were done
to it at all. If desired, I could easily convert it back
to it's original form, but why the hell would I want to
The first pic shows
the low profile of the mower with the wheels off.
The mower is quite
wide and in the 2nd pic you can see the beefy
5hp Briggs & Stratton 4 stroke (it's BIG!).
Lastly is a shot with
the handle removed (I just unhooked the cables and
removed the 2 locking pins securing them to the
Notice the 4 wheel
independent height adjustment... This later turned
out to be a pain in the ass but I think I have a
are the mods I had to do to the mower to get it ready
for the 'transplant':
Firstly the wheels disappeared.
removed the handles and carefully unhooked the
engine cut and accelerator cables from the motor.
Lastly I removed the two rear height adjusters
(secured by a single nut and bolt) and reversed them
to they faced the same way as the ones on the front
(see pics below). This was done so I could fit the
wheelchair motors & Wheels as close to the body as
...And that's all I did to
The chair was acquired
from a mate of my Dad's who sells and services
wheelchairs and scooters. This old thing had been
retired and needed a make over so we picked it up for
It even had a charge in
it. I kept it together during the testing stage of the
Radio Control to Joystick converter I built (see the
ELECTRONICS section). Once
I was happy with that I pulled it apart!
(I forgot to get pics of
it 100% complete - whoops!)
Not really much to tell
apart from saying I stripped all the electrical gear out
of the frame:
NOTE - When you
remove the wiring loom, mark where each plug goes with a
pen or sticker for easy assembly later on!
The left hand motor
assembly (with wheelie bar removed):
... And that's all for the
wheelchair. I didn't need to modify anything apart from
the Radio Control interface, so now it's on to...
Part 2 - Frame
Ok, first step of the
frame was the main rectangular chassis rails.
Material used was a square
steel 25mm tube (20mm inner diameter). To build the
entire frame, I used approx 5.5metres of the stuff.
When determining what the
width should be, I made mine so that the overall width
of the chassis rails is the same width as the distance
between the base of the axles for the wheels on the
lawnmower. See 5th pic below.. HOWEVER, check if this
width will also clear the mower motor and other
accessories. Mine cleared nicely.
Even more importantly is
to choose the overall length of the chassis rails
VERY CAREFULLY. Consider the following points when
At all times/height
adjustments the front swivel wheels must not touch
the body of the mower
The height adjustment
on my mower was 70mm from top to bottom, but at the
half way mark, it also shifted the mower back 15mm.
Make sure this does not interfere with the rear
drive motors or the front wheels
Make sure you add a
little extra to stick out the back. The motors end
up sticking way out, so it's better to have too much
than too little. I made a bit too short and ended up
having to cut out the rear bar and welding it on top
of the rail (see pics later).
FRONT WHEEL SUPPORTS
Next up was to fix the
rear wheels in place using clamps and weld the two
upright swivel wheel supports to the main rectangular
Yes my welding skills are
crap (self taught, gasless MIG - whaddaya expect???).
Yes there is a nasty lean on the left hand wheel
support. No - I don't really care.
These were welded slightly
back from the front edge of the frame for no particular
reason. It would be better to put them as far forward on
the frame as possible to get best usage out of the
After these are attached,
all that's required to fit the wheels is to drill holes
in the new mounts to match the existing holes in the
swivel mounts - easy!
MOWER SUPPORT STRUTS
Next I needed 4 identical
fixed struts extending down from the main chassis which
would somehow attach to the stub axels of the mower.
I wanted to be able to
remove the mower from the frame if I needed to so I came
up with the following setup:
Pics (left to right)
1 & 2:
4 of these brackets were cut from 20mm tube steel. The
brackets had two 5mm holes drilled on one face (for the
bolts) and the other face had a single 12mm hole to fit
the axle on the mower.
Illustrating how the rig attaches to the mower's
how the brackets attach to the upright struts (which
will be welded to the chassis)
5 & 6:
Fitting them to the chassis.
By now the chassis was
coming along nicely. It was now that once I started test
fitting everything, I decided that I needed a bit more
room to shift the wheelchair motors back a bit, so I had
to remove the rear horizontal bar and replace it with a
slightly longer one (50mm longer) which sat across the
top (see 1st pic below).
Then I trimmed the mower
support struts to be flush with the chassis:
The last structural
addition I felt this frame needed was and extra bit of
bracketry so I could use all 3 bolt holes on the
wheelchair motor mound brackets. They were 3 in a
triangle pattern and I felt that the motors would flex
too much if I only used two to mount them to the frame.
So, copying the same
angles as the bracket, I made these on the underside of
the chassis at the rear (again ignore the piss-poor
welding - I'm am amateur dammit!):
MUCH better! But...
there's something missing...
Now all we need is
something in the back to hold those 2 huge SLA
batteries, so here's what I did:
Pics (left to right)
First I welded another horizontal bar across the tops of
the rear support struts (make yours longer so they cover
the top of the support strut - not like mine!)
cut 2 x 20mm flat bar steel to length and bent the ends
up at right angles.
I welded them into the frame between the rear horizontal
bar and the new one I welded in the 1st pic. Make
sure the mower is at it's maximum height setting before
you do this!!!
I cut 2 more 20mm flat bar pieces to length and bent the
ends up at right angles, but they didn't go up as far as
the first 2.
Finally, I welded those to the first two flat bars
perpendicular to them. Voi la! A place for the
PLEASE MEASURE YOUR
BATTERIES TO MAKE SURE THEY'LL FIT BEFORE YOU GO DOING
THIS TO AVOID DISAPPOINTMENT.
As it turns out,
everything JUST cleared with about 5mm to spare on
either side, but please - measure twice - weld once!!!
Part 3 - Final
Ok, so now that all of the
fabrication work was done, it was time for a nice shiny
red paint job! I ground my crappy welding flat and
cleaned the oceans of splatter with the angle grinder :)
Beautiful! Then I
went to the hardware store and picked up some 20mm
furniture end caps (40c each). They fit perfectly and
with a gentle tap with a hammer, seated into the end of
the tube nicely.
Nice. Then I put the
wheels and motors on.
Then it was time to stick
the mower under the frame and attach it to the axles
with our custom made adaptors. 2 bolts per adaptor.
I was amazed at how rigid
the setup was. no sideways movement from the mower at
Batteries sit nicely in
their cage and don't foul on anything at any ride-height
Then finally, the wiring loom and electronic control box
go on (see the electronics
section for an updated pic with the receiver mounted
inside the control box)
DONE!!! A video of it in action is available in the downloads