Steering - The front wheels of the Yard / Garden Tractor have a tilted king pin steering
geometry with Ackerman type linkages and are operated by the
steering wheel via a geared steering lever to lighten the effort
required to turn the front wheels. This steering geometry seems
to have reasonable self-straightening characteristics and tends
to return to center when the steering wheel is released. The
front beam axle is pivoted to help keep all four wheels of the
ground contact when operating on uneven surfaces - there is no
other suspension other than a compression spring I tried to
build into the seat support which I removed in the end in favour
of a more rigid support.
Electrical - A 150 Amp 24V motor speed controller is housed
under the tractor's ventilated front cover. The single 24V controller is
fully rated for drawing currents at 24V and is used to drive
both drive motors which are wired in parallel.
voltage systems could be considered, however a 36V system would
require either 3 or 6 x 12V batteries and would lead to problems
fitting them in the space available and a 48V system will lead
to additional un-needed expense in the motor and controller
selection. 24V DC provides an effective and inexpensive drive on
small EVs - a more cost-effective solution than an AC drive on
this size of tractor.
The controller gives the tractor its variable speed forward and
reverse drive and dynamic braking capability. My experience of
these electrical drives is that they give very smooth speed
control even when the vehicle is quite heavily loaded and it
makes for a smooth running, controllable tractor. Mechanically
independent braking is from two disc brakes incorporated into
the drive transmission although the dynamic braking from the
drive motors and 4-quadrant speed controller is effective in
slowing the tractor when the power is removed or reversed. As
mentioned above it would be possible to use separate brake
pedals for each rear wheel disc brake to aid tight turning - as
is the practise on larger tractors, at the moment there is a
single heel operated brake pedal for both wheels. I'm not sure
about the parking brake design yet but this will probably be a
lever operating the foot pedal.
tried to build in plenty of turning room at the front wheel
arches for the wheels and the tractor's turning circle is
therefore tight for good manoeuvring in the yard and garden. The
position of the tow bar allows quite acute angles between the
tractor and towed trailer.
I've gone for a British Racing Green painted finish
with matt black on the chassis and sub structures - the
green looked quite good in the rendered CAD images but red might
also be an attractive option.
The CAD rendered image on the left shows the tractor with chassis and bonnet
(hood) structure removed so that you can see the arrangement of
controller, batteries and rear wheel drive.
Detailed plans are now available for the Yard Tractor as part of the
full download or CDROM sets - see the
Plans Page here.
FREE preview versions of the assembly drawings for the yard
tractor are available here.
These do not include all the detailed part size drawings but may
give interested readers a feel for the design and of the construction
methods used. The complete plan set is available from the
(Note that some small lathe work will be required to complete this