with most of the vehicle designs on the site the tractor has a
timber chassis and uses steel components locally
where strength and toughness is needed - most notably for the
drive transmission, axle, steering and braking components.
- The tractor wheels are conventional turf tyre types - 16x6.50-8 at the
front (from Northern Tool - see image below right) and 18x8.50-8 at
the rear. The seating is positioned above the rear wheels to ensure good
weight over the rear drive for traction. Four 12V 38AmpH or two
75AmpH rechargeable lead-acid batteries can be fitted and are housed low and
forward of the rear axle in the tractor chassis and contribute to
keeping the COG low and maintain a
proportion of down-load over the front wheels to give adequate
steering traction. There is enough battery capacity to
give about two hours continuous running time between charges,
but this depends on loading off course.
used a drive design very similar to that on the electric
Voiturette, but this time
geared down to give a slower top speed - about 6-7 mph so that
much more of the motor power goes into drive torque at the
wheels. Each wheel is driven by its own 24V 660W DC PM electric
motor through a permanently engaged two stage roller chain
transmission (approx 20:1 reduction).
With this arrangement I
should get rear wheel drive forces of about 55kgf (120 lbf) at
the motors' rated torque/current output and up to two or three
times this this for short duration pulls as the motors approach
stall - plenty
for hauling a small trailer about the garden and for operation
on modest gradients. Higher drive forces than these will
exceed the traction limits of the turf tyres and are not needed
on this small machine. The effect of higher drive torques on the
DIY transmission stresses would also need to be watched for
higher power motors.
The single DC controller / double motor drive produces very
effective differential behaviour on the rear drive wheels and
the tractor has no problem turning at its full steering lock.
The inboard wheel drive torque does rise during turning as it
slows from its natural speed however this is not sufficient to
affect the steering under most driving conditions. In the
unlikely event that differential speed control is needed on the
rear wheels to aid tight turning the simplest and most
cost-effective way to achieve this is on this small machine is
to operate the rear disc brakes independently to hold back the
drive to the inboard rear wheel.
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