M.
VAUGH
189
'The dynamometer as built was equipped to
furnish a tractive resistance for each horse which
could be varied from 60 to 350 pounds.'
'In order to test horses for their maximum effort
for short periods, a larger machine was built. This
dynamometer is shown in figs. 5 and 6. This operates
in essentially the same way as the smaller machine
just described but differs in constructional details
and in capacity. In the construction of the machine,
the chassis of a Nash quad four-wheel drive truck was
used. The engine of the truck was replaced with a
rotary pump so that the same train of gearing could
be used to drive the pump. The team in this case
is hitched to a double tree and only one set of weights
is used. The weights are made of reinforced con-
crete and normally rest upon the frame as shown.
Each of the weights may be attached to the weight
beam by turning a lock on the beam. The valve
controlling the discharge from the pump is so con-
nected to the weight beam that the valve is closed
when the beam is at the top. By this means the
forward movement of the truck is regulated auto-
matically so that the weights will always be lifted
while the dynamometer is in motion. This machine
has a maximum capacity of 4,100 pounds tractive
pull and a total weight of 10,000 pounds.'
'The machine shown in figs. 7 and 8 was also
built for testing horses for their maximum effort.
It is mounted on the rear of a Ford truck chassis and
as the engine was not removed, the truck can be
readily transported with its own power. The large
weights used are cast iron disks weighing 250 pounds
each. As many of these as desired may be attached
to the lifting cable. Small increments of weight
may be added by placing them in the space provided
between the two top weights. As shown in the
diagram (fig. 7) a pulley is so connected to the cables
that 500 pounds tractive effort is required on the
hitch to support each 250 pounds weight. This was
necessary in order to keep the total weight of the
machine as low as possible. A special sprocket
attaches to the rear of the worm shaft and drives
the pump by means of a roller chain. The lever
operating the pump discharge-valve is connected to
the weights, so that the valve is closed when
the weights are resting on the frame and wide -open
when the weights are at the top of their guides. By
this means, just enough resistance is automatically
applied at all times to the forward movement of the
dynamometer to keep the weights suspended. The
height at which the weights are carried depends upon
the speed of the team, the amount of weights attached
and the road surface, but is of no importance as
long as the weights are not touching either the top
or bottom of the guides.'
This machine has a maximum capacity of 3,200
pounds tractive pull and a total weight of 5,230
pounds. In order to get enough traction for average
road conditions, it is necessary to use skid chains on
the rear wheels and to put a skid under the front
wheels as shown in fig. 8. For loads very near the
maximum, additional weight is applied to the truck
body. This is usually accomplished by getting men
to stand on the platform.'
'For transportation it is only necessary to dis-
connect the tongue and skids, load them on the plat-
form and take off the roller chain which drives the
pump.'
'This type of machine has been further improved
by the addition of a three-speed auxiliary transmis-
sion with power take off attachment. This pro-
vides six forward speeds for transporting the machine,
and the power take off provides a more suitable
method of driving the pump; otherwise no important
changes have been made. The machine is illustrated
in fig. 9.'
It will be noted that the first dynamometer car
described by Collins and Caine and those described by
European workers are designed to give working
loads. The two latter described by Collins and
Caine are designed primarily to test maximum draft
ability, though by suitable adjustment it is possible
to use them for smaller loads also.
Broady and fellow workers used a tread mill
apparatus instead of a loading car, which they have
described in Missouri Bulletins 209 and 383. The
principle of the tread mill is that the backward push
of the animal's feet tends to move the travelling belt
on which the animal stands. This allows the animal
to stand in one place, which may be under a shelter.
In this way it is possible to have a uniform unvarying
footing on which the animal works and which is
independent of weather conditions. They first
experimented with loading the animal by using the
tread mill to drive an oil pump in the same way as
was used on the Iowa loading car by Collins and Caine.
This proved unsatisfactory, possibly due to the tread
mill being in bad mechanical repair. They
later loaded the animal by making it lift
weights.
M. A. Sharp described a simple traction dyna-
mometer for maximum draft tests in Vol. 22, No. 1,
dated January 1941, of the Agricultural Engineering
Journal. This consists essentially of a two-wheeled
cart made from the back axle of a lorry or car with a
platform and draft rig added to it. It also carries
a roller, on which a rope can be wound, fitted with
brake drums and brakes, which, when tightened,
resist the rotation of the roller. The roller is also
geared to a device, such as a car jack, which can be
used to progressively set the brakes as the roller
revolves. Rotation of the roller is secured by un-
winding the rope, the other end of which is fastened to
a tree or stake. The apparatus is prepared for a
test by winding the rope on the roller with the brakes
slack and the team or single animal hitched to the
C