HOW THINGS WORK
SOMERSAULTING DOG
Introduction :-
We are going to demonstrate the working of a Dog which walks over
a certain distance, thereafter it crouches and then somersaults
to get back to initial position. Actually the Dog is driven by a
motor which is powered by a 2*1.5 volt Battery. The whole motion
is due to a peculiar shaped disc which coordinates the motion
between various elements of the mechanism.
Material Used :-
The body frame is made of aluminium and tin, as they are light and
the strength requirements are not too high. The disc is made of hard
plastic because it has to drive the slider.Gears are made of plastic.
Driving Mechanism :-
The top view of the entire mechanism is shown in Picture A.
PICTURE A
The basic driving mechanism is shown in the figure 1(a). The input to the
system comes from the motor in which Gear 1 is attached. Through
a set of gears(2 & 3) motion is transferred to Gear 4 . Both the
Gear 5 & Gear 6 is driven by Gear 4. Gear 7 drives the crank of
the 5-link walking mechanism, while Gear 5 drives the disc due
to which crouching and somersaulting is made possible.
----------- SIDE A******************************* SIDE B------------
Figure 1(a): TOP VIEW OF THE DRIVING MECHANISM
Figure 1(b): SIDE VIEW OF THE GEAR TRAIN
The disc :-
The pictorial view of the disc is shown in Picture B.
PICTURE B
The input to the disc comes from Gear 5 which in turn is driven by Gear 4.
The cam rotates in the clockwise direction as seen from side A.
The disc is attached to a special type of cam as shown in the
figure 2. The cam has two distinguishable zone.
Figure 2: THE CAM SHOWING WALKING AND CROUCHING ZONE
- Walking zone : The cam rotates in the clockwise direction.
A slider is attached to the cam.
In this zone the radius of the cam remains
constant. And so the slider remains where it is. This is
how crouching is avoided during walking.
- Crouching zone : In this zone the radius of the cam
keeps on increasing. Therefore the cam pushes the slider in
the forward direction. The rear part of the slider is attached
to the midpoint of the rear legs.Since the upper part of the rear
leg is stationary, so the lower part of the rear leg moves
in the forward direction due to slider movement and the dog crouches.
Walking Mechanism :-
The Gear position during walking is as shown in
figure 3.
Figure 3: GEAR POSITION DURING WALKING
The disc has a peculiar shape such that during walking it pushes the shaft
inwards and hence it compresses
the spring loaded shaft driven by Gear 6 and thus Gear 6 engages with
Gear 7 which in turn drives the crank of the walking mechanism. The crank
is rotating in the anticlockwise direction. The walking
mechanism is a 5-link mechanism (shown in fig. 4) between the front and the
rear legs (shown as shaded) where the input motion from link 7 (integral
with gear 7) is first transferred to
the front legs which in this case is the link 8 and then
to link 11 on which the rear legs are attached via coupler(link 9). Both the
link 8 & link 11 (front and rear legs) are executing to and fro motion.
Figure 4:THE WALKING MECHANISM
Crouching Mechanism :-
The overall mechanism of the system during walking, crouching and
somersaulting is shown in the figure 5.
Figure 5: WALKING AND SOMERSAULTING MECHANISM
The picture showing the slider-cam mechanism is shown in Picture C.
PICTURE C
During walking the cam is rotating in the walking zone. In this zone
the radius of the cam is constant. So the slider(link 10) remains stationary.
The Gear position during crouching and somersaulting is shown in
the figure 6.
During crouching the disc releases Gear 6. Due to spring Gear 6 comes
back to normal position and thus it disengages with Gear 7. Since
Gear 7 was driving the crank(link 7) of the walking mechanism, so
the Dog stops walking.
Figure 6:GEAR TRAIN DURING CROUCHING AND SOMERSAULTING
The crouching mechanism is driven by Gear 5 which is the input to the
disc. The cam is operating in crouching zone. Now in crouching the
radius of the disc is increasing. Since the disc is rotating in the
clockwise direction. So it pulls the slider in the forward direction.
As the slider goes in the forward direction and the upper end of the
rear legs are stationary, so the rear legs go in the forward direction
and therefore they crouch upto the Somersault point.
Somersaulting :-
The force diagram during somersaulting is as shown in figure 6.
Figure :7FORCE DIAGRAM DURING SOMERSAULT
During crouching the extension spring(See fig. 7) is extended and that's
how it creates large elastic forces in the backward direction. Now when
the slider reaches the somersault point of the disc, the contact between
the disc and the slider breaks. The spring is stretched in the crouching
zone due to which there is a large spring force
acting in the backward direction. As the contact between the slider and
the disc breaks, the supporting force acting against the spring force
drops to zero, due to which the rear legs(link 11) try to
come back to normal position. So the rear legs exert a huge force
on the ground. But since the rear legs are in contact
with the ground, the ground also exerts force on the legs.
so the whole body of the dog somersaults in the
direction shown. The initial tension in the extension spring is
adjusted with the help of a screw, so that it can stay upright after somersaulting.
Special Comments :-
- The external covering of the Dog is made of soft, spongy material
(particularly at the legs). This is meant for absorbing(damping) the impact
shocks due to the landing after the somersault.
- The number of somersaults in the air can be changed by adjusting the
initial tension in the extension spring, thereby tinkering with the
somersault torque.
- The considerations for using the plastic gears are as follows:-
- Load is not too large
- Ease of fabrication
- Economical in large scale manufacturing
- Light weight
PROJECT TEAM
Dilip Kumar Sah (97119)
Alok Tiwari (97033)
Amit Kumar (97042)