This document summarizes the design process of a bio-inspired walking robot. It began with four conceptual designs, two using one servo and two using multiple servos. After analysis, a design mimicking a seal gait was selected as the simplest. Statics and kinematics analysis determined a 2:1 gear ratio was needed to provide sufficient torque. The robot was built, but initially the servo could not handle the weight. Weight was reduced and arm lengths adjusted, allowing it to successfully walk 4.9 meters as required. The analysis upfront helped produce a simple, robust design that performed well.

1. Bio-Inspired Design
Blake Johnson
Abstract— The goal of this paper is to obtain a complete
understanding of the concepts required in the design of a bio-
inspired robot. The general concept and thinking behind the
project, as well as the analysis of the reason behind the success
of the project is the essential purpose of this project. Statics and
kinematics were the main mathematical base to the entirety of
the project. The ability to realize how each part was going to
react with one another was the most essential ability to obtain
during the process of the design. The goal of this paper is to
go over the design process, and to highlight the entire thought
process of the entire design process.
I. INTRODUCTION
For the third project in MMAE 232 - Design for Innova-
tion, it was required that we design a bio-inspired walking
robot (see Fig. 9). The robot had to use a servo, or a system
of servos, and had to resemble a gait of a biological being.
The robot had to be able to walk 4.9m autonomously, and
once it completed the 4.9m walk, we had to pick it up and
move it to the start line to complete its second trial. The
design also had to be disassembled, meaning glue could not
be used to hold any of the electronics in place.
II. CONCEPT GENERATION AND EVALUATION
Our four original designs had two that consisted of one
continuous servo, making it as simple as possible for the
design process (see figs. 2 and 3). One of them was going
to represent the gait of a duck, and the other represented a
seal. The other two designs were a little more difficult(see
figs. 4 and 5). The design with a similar gait plot to a dog
was going to consist of four servos that would move each
leg individually (see gait 3). The design that resembles a
gorilla was going to move with one continuous servo in the
front with two servos that work individually in the back. By
further inspection of both the gorilla and the dog designs,
we realized it was going to be much more difficult to make
these two designs. The timing of the gorilla gait was going to
be very difficult to time out. And the dog gait may have had
to use eight servos instead of four in order to work properly.
We then did a Pugh chart to determine the strengths and
weaknesses of each potential design (see Table 1). We then
decided that the seal gait was going to be the easiest to
mimic, and it was also going to require the least amount of
time to design.
III. ANALYSIS
The most important part of the design process was deter-
mining whether the system was going to be statically stable
in all phases of the entire gait. On top of this, the amount
of torque necessary to move the design had to be found as
well. This was found using a free body diagram (see fig. 8).
Fig. 1. Caption minutes after the successful test
TABLE I
PUGH CHART
Criteria Weight Seal Duck Dog Gorilla
Mass 3 +1 +1 -1 -1
Stability 2 +1 -1 +1 0
Posture 1 +1 -1 0 0
Speed 1 0 +1 +1 +1
Total +3 0 +1 0
Weighted Total +6 +1 0 -2
This free body diagram shows the very instant that the body
begins to lift. Since we made the base so long, we knew that
it would never come completely off the ground. This was a
design feature that allowed us to use two arms to propel the
design forward. Once the design is lifted off of the ground,
the only force that has to be overcome is friction. Since most
of the force will be resting on the arms, we knew that the
frictional force was going to be much less than the force
necessary to lift. Therefore, the distance (d) from the center
of mass to the reaction force (FR) is 150mm. The distance

2. Fig. 2. Original drawing of the seal
Fig. 3. Original drawing of the duck
Fig. 4. Original drawing of the dog
Fig. 5. Original drawing of the gorilla

3. from the force necessary to lift (Farm), and the reaction force
is 220mm. If you do a sum of the moments equation, you
will be able to find the force necessary to lift the object off
the ground. The weight of the project including the servo is
about 9.8N:
M = −((Fmg) ∗ d) + ((Farm) ∗ d) (1)
0 = −(9.8N ∗ 150mm) + (Farm ∗ 220mm)
You find that Farm = 6.68N. This is the maximum force
allowed to keep static equilibrium. Therefore in order to
break static equilibrium, you need any force greater than
6.68N. In order to find the minimum torque necessary, you
will use this number in the equation used in the torque free
body diagram (see fig. 9). In order to find the minimum
torque required to lift the seal’s body, you will use:
Tneeded = Farm ∗ larm ∗ sin(θ) (2)
Tneeded = 6.68N ∗ 100mm ∗ sin(49)
Tneeded = 505Nmm
You find that the torque necessary is about 500Nmm. This
is well over the maximum torque that the servo can handle.
We then decided to use gears in order to increase the amount
of torque that the servo can apply to the arm. The gear ratio
we decided to use was 2:1, and we placed the smaller gear
on the servo. This would in turn slow down the speed of
the motor, yet would double the amount of torque that can
be applied to the arms. Now that we found that we need
500Nmm of torque to lift the body, the 2:1 ratio will cause
the amount of torque that was needed by the servo motor to
be 250Nmm, which is well under the maximum allowable
torque given by the servo.
IV. EXPERIMENTAL RESULTS
The project went relatively smooth, other than the need
to cut weight. When the entire design was put together, the
servo could not handle the torque necessary to rotate. We
decided to scrap most of the design that was unnecessary to
motion. We also cut weight off of pieces that were oversized
and unnecessary as well. By the time we got the design to
move, we had cut out everything but the necessary pieces
(see fig. 1). As you can see in the figure, we didn’t precisely
cut anything off of the project. All that was necessary for
motion was the base, to stabilize the design during motion,
the gears, the two pieces that held the servo, the two pieces
that stabilized the rod, and the arms, which pulled the design
forward. After the weight was cut, the design began to move,
but it rotated to the right as it moved forward. So we began to
shave down the arms to make sure they were the exact same
length and were only in contact with the floor at the same
exact time, otherwise it was going to rotate in the direction of
the arm that had less contact with the floor. After these minor
adjustments we were able to get the design to perpetuate
forward with almost no rotation. Our design walked the 4.9m
in both directions with no issue. I had more confidence in
this project than the other two we had done earlier in the
Fig. 6. Convex Contact Polygon of the seal
Fig. 7. Gait plot of the seal

4.
Fig. 8. Free Body Diagram of the Seal
Fig. 9. Free Body Diagram of the arm
semester. This project actually took less time to design than
the other two had as well.
V. DISCUSSION
As stated previously, we had issues with the weight of
the design, and the contact time for both arms, but other
than this, we had no issues with the design. The reasoning
for the issues with the weight is because we underestimated
the amount of weight that was going to be involved in the
design. Then when we cut the arms, which was done because
they were too long, we had issues with the amount of time
the two were in contact with the ground. After these two
were fixed, the project needed no adjustments. The servo
was continuous so there was no timing involved. The project
went as expected after the minor adjustments.
VI. CONCLUSIONS
This project went as smoothly as it possibly could have.
The key to the simplicity of this project had to do with the
analysis done prior to the project being designed. As soon
as we figured out what we wanted to do for the project, we
made an effort to achieve simplicity throughout the entire
design process. This attempt for simplicity made any issues
extremely easy to fix. Any issues that we ran into had no
effect on the rest of the project. This feature in the design
process is something that we can use in the future. It makes
for less complications, which allows for less time wasted.
VII. MATLAB CODE
V1=[2 3.5 5 6.56 8 9.5 11 12]; I1=1/1000*[13.86
23.93 34.15 44.96 54.87 65.5 76.3 83.6]; V2=[1.59
2.9 3.8 5.1 6.51 7.88 8.54 10.37]; I2=1/1000*[11.06
19.75 25.79 34.5 44.06 53.51 58.16 71]; V3=[2.12
3.22 4.25 5.16 7.28 8.22 9.58 10]; I3=1/1000*[14.59
21.96 28.9 35.01 49.43 55.96 65.48 68.6]; V4=[1.96
3.1 4.72 6.21 7.2 8.53 9.5 10.25];I4=1/1000*[13.52
21.08 31.94 42.01 48.87 58.04 65 70.3]; V5=[2.9
4.04 5.49 6.47 8.14 9.45 10.87 11.65]; I5=1/1000*[20
27.65 37.6 44.39 56.02 65.36 75.5 81.3]; figure;
plot(I1,V1,’or’,I2,V2,’sk’,I3,V3,’*b’,I4,V4,’m
, I5, V 5, >
g )ylabel( AppliedV oltage[V ] , FontSize , 14)xlabel( MeasuredCurr