With the increase in the trend of using robots for all applications where human intervention may not be possible and where safety and cost are important factors, the necessity of robots that can traverse the battlefield without taking much damage is felt. Many solutions are proposed for such robots for battlefield use but they are very complicated and costly involving mechanical legs and crane like apparatus, but these are meant for support to soldier and very few designs focus purely on surveillance. This paper deals with the design and development of an armored robot with 2 degrees of freedom. The CAD model of the Robot has been made in Fusion 360 software at the Faculty of Technology and Engineering, the Maharaja Sayajirao University of Baroda. The proposed robot is a tank with no mechanical arms or legs and is cost effective using commercially available methods of manufacture.

Most of the robots in the market have bi-directional motion. So, for a better case it would be good to consider an omni-directional motion.

This website helped me understand the work case of these modern day wheels.

In the case of mechanical designing and strength of the model, it seemed important to design a strong and sturdy design, that is not broken down by any kind of attack or thrust on its surface.

Corran, R. S. (1983). Impact loading of plates — An experimental investigation. 

Mechanical Design

The structure of the robot can be divided into 3 parts,

1. Frame

2. Main Body (defensive plates)

3. Triangular Protrusions (extra armor)

In our prototype, the frame is made from Mild Steel angle sections with dimensions 25 x 25 x 5 millimeters. The angle sections are welded together by MMAW using mild steel electrode and subsequently grinded to obtain smooth surface to form a cuboidal shape of dimensions given below. This was important to provide core structural rigidity to the body and will later act as a chassis for the body and armor plating.

For initial testing, the body is made using mild steel plates of thickness 5 mm and is the main armor providing resistance to the internal sensors and electronics from direct impact. Plates of mild steel are directly welded to the frame using methods similar to the ones used to weld angle sections together. The 5 mm plates provide considerable armor against small projectiles. The Top plate is Fitted using M10 bolts whose nuts are welded to the frame to maintain accessibility to the internal components. This was the initial prototype and further improvements to the armor can be carried out.

The Protrusions in the form of right-angle triangles of size 100 x 100 x 12 millimeters are welded to the side plates of the body. These provide excellent resistance against direct impact loads and offer some relief to the body by absorbing appreciable protection from projectiles.

Finally, the structure is ready. Shown below is a render of the structure design.

Design Calculations

Total weight (in KG) = density of steel x ((volume of 1 angle section x total angle sections used) + (volume of 1 plate x total plates used) + (volume of 1 triangle x total triangles used))

This is done to get an estimate of the weight of the structure and hence select the appropriate motor. Note that the actual weight will vary somewhat than the calculated value.

Static Loading

Load = permissible tensile strength x ((cross sectional area of angle section x 4) + (cross sectional area of plate x 4)

In actual practice, load capacity is much higher due to the welded joints and triangles.

Translation motors

Initially, geared DC motors were used in testing which resulted in poor performance and very low torque. The motors burned out due to such heavy load. Later, Planetary geared DC motors were used with RS735 motors and P219 gearbox with 19.2:1 gear ratio. These motors provided high torque and much better performance. However, they require a very high current posing difficulty in cooling and burning up wires.

Wheels

Mecanum wheels were used in the prototype to give an additional degree of freedom. These wheels provide sliding movements which is useful for good controllability. However, for rough terrain wheels can be changed to simple cylindrical wheels quite easily.

Control System

The Control System includes a microcontroller and Motor Driver Shield for controlling the motors.

The advantages of using a microcontroller are

1. Compact and reprogrammable unlike hardwired circuitry.

2. At a later stage inclusion of other features required by users may be added without any hassle.

3. Can be remotely operated and also automated.

The controller used for the purpose of the prototype was FlySkyiX6. 6channel, 2.4GHz radio with telemetry capability.

Microcontroller

The microcontroller employed is the Arduino UNO. It is a commonly used microcontroller in many prototype projects and is easily programmable. This was used as the resources for the Arduino UNO are easily available.

Power Source

Due to high current requirements, 12V LiPo batteries were used. 2 batteries were used due to high power draining motors and the circuit configurations which will be shown.

Working Logic[1]

The Logic behind the code is shown in the figure below. The motors can be run at different speeds to get different types of motions. This was the basic idea behind the circuitry and code(servo magazine, n.d).

Books:

1. Albert D. Helfrick & William D. Cooper, Modern Electronics Instrumentation and Measuring Instruments

2. M. Gopal, Control Systems (Principles and Design) 4e

Journals:

1.  Corran, R. S. (1983). Impact loading of plates — An experimental investigation,. International Journal of Impact Engineering,, 1(1), 3-22. https://doi.org/10.1016/0734-743X(83)90010-6.

2. Get rolling with Omni-directional wheels. Servo Magazine. (n.d.). Retrieved February 28, 2023, from https://www.servomagazine.com/magazine/article/get-rolling-with-omni-directional-wheels

3. Magare, A. E., Yelve, N. P., Kulkarni, A. U., Kudva, A. P., & Ipparthi, D. A. (2008). DESIGN, FABRICATION AND TESTING OF VERTICAL. A AND HORIZONTAL SURFACE TRAVERSING (VHST) ROBOT .

https://www.servomagazine.com/magazine/article/get-rolling-with-omni-directional-wheels

International Journal of Impact Engineering,, 1(1), 3-22. https://doi.org/10.1016/0734-743X(83)90010-6.