The design of any robot should satisfy the following criteria

• Simplicity

• Compact
• Weightless
• Cost effective
• Easily re-configurable
• Motors with high torque
• Provision for attaching more sensors

The different parts of the robot body are

• Aluminium frame
• Cast steel clamp for attaching motors
• High torque motors
• Custom made nylon wheels
• Battery bay
• Sensor bay
• Provision for circuits
• Provision for surveillance camera

FRAME

The most difficult part of making this robot has been the mechanical frame. The central frame is made from two aluminium bars as shown in the image below. These type of aluminium bars are used for making sliding doors and windows. Holes are drilled to mount motors, circuit boards and sensors.

The Two aluminium rods of length 75 cm have been kept parallel at a distance of 5 cm and attached to the motor clamp.

The aluminium frame is divided into 3 sections. The front section is where the camera head and the obstacle sensor is mounted. The middle section is where the clamp to hold the motors are attached. The rear end has provisions for mounting the battery bay.

BATTERY BAY

The battery bay has to accommodate two 6v,4.5A lead rechargeable batteries. Since it was the end of the frame it was also necessary to implement a universal wheel to reduce friction. I got the universal wheel from a shop that supplied components for refrigerators.

Left: Universal Wheel, Right: Bay Plate

The battery bay was made using a rectangular piece of metal sheet on which holes are drilled to put mounting bolts and also to affix the universal wheel

Battery Bay

MOTOR & CLAMP

FIRE uses two motors, one for each wheel, for locomotion. These are INRAD wiper motors rated at 12V, has 3 speeds of 25, 35 and 45 rpm approx. I got them for Rs.300 each from an automobile market.

The motor should have enough torque to carry the weight the robot and payload if necessary. I found the torque to be 60 Kg Cm. In this robot the motors are made to run at 25 rpm to reduce the current drawn. Peak current drawn is 4 A under full load.

Torque Calculation

Torque = Force x perpendicular Distance

For estimating the torque, we attached to the shaft a steel rod of 10 cm. At the end of this rod weights were added as long as the motor was able to make continuous 360-degree rotations. At a particular weight the motor was no longer able to lift the load. This load was noted to be 6 Kg approximately.

Torque = 6 x 10 Kg cm = 60 Kg Cm

After the robot was made it could lift about 7 kilos. As usual I ran out of more weights. My guess is it can easily carry another 5 kilos. The robot weighs 6 Kgs and apart from all this, I predict it can carry additional 13 Kgs

INRAD 12V ,tri-speed wiper motors

As u can see from the image, if I hold the motors vertically with the shaft parallel to the floor and facing outside, the body of the 2 motors no longer lie in the same plane and causes weight imbalances which will affect straight motion.

Hence a clamp had to be designed with a tilt in the holding area to partially manage the weight imbalance. Though not a perfect design, it still does the job. Better idea would have been to remove the internal gears and custom design new gears .

Motor Clamp rested on a small reddish brown box. The tilt in the holding area is not quite visible

WHEELS

Initial concepts for the wheels were chain sprockets from motor bikes. But they were too heavy and the teeth were dangerous. I decided to make my own nylon wheels for the robot. These have been the most expensive part of the robot. I spent Rs.600 for 2 and half kilos of a nylon cylinder. I took the nylon to a lathe and got the wheels made to dimension.

The diameter of the wheel is 150 mm and width is 10 mm. It has a provision for attaching the motor shaft to the wheel using Allen screws. The diameter of the wheel plays a major role in deciding the speed of the robot.

Nylon Wheels

Linear velocity = angular velocity x circumference

To achieve a speed of 20 cm/min the radius was determined as follows
We know that the motor runs at 25 rpm,

Substituting values,
Linear velocity, 20 = 25 x 2 x pi x R

Therefore, R = 20/(25 x 2 x pi)

On calculation, R = 7.5 cm.

Circuit Board mounts

Circuit boards have been stacked one-over the other at the middle part of the robot using long 8” bolts.

surveillance camera mount

The camera head is mounted on the front part of the robot on the aluminium frame, which gives it a full view of the surroundings.

IR SENSOR BAY

The IR sensors are mounted on pieces of aluminium in the front part of the frame. The bolts enable the sensors to maintain low clearance to easily detect edges.

IR Bay

IMAGES

Motor+Wheel+Clamp

Frame+Motor+Wheel+clamp

The frame with motors , battery bay and camera head mounted