Robotic Sweeper

Objective:

To make a simple wired bot that can carry small paper balls from one place to another.

Approach:

It is always better to make bots in a set of modules which can be assembled together to form the required bot. For the dust bot there are two things required, first a gripper that can hold the balls and second a vehicle that can take that gripper from one place to another. First of all it is required to make a vehicle that can be controlled by the wired controls. After accomplishing this task we need a mechanism to grab the balls. Further the grip of the grabber should be of such strength that the balls don’t fall of the bot till we reach the finishing end. The movement of the gripper should be bidirectional and quite precise as we require the movement of the gripper in both the directions. The stability is the success of every bot. More the stability in your design better is your bot. Hence, the arm holding the gripper should be properly fixed and shouldn’t be unstable. Therefore, aluminum rods were chosen with clamps for enhanced stability of the gripper.  And most important the bot should utilize the off the shelf material and it must be really economic.

The phase-one

For the phase one we require a bot that can move from one place to another. For this simple task geared dc motors will be appropriate. Their direction of rotation is controlled by DPDT switch. DPDT switch change the polarity of the applied voltage and hence the direction of the motor. For more details on DPDT switch the article in insight section is a good reference. After considering the cost factor it is decided to use two motors and a castrol wheel for the bot. This will reduce load on the batteries and also satisfies our requirements. After testing the proper working of the vehicle part of the dust bot it’s time to proceed on the second part i.e. the gripper.

Gripper

The gripper is supposed to be a device that has to pick the balls and keep holding them until the bot reach finishing line. For this purpose a servo motor is very appropriate but it is very expensive. Hence, a very 50-60rpm dc geared motor seems very appropriate. But there is one problem with geared motor. The geared motors don’t stop. After disconnecting the supply they keep on continuing the rotation by virtue of the inertia for a while. Let’s see the troubleshooting.

Troubleshooting

The servo motors are desired because of its precise controlled movement and high torque  but don’t want to handle the troubles associated with it like cost, programming, other peripherals of required to operate it etc. Hence, a clever technique should be developed to acquire those advantages. For obtain the slow speeds and high torque the high torque 60 rpm dc geared motor is sufficient. Now our second problem was to counter the effect of inertia. This is tackled by utilizing “self -locking” phenomenon associated with the dc motor. When we short circuit the terminals of the dc motor it becomes very difficult to move the shaft of the motor. Hence, if we short circuit the terminals of the motor at appropriate time the motor will stop rotating at that moment. This phenomenon can be understood by the “Hopkinson’s test” or can be explained by electrical guy. To obtain the “self-locking” it is required to short circuit the terminals of the motor. Once short circuited the motor will cease to rotate and the effect of the inertia will be countered. See how awareness of a simple phenomenon can save lots of money. To short circuit the terminals a SPDT switch along with the DPDT switch is used. The SPDT switch can be considered to be a tradeoff. But it’s worthy.

After accomplishing this add the aluminum rod at the end of the motor using a coupler. The aluminum rod can be bended at the required angle to hold the balls.

Video:

Control panel

It is very important part of the bot. For controlling motion of the 3 motors there are 3 DPDT switches required. One trade-off “SPDT ” switch is also required. They all are soldered on a zero PCB. Also the controls should be designed in such a way that it resembles the direction of the motion of the bot. In short they must be very simple and user friendly.

 

Image of control panel

Assembling

After carrying out the above two processes almost all the work is accomplished. It’s time to assemble the bot. This is very simple just tight some screws here and there and its finish. The arm of the gripper should be held firm on the vehicle part. To do this the clamps are used for holding the rods to the vehicle, they are tightly screwed to the clamps. To acquire the required angle between ground and aluminum rod, a screw is fixed between the holes of the aluminum rod and the clamp. Further some screws are placed between the aluminum rods to enhance the stability and integrity of the bot. and it’s done.

 

Image showing clamps holding the aluminum rod

 

 

Image showing aluminum rods with screw in between them

Further development

The bot fabricated above is not the ideal one. It may not give the appropriate results. The better model should consist of a servo motor which should be connected to a better gripper with more sophisticated design. Further there should be 4 motors to move it. This will give better torque on uneven path. There can be a better storing mechanism and deploying mechanism. But it’s no doubt that the fabricated bot is very economic and affordable. It doesn’t use expensive materials but utilizes the intelligence.