This is my first instructable so i beg for your pardon for any mistake in advance.

Back at my home during my summer vacations, everyone in the house asked me to bring their stuffs from the other rooms. It was ok if the stuff was small or limited in number but most of the time it wasn't.So i thought of designing a mobile unit which i could operate via my phone and let it do the carrying stuff.

Supplies

Arduino uno.
Hc-05 bluetooth module.
2x DC motor upto 3 kg-cm.
2x 60cm diameter wheels.
castor wheel
Batteries
Jumper Wires

Software and apps used :

Arduino IDE
Blynk app

Step 1: The External Structure

I had my writing table at my home and also i arranged some plywood which used for the external framework. The whole structure itself weigh about 3-4kgs but you can use something lighter for the external structure if you want.

To setup the wheels, castor wheels and the study table itself I had to drill holes in my base plywood i drilled the hole approximately 10cm away from the edge. Remember if you are using four wheels instead of two then be sure not to keep large distance between them. Since then the robot will be not able to take a turn properly.

Step 2: Motor and Electronics

The circuit diagram for the same is shown above.

If any problem comes with the direction of motion of motors then interchange the positive and negative terminal of the wire.

If problems comes with the position of the motor that is if you are trying to move left and right operates then interchange the positions of the wire that is from A to B.

Both motors used have a torque of 3 Kg-cm. You can use a more powerful motor if u want if you have a motor driver for it.

I have used a L298n motor driver for these project. I know it can operate only for 3Amps current and both the motor will use more than that limit, but the fact is it can whit stand upto 5Amps because manufacturers show less value than actual. And worst case scenario in these case would be thermal shutdown above 100 degree C.

Step 3: Performance and Miscellaneous

This mobile unit can carry weights upto 7kgs and can move upto speed of 10km/Hr. I have used 12 LiON 2200 mAh battery 4 sets of series arranged in parallel.

The only drawback is its agility. It takes time get enough speed and at low speeds it doesn't develop enough torque to take turn properly. But these issue can be resolved by using light weight materials for frame.

Step 4: Codes and Blynk App

Blynk App

I have used blynk app for the purpose of controlling my robot. The sketch for the same is given below. The robot as you know is controlled via bluetooth. You will get the necessary information on the official website of blynk you need. I have decided to controlled both the motor speed separately but if you want you can control the speed through one controller only. I have also added a button for forced left in the virtual pins 3 and 4. In the case if robot got stuck somewhere and it is needed to change its direction immediately this commands can be used. But these command puts a lot of pressure on the motor drive so better to save it for emergency only. I have also used an Led button, it is a simple button to know whether your bluetooth is connected by your mobile or not. just click that button and if the light near 13th pin of arduino uno blynks accordingly then wola your mobile is connected with HC-05.

The code is given above you have to install arduino IDE and just open it using arduino IDE.