A very simple FPV remote control car. I always wanted to build an FPV remote control car since I was kid. Naturally the first thing we made when we got a Raspberry Pi.
We were doing a pitch to Startup Village for the program of teaching kids to make things using Raspberry Pi. We were trying out different ideas on what can the kids make that will get them very excited. This makey was taught to the kids.
Remote control the Raspberry Pi
For remotely controlling the raspberry pi we wrote a simple script that can be executed from the terminal. Keys A, W, S and D control the direction of the car. W moves the car forward, A turns the car left, D turns the car right and S stops the car.
We used L293d as our motor driver. L293d gives up to 600mA of current, which was good enough for driving our motors.
Raspberry Pi power requirements
Raspberry Pi also runs on 5V. So initially we collected it to the supply 5V rail that we created for L293d from the Lipo battery. Raspberry Pi model B requires around 700mA to 1000mA for itself. When we connected the Pi to the Lipo-l293d rail, the 7805 overheated. 7805 is a very lossy device. The drops voltage by burning the rest of the power. So with so much of current drawn and a half of the power wasted at the 7805 the lipo battery lasted less than 5 mins.
Separate power line for Raspberry Pi
Since Lipo-L293d combination is ill suited for Raspberry Pi we looked for an alternate solution. Portable mobile battery was found to be an excellent solution. It gives exact 5V power supply. So 7805 is not required and no power is wasted. We used a 2200mA power bank. So the raspberry pi will run on it for 2-3 hours.
Grounding the 2 supply
Since we are using 2 power source (Lipo and portable battery bank), for the circuits to work properly the grounds of the 2 supplies needs to be connected.
Other parts used
8 volts Lipo used to power the robot
Portable battery used for cell phones.
Nexus 4 was used as the camera. Used an app called Wifi camera - https://play.google.com/store/apps/details?id=teaonly.droideye. Using this app when connected on the network we are able to see the camera field on the browser of another computer. So now we can see what the remote controlled car can see.
Notice that the phone was mounted at the very front of the car. Ours is a 3 wheeled car. 2 powered wheels at the back and one ball castor at the front. Mounting the Nexus at the front changed the weight distribution on the wheels. The castor was taking a lot of load and the rear wheels are not taking enough load. Because the rear wheels was not taking enough load, we were not getting enough traction on the rear wheel. Meaning the rear power wheels were slipping a lot of the time. Since we could not easily shift the camera to the rear we added some more weight at the rear hoping the traction will be enough. This worked. Ideally we should be figuring out a way to distribute weight better.
To move forward - Both left motor and right motor turn on. To turn right, Left motor turn on, right motor turn off. To turn left, left motor turn off and right motor turn on.
5V supply for l293d
To create a 5v supply for L293d we used a 7805. 7805 dropped the battery voltage from 8.8V to 5V for the L293d
Creating a clone of the SD card using mac
Reference used - http://computers.tutsplus.com/articles/how-to-clone-raspberry-pi-sd-cards-using-the-command-line-in-os-x--mac-59911 .
This process is excruciatingly slow. Need to find an alternative.