Thursday, April 8, 2010

I just bought a Mustang

Last weekend I went with members of another ESE350 group to KMart to buy a toy car which we will make RAC (Varun could not make it, but was there in spirit and on phone). We knew there were several specifications that need to be met:

1. the car must be able to move
2. the car must be able to turn
3. the car must be big enough for us to cramp in a couple microcontrollers, sensors, and power supply
4. the car must be sturdy enough to withhold these additional components
4. the car must look slick

Almost every car in the toy department could move in a straight line at the very least, so the first specification was easily met. However we realized to fulfill the second requirement, we would need to actually buy a car that was already RC, because simpler toy cars have no need for the complexity of turning. With two constraints satisfied, we pretty much narrowed ourselves down to the RC car section. All was left to do was to pick a car from the selection looks like it can satisfy the last three specifications. We were prepared to adapt to any shortcoming that our car might have, once we take it apart at home.

I spent more than 20 minutes walking around the store and finally decided on a very nice looking RC Mustang Shelby GT-H, shown in the following pictures. I bought it, and took it home so that I can take it part to see what we are dealing with. (Click to see enlarged).

After taking off the shell, we see the PCB for the original RC capabilities. There are wires connected to the motors and power supply, and we can strip them and integrate/replace them for our own microcontroller. When this PCB was dismounted, we freed up space where we can put the FireFly and the HC12.

The reason why we bought a RC car is so we don't have to make our own steering system, such as with a rack and pinion. As we see here, the RC car came with a very primitive rack-and-pinion steering system where any simple pinion that would fit in the notch (rack) indicated could force the wheels to turn. We can to interface the servo motor directly with this component.

Also, the RC car came with a DC motor, so we could either figure out how duty cycle affects it by testing it on our HC12, or replace with with our own DC motor. The question to be answered here is how we would supply enough current to turn the wheels at a force that can move the car. We had planned to use an H-bridge, but looking at the original DC motor, it seems we might be able to get the wheels spinning without an H-bridge.

As mentioned in our project proposal, we hope to implement a functional lighting system to our RAC Mustang. When I removed the bummer, I saw some very convenient holes where we could loop through some wires; and on the other side of these holes was the clear headlight casing with enough room in between to fit a LED. More modifications would be needed, however, to do the same for the back light.