It was brought up
in the comments that what I recognized as a supercapacitor is likely a 1/3 AA size
NiMH battery cell. This actually would make a lot of sense. A
supercapacitor discharges in a way that the voltage will drop
significantly before the energy is depleted, and I did not notice a
significant slowdown in driving speed until the car is mostly
discharged. In addition, the car can run for quite some time before
needing a recharge, and a supercapacitor likely does not have enough
capacity. However, I did not see any charging electronics on the
car’s PCB, which made me think it might be a supercapacitor instead
of a battery, since they can be charged in a much simpler way. That
said, the car charges from the controller, and the charging
electronics could be there. Or, since this device is so cheap and not expected to last long, possibly they are just doing some CV charging of the cell. I'm not very familiar with NiMH cells, but maybe someone else can chime in if such a setup is reasonable for a low cost device. I also previously said the system is charged from a AA battery, but actually the controller uses
2 AAA alkaline batteries.
The below image
shows the top of the controller PCB. A number of components carry over from the car's PCB: the rw1601h and crystal and antenna. The crystal is packaged into a cutout of the PCB, lowering the profile of the setup so it fits in the case cleanly. Four buttons are used for control. The two on the left are forward/reverse, and on the right are for steering. The charging wire is soldered to the board, and runs through the board with some hot glue for strain relief. There is a component near the charge wire that may be a voltage regulator used for CV charging of the NiMH cell?
Because of the battery holder connections in the above photo, the PCB is held into the case and cannot easily be removed to see the back of the PCB. Thankfully, there is a way to get pictures of the rear of the PCB. Another useful tool
for teardowns is the FCC ID lookup tool. By looking up the controller
code (2AJKH-PKRACERC), I could find images of the PCBs inside, as well as a
confirmation that the radio system operates at 2.4GHz. The below image, from the FCC filing, shows that the rear of the PCB is not really used, except for the through hole right-angle power switch.
Partly in support of
another project I am thinking of starting, which would involve
replacing the electronics with my own, I did a teardown of a micro RC
car. This one is a “Pocket Racer” brand car. It is interesting
looking into the design of such a low cost device (whole thing for
These cars are
charged from the controller, which uses AA batteries. In the image
below, you can see that the RC car actually does not have a battery
itself, but rather uses a supercapacitor, mounted in a cutout of the
PCB. This simplifies the charge circuitry, and allows the cars to be
charged quickly. The car is rear-wheel drive, with a single small
motor to drive it. It does not have precise steering control.
Instead, there are only discrete turning options: left, straight, or
right. Interestingly, it appears that the steering and drive are
controlled by H-bridges made of discrete transistors instead of
H-bridge ICs. Presumably this is to lower the cost. It seems the
power for the actuators is straight from the supercapacitor. A small
piece of wire is used as the antenna. Strangely the steering actuator
wires are thin magnet wire. I have not opened up the front of the
case where the steering is, but it is likely that there is a simple
solenoid used to steer the front wheels. On the back of the top PCB,
are two SMD side-view red LEDs, used as reversing lights.
The below image
shows the underside of the PCB. On the front, white SMD side-view
LEDs act as the front lights. The IC is labelled rw1601h, which seems
to be the wireless receiver. I was not able to find details about
this part, but Google returns the 434 MHz RF receiver from SparkFun
as the first search result: https://www.sparkfun.com/products/10532.
Attached to this IC is a can SMD crystal. The power switch is also
mounted on the bottom of the PCB. The charging connector is mounted
next to the switch, with what appears to be a SMD PPTC fuse. On the
other side, there are some power conversion components set up as a
boost conveter: an inductor, capacitor, diode, and transistor. The
transistor gate is connected to the rw1601h IC, so it appears that
component is also handling the power conversion electronics. The
supercapacitor charges up to about 1.4V, so the boost converter
appears to take the lower voltage of the supercapacitor and generate
a 3.3V rail for the electronics.
Overall, it seems it should be pretty easy to replace this PCB with one of my own so I can control this car. I may try running the motor at higher voltage (as others have done to speed them up), and will likely power it using a battery instead of a supercapacitor.