What you can get for $9.00 at Walmart...
If you look around you can find some incredibly inexpensive r/c cars in the toy aisle. This is especially true now as retailers start gearing up for Christmas. On Friday on my way in to UML, I stopped into Walmart and picked up an R/C car for $8.99.
And what do you do with a new toy? You take it apart of course and see what you have...
- Two big wheels that mount directly to two geared DC motors
- Two smaller wheels that are connected to each other on an axle
- A "bonus" fifth wheel
- A really nice 4-AA battery holder
- Motor control electronics that includes two H-bridges constructed out of transistors and diodes
- A remote control (not shown)
- Assorted screws and plastic housings
The two motors have screw holes for mounting and nice long leads which allow them to be easily remounted.
The control board is meant to work with the little remote control but it can also be used to directly control the motors via the Arduino. In this picture you can see the eight transistors that make up the h-bridge. There does not appear to be any protection diodes...
The system is controlled by an IC that is marked as RX-2B. The data sheet for this part refers to it as a "remote controller with 5 functions." The sheet mentions that the pins that control the motor can be activated by connecting them to GND. A little testing shows that there are indeed four pins on the IC that can be used to control the motors. Two pairs of pins that allow each motor to be driven clockwise or counter-clockwise. This is show in the video below.
Once the initial testing was completed it was time to hook the board up to the Arduino. In order to do this it was necessary to solder four leads to the IC and two others to the positive and GND inputs of the control board.
The motors and board are then powered from an external battery supply. At first I used a 4.8 V NiMH battery, during later testing, I connected the leads to a 12 Vdc transformer. The positive lead from the battery is directly connected to the V+ input of the motor control board. The battery ground is connected to both the GND of the motor control board and the Arduino.
The four leads from the IC chip are then connected to four PWM pins on the Arduino board (pins used where 6, 8, 9, 10, 11).
The motors are then controlled using the analogWrite function to both select the pin and set the motor speed. The following two videos provide a description of the set-up and a demonstration of the PWM control of one of the two motors.
