Can we hack… a radio-controlled car?

Radio-controlled cars, tanks, and ponies have been a staple of children’s play for decades. They enable children to control scale models of real-world vehicles and create motorised play sessions. For parents, radio-controlled toys typically meant batteries… lots of batteries! But in recent years we have seen better-quality radio-controlled vehicles at much cheaper prices. So what can you get for around £30 for consumer-level tech, and how can we hack it? Let’s find out.

General Construction

The Nikko 9018 Velocitrax car is made from a generally firm plastic, with some softer plastic sections typically used to absorb impact. The plastic used is easy to work with, so hacks involving rotary tools, drills, and hand tools are possible.
Measuring approximately 29 cm by 16 cm and 12 cm tall, the car is big enough to easily work with and inside it has plenty of space to add further hacks.

A tank-track-style tread enables the car to cover most terrains. Power comes from the rear wheels, which means that the front wheels are merely there to complete the tracks and provide adequate tension.

Standard crosshead screws hold the shell to the chassis of the car, and only six screws need to be removed in order to gain access to the insides.

Battery Power

Radio-controlled vehicles have come a long way since those early battery-eating monsters! These days we find a 7.2 V Nickel-metal hydride (NiMH) battery rated at 700 mAh. In tests we found that the battery was reporting as 8.1 V after a fresh charge. The battery connects to the car using a bespoke connector that physically prevents reverse polarity connection. The battery is charged by removing it from the car and connecting to the supplied charger unit; charging times are around one hour.

CanIHackItCar

Motors

There are two motors at the rear of the car; these run at 7.9 V and provide both forwards and backwards movement. Each motor comes with three 100 nF ceramic capacitors (104) used to smooth the current flowing to the motors. The motors provide plenty of power for the car; in fact, they are a little too powerful for the size and weight of the car and it is liable to perform wheelies when starting.

When first started, the motors will pull a quick 2.2 A, before settling down to consume around 720 mA, of which the left motor (when looking face to face with the car) pulls 445 mA, whereas the right motor pulls only 285 mA, so this may cause a bias in the steering.

Electronics

Firstly, the soldering for the circuit board is very poor: for the motor connections the solder was barely on the correct part of the board, and there was evidence of the wiring being deformed due to excess heat, so this would be a great candidate for resoldering. That aside, the circuit board is packed with components, but the most important is the X2455 IC that acts as a 2.4 GHz radio receiver and decoder. The X2455 is connected to an antenna and receives radio signals from the controller, which it interprets and then sends the correct response to the two CP2119 H-bridge motor controllers that then rotate the motors in the required direction.

Despite being a common board found in Nikko products, not much is known about the CP2119 motor controller; in fact, the nearest data sheet we could find was for an RZ7889 and this is for a motor controller that works between 3 V and 15 V with a peak output current of 5 A. Should we wish to replace the electronics, then a suitable motor controller would be the L298 series as this can handle up to 4 A of current, but don’t be tempted to use the on-board 5 V regulator to power a Raspberry Pi / Arduino as this is not suitable and could cause issues.

If you haven’t got an L298, then at a push a DRV8833 could be used but this has a peak output of 2 A, so the startup current of the motors means that you are pushing it past its limits. No matter what choice of controller, the existing 7.2 V battery can be reused. Removing the circuit board is simple: it’s held in place by a friction fit and the wires soldered to it. There is plenty of space for an Arduino / Raspberry Pi Zero or other small controller boards and this would make an instant deadly robot!

Radio Controller

Held together with simple clips, the controller is a cheap plastic shell offering two inputs, each with only a forward and backward control option. They are simply covering momentary switches, those that are used on breadboards, and the user merely mushes the plastic of the controller to the button. We see a 2.4 GHz radio transmitter that relays the controls to the X2455 in the car. The controller is powered by three AAA batteries and is a generic unit used across the Nikko range.

Conclusion

The car offers plenty of scope for hacks. It can be quite useful as a donor machine for a Robot Wars / Pi Wars competition thanks to a great battery and space to contain your own electronics. Build quality is decent and there is easy access thanks to using a common type of machine screw. The tank tracks offer stability over many different terrains.

This is a fun platform to hack around with and quite cost-effective when compared to other robot donor candidates.

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