Its always fun learning something new. Ever since we got a 2.4 GHz RC system a few years ago, I wanted to understand how these things actually work. How do they send data over the air? What components are used?
Well, in the last months we finally got around digging into it. And it turned out that it is a rather simple affair. So we built our own RC receivers.
The HobbyKing HKR3000 and XR3100 receivers along with two different versions of compatible, home-brew receivers.
In recent years LEDs are appearing on the market that contain a controller chip. Currently the WS2812B is highly popular. It is a RGB LED that contains a simple chip inside. The LED is controlled through a single pin using a serial shift-register-like protocol. Multiple LEDs can be chained together; like a Christmas light.
The WS2812B LED on a breakout-board for convenient mounting.
The WS2812B is an RGB LED with a built-in shift register like controller.
It has 4 pins: GND, Vdd, Data-in and Data-out. With only three wires going
from LED to LED, one can control each LEDs color and brigtness individually.
Using such LEDs makes wiring up a vehicle very easy: one only needs to run 3 wires from one LED to the next.
We are currently evaluating the popular shift-register programmable LEDs of type WS2812B and PL9823 for use in our DIY RC car light controller.
The PL9823 is of particular interest to us as they are in the traditional 5mm dome type LED package and therefore can be installed easily in the light buckets that come with many 1/10 scale RC car body shells.
From a software point of view the PL9823 is compatible with the widely popular WS2812B, with the exception that the data format of the PL9823 is red-green-blue while the WS2812B requires green-red-blue.
The brightness of the PL9823 and the WS2812B seems comparable. However, a downside of the PL9823 is that even if it is not lighting up, it already consumes 7-8mA of current. In comparison, a WS2812B LED consumes less than 1mA when it is off. The 7-8mA is still acceptable for use in an RC car and won't hurt your run time much, but one still needs to take this into account when desiging a system around those LEDs.
The chart below shows the current used by the LEDs when set to white with different brightness values from 0 to 255 on the red, green and blue channels. The PL9823 current usage is ~8mA higher than the WS2812B at every level.
Happy RC-ing!
Most servos and speed controllers come with a wire that is too long for the average RC car. The usual way to deal with this is to either make a spiral by tightly wrapping the wire around a pencil, or by carefully bundling the wire up and securing it with a zip-tie.
A better way, albeit requiring more effort, is to shorten the servo wire to the exact length needed. The unused length of wire is just ballast, and also restricts current flow.
This post shows you how to shorten servo wires.
One type of vehicle that was still missing from our RC fleet was a truck. Tamiya has very nice models; we liked the Globe Liner a lot, but the Mercedes delivery truck would have made more sense for us.
One day we were looking at the offers on eBay and found an old kit from the German manufacturer Robbe. A week later the auction ended and we had the pleasure to win it. Another two weeks went by until we could hold our latest wheeled toy in our hands: