July 2007

101 RADIO CONTROL IN MECCANO

With the prevalence and affordability of modern radio control, almost all Meccano models I build nowadays are radio controlled. There seems to be a few Meccano men around who have tried it, fiddled about, blew up components and experienced extreme frustration trying to make it work. I have written this basic 101 article on connecting up and running a RC Meccano model with the minimum amount of fuss or technicality.

In example 1, I will demonstrate how to wire up a model car for a basic two servo control. One servo physically steering and another turning a switch to reverse and forward for an electric drive motor (no speed control).

In example 2, I will demonstrate how to wire up a model car for a more advanced two servo control. One Servo physically steering and a forward and reverse electronic speed control “Servo” to control an electric drive motor with speed control.

In example 3, I will demonstrate how to wire up a more complex model using all the available channels on the Receiver. In this example, the servos control DPDT (Double Pole, Double Throw) or basic On/Off switches to control individual motors, using a common or individual power source. An Electronic speed controller controls one of the motors as well as powers the receiver and servos.

The Components

Transmitter.

Used to control the model. They come in a basic two channel control up to an eight channel control.

Commonly, all transmitters above four channels will have two paddles controlling four servos incrementally. The other channels above channel four will commonly control the rest of the servos on an on/off or centre off, forward / reverse basis.

Older basic transmitters will only allow a fixed travel on the servos that cannot be adjusted. I.e. fixed travel arc of -90^ to 90^ on servo arm.

More modern Transmitter will allow you to adjust the travel arc of the servo arc using a LED display on the transmitter. Setting the travel arc on servos is important as there is a minimal travel arc required to turn a switch on or off or a defined mechanical movement travel distance needed. It is important to not force the arm of the servo as it will damage the servo motor / shear servo gears. Servos can also be set into reverse throw as well which is handy when setting up and establishing direction of throw needed.

Receiver.

The make and manufacture of your receiver needs to matched to be compatible to your transmitter. The correct frequency crystal will need to be matched to the transmitter and receiver, although newer digital setups no longer require a crystal to a set frequency but can be programmed dynamically.

Transmitters will have the same amount of channels as the transmitter, with an extra power connector.

The servos are plugged into the receiver’s connector to match the channel required on the transmitter. Your owner’s manual will help you match your receivers channel to the required channel on the transmitter or it can be done through trial and error. Make sure to switch off before plugging in or out anything or you will risk blowing components!

Power requirements for the receiver.

The receiver will need to be powered by a typical 6 Volts in order to power the servos and receiver itself. There will be a battery connector on the receiver for this purpose. Consult your owner’s manual if not sure of the power requirements for your receiver. I always use rechargeable batteries for this purpose and would not recommend using DC power for this, I have heard of receivers blowing in this manner. (Time for a Mythbusters special to prove/disprove this)?

If using an Electronic speed controller, the battery connector for the receiver must not be used. The electronic speed controller will have its own power connector and will provide power to the receiver through this. Plug the electronic speed controller into the required servo channel on your receiver and you will see it will power up the receiver and other servos. Don’t ask me how this works, but it just the way it is! Typical voltage input to the Speed controller is 4.8V to 8.4V.

Servos

Servos must be matched to the manufacture of your receiver and your local hobby shop will be able to advise you.

Servos can be obtained in a number of sizes from small, medium (Standard) to large.

I use the small servos to control DPDT and on/off switches. The medium sized (Standard) servos are used for light duty mechanical operations and the larger ones can be used to where the medium size servos fall short. The standard servos can be used to control DPDT and on/off switches where space permits but the smaller sized servos take up very little space.

Powering Meccano motors.

The servo motors are powered by the power supply connected to the receiver or the power supply from the electronic speed controller.

Meccano motors controlled by a DPDT or on/off switches need to be  powered by their own battery pack or DC power.

In the case of a Meccano motor controlled by an electronic speed controller, it will be powered by the batteries plugged into the electronic speed controller. These batteries also power the receiver and servos. Any other Meccano motors controlled by a DPDT or on/off switch need to have their own power supply.

An important note is that most electronic speed controllers will be damaged if they are used to power a motor with no suppression. This is often why Meccano modelers will have a model running fine for a while and will then stop working for no reason. I have never had a failure by merely following this basic rule.

A 104 Micro Farad capacitor (Kondensator) readily available at hobby shops for this specific purpose needs to be connected to the motor in the following manner.

- Solder one of the ends of the capacitor to the case of the motor and the other end to the Positive terminal of the  motor.

- Solder one of the ends of the second capacitor to the case of the motor and the other end to the Negative terminal of the  motor.