This page is to show some more simple to make electronic circuits that are also cheap to make.
One of the main problems with simple relay drive
control is that
the contact faces of the relay frequently burn out.
To put it into simple terms once current is flowing in a circuit
it wants to keep flowing, which is why when you try to open 2 contacts
you get sparks arcing across.
So how can you stop this?
Well one answer I have below is to use a Field Effect Transistor (FET), to switch
the current flow off before you use a change over relay to reverse the motor drive.
As you can see below this can be done simply with the use of a cam wheel
on a standard RC servomotor. The notch in the wheel where the FET switch
locates should have about 10 degrees rotational play to ensure the current flow
will be off when your relay operates and releases.