If you are using this circuit I would suggest you reverse the relay connections, ie swap the input & output. Wired like it is if one contact is slower than the other you put a short on the power supply.
Could R2 and C1 be replaced by pots to give controllable variable time delay?
Yes, the arrow through the resistor symbols mean that they are variable resistors with a maximum resistance of their stated value.
Which is all I want to do, in this instance.From looking at the schematic, all this does is reverse the polarity every so often...
I've used one of his shuttles and they work well.Heathcote Electronic Home page
www.heathcote-electronics.co.uk
They have a simple shuttle unit.