This little project started out at trying to duplicate commercial
chainlink fences that slide open.  After that I started thinking
about making it open under power.  After musing at lunch time
about how I should have taken an old garage door opener when I
 moved from my house rather than leaving it for parts my foreman
 offers me an old one that had its electronics go.
The drive chain is simply half inch pitch bicycle chain with
several master links to make the distance.  I had the forsight
to imbed a five foot piece of 12 inch channel in the concrete
curb under my chainlink fence.  I could in effect weld to the 
curb rather than drilling the concrete.
Bits and pieces of angle and plate standing vertical
provided a bolting surface for the motor. To allow the
single sproket to wind the chain back and forth I created a Zee drive.
The chain goes over the drive sprocket then down and around almost
180 degrees over a stub shaft with two sealed single row ball bearings.
The two bearing act as a pulley to reverse the direction and lead
it to the other end of the gate.
I also had installed an outside plug on the corner of my garage
with a GFI. The button box at the top of the gate is going to have
a key lock to turn off power.
One thing that could be improved.  I should have set the motor higher.
With sag of the chain it almost touches the ground.
The other caveat:  There are no safety devices on this gate so 
caution is required when it is operated.  That is why there is a key lock
and this is a household that has no children.  The buttons will only 
operate the gate while pressed creating a sort of deadman's device.