Offbeat
Engineering
Case Study: Post Driver Manipulator
Problem Definition
Around fifteen years ago Scottish Borders farmer Rob Tinto purchased an
Australian built fence post driver, which was intended to be 3 point linkage
mounted onto a tractor. However he would have preferred it to be mounted on a
trailed chassis allowing all the equipment and materials to be carried on a self
contained unit thus giving the option of only needing one vehicle/operator. Rob
provided us with a disused trailer chassis as a basis for the project.
Our remit was left pretty open, just come up with something to do the job!
Design Considerations – Parallel Motion
In the transport position the driver attachment would have to fold away to at least
within the trailer wheel track and have ample ground clearance. We could have
opted for the usual sliding side shift mechanism as nearly every manufacturer
does. However being
offbeat  we decided to opt for something radically different
with a touch of subtlety,
a parallel motion manipulator with fore/aft
traverse.
This configuration would allow the post to be positioned to anywhere
within a reasonably large
cuboid as defined by the limits of travel of the
mechanism.  Subsequent setting of the post vertical would be affected by a
hydraulic ram in one plane and the post drivers own manual adjustment in the
other. The normally PTO driven post driver would now be powered by a hydraulic
motor.
Brian produced a computer application to simulate and refine the mechanisms
used in this design, and provide us with the principal dimensions.
Commissioning
A local farming friend gave us the opportunity to test the machine prior to delivery to the client. The manipulator arm worked very well
allowing us to access areas which would be difficult or dangerous with a tractor mounted post driver. The post driver did however seem
to require a great deal of effort to work the friction drive mechanism which lifted the hammer weight, that is until the older gentleman
pictured above took control and managed to get the same effect with no more than light hand pressure. So it is true that
older people
are more economical with their effort
, a valuable lesson for we younger generation!!
Fifteen years on – Still going strong
The machine is now 15 years old and still in regular use, being used around the farm as well as for contract work or simply borrowed
by neighbours. The post driver attachment is now looking pretty tired, however the manipulator arm is showing no signs of wear. It
looks like the hydraulic hoses could do with a tidy up though Rob!!
Inspired by this article
Then check out our other case studies, maybe we could help you turn that bright idea into reality. We welcome your feedback whatever
you think.
Fabrication
Making the machine was now a relatively simple process. Most of the hydraulic components were acquired second hand in an attempt
to limit costs. The chassis had to be modified and strengthened to take the fore/aft traverse mechanism and the central cavity was filled
with old kerb stones to give the required counterbalance when the manipulator was fully extended.