Developing an autonomous
Christmas tree weeder (ACW)


Original Stiga Combi

Stiga stripped of the MMI

Jon working on the electronics

The final ACW in 2004

Testing the ACW. (Note the 'virtual' Christmas trees in the background)

Jon and Jesper testing the ACW in small trees (Note the grey tree guards on the ACW)

Movie of the ACW in action



In May 2002 we started to consider the development of a robot that could control weeds and grasses under small Christmas trees. A feasibility report was commissioned and can be seen at the Miljøstyrelsen website or downloaded here

2003 - 2005

A standard Stiga Combi was bought and stripped of its man-machine interfaces such as the steering wheel, seat and pedal linkages.

All of the actions and forces needed to activate the controls were assessed and suitable actuators bought and fitted under the 'table' (the black frame bolted to the foot panels). The electronics, power supplies and computers were mounted on top of the table and a protective hood fitted to keep it all dry.

The control algorithms were developed in Simulink and downloaded onto the controller running the XPC operating system.

A side cutter was designed to be very light and retract with very little force when in passive mode. The arm was retracted by the controller when in active mode to make sure it did not normally touch the tree.  Note the RTK GPS on the top of the ACW. This was used as the primary source of position information.

The control strategy involved measuring the exact position of each tree, calculating a route plan for the robot to follow and navigating the route while measuring the distance between the cutter and the tree. When the cutter came close to the tree the cutter arm was retracted and the ACW went past the tree and extended the cutter arm again.


This action only cuts those weeds that are in competition with the trees and allows the non-competitive plants to improve the biodiversity within the field and help reduce erosion.

A further report was published in 2005 describing the basic developments and tests of the ACW. It can be found at the Miljøstyrelsen website or here.

A presentation of the ACW can be found here.

Staff involved in the development of the ACW
Henrik Have, Simon Blackmore, Jon Nielsen, Jesper Resting-Jeppesen, Frans Theilby (KVL, Centre of Forestry, Landscape and Planning), Lillie Andersen (DIAS, Horticulture), Erik Anderson (Christmas tree grower)


Young Christmas trees with weeds

Page updated March 2009