Tree Felling Mechanism Cameron Bethwaite, Cid Gilani Zachary Lilley, Joe Stadler and

Mechanical Engineering DepartmentFinal Year Research and Development Project

Project Team 11

Supervisors: Dr Stefanie GutschmidtDr Geoff Rodgers

Sponsor: Dr Richard Parker

Actuation Design:An actuation system was designed to support the chainsaw and drive it into a target tree.- Highly rigid dual ballscrew system carries chain saw.- Mounted in a triple bearing arrangement designed to cope with high thrust loads.- 40W DC motor drive with timing belts for power transfer.- Ballscrew/nut system doubles as a 1:2.5 ratio gearing system.- Allows saw to be driven forward with a maximum force of 1150N!

Cutter Design:A cutting mechanism was developed based on the commercial chainsaw. It has had the following modifications made:- Corner radii increased to reduce lower the acceleration experienced by the chain- Driving sprocket increased in size to deliver higher torque to the chain- A spring activated wedging system for repetitive self resetting direction control of felling - The wedge also eliminates potential blade pinching- A 5kW DC motor to drive the chain at the necessary torque and RPM to easily fell trees- A manual tensioning mechanism to maintain chain tension for multiple operations

Electrical Design:The electrical design was developed to supply power to the two motors and to gather the following information:- Tree diameter, by measuring the stroke length of the gripping actuator- Linear position of the cutting mechanism, using a force sensing resistor strip- Tree motion from the inbuilt force sensors on the blade and wedgeA custom made Arduino board is used for data sampling and motor control of both electric motors

Future Work:It is recommended that the following recommendations for future work are done to improve the prototype: - Investigate a way to operate the wedge for a range of tree diameters and weights- Optimisation analysis into system weights· Optimisation analysis into activation speed, chain speed and cutting reach.

Roller Modification:Rollers on the claws enable the robot to freely move around the tree with a PID system. The advantages of rollers are:- Accurate movement around the tree- Scarf cuts can be made on opposing sides- Precise felling direction

Specifications:The following specifications are for the assembled felling mechanism:- 1/4 scale model prototype- 360 degree rotation around the tree trunk- Max linear force of 1150 N- Max linear speed of 113 m/s with a total travel of 240 mm- Max chain speed of 13.5 m/s- Max operational tree diameter, 160 mm

The InnovationThe New Zealand forestry industry is in urgent need of an innovative product to reduce this industries' high risk of injury. Predominately the felling workers are most at risk. The greatest risks to these workers during felling is being hit by falling trees or other debris. Mechanised felling is considerably safer than manual felling but the machines are limited to slopes less than 25 degrees.Scion have a concept to fell trees mechanically using a remotely operated robot to traverse between trees in the forest. Last year's student team successfully developed a remotely operated robot that achieved scions brief. This year's team was challenged to design a remotely controlled cutting mechanism to be attached to the robot in order to be able to complete the felling cycle.

Bottom view of actuation subassembly. Top view of cutting subassembly.

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