Duty Cycle:

The approximate duty cycle of the power transmission system was determined to aid the decision of linear thrust supply option. It is assumed that the time between cutting cycles would be an average of 8 seconds. Therefore, if a linear actuator is to be used, it must have a duty cycle rating of 20% or greater.

Linear Thrust Output:

After weighing the options and considering which type of power system would be the most optimum for pruner, it was determined that it would be best to use a Makita XDT08 Impact Driver in conjunction with a linear motion ball screw. Analysis had to be done to determine if the XDT08 unit was capable of supplying sufficient torque to the ball screw to produce the required linear force to the blade system. The majority of the ball screw options which were available would have been appropiate for the application. The chosen ball screw has a diameter of 5/8" and a lead of 13/64"/rev. A smaller diameter ball screw would have been better with regards to weight. However, the chosen ball screw was nearly $80 cheaper than the other available ball screws.

Clevis Pin Sizing:

An analysis was performed in order to determine the minimum diameter of the clevis pin which is to be used to transfer force from the linkages to motor connection. From the analysis, it is determined that minimum diameter the AISI 1020 pin should be to withstand maximum cutting force is 0.152 inches. Therefore, the pins that will be used in the assembly are ¼” in diameter.

Sizing the Driving Rod for Tensile Strength:

An analysis was done to determine the required wall thickness of the aluminum or carbon fiber tube which will be used as the driving rod in the assembly. From the calculation, it is determined that the wall thickness of a carbon fiber tube must be at least 0.0073 inches to withstand the cutting tensile force, 600 lbs. It is also determined that an aluminum tube must have a wall thickness of 0.1495 inches in order to withstand the tensile force.

Driving Rod Buckling Analysis:

The calculation shown below determines that the dimensions established for the driving rod in tension still give the driving rod a buckling load of 2,461 lb. This value is much higher than the rod would ever experience with maximum input torque.