You have been contracted to design the drive system for a mobile platform for Kiwifruit orchards. The platform is designed to hold a bin of kiwifruit, and workers pick fruit from the canopy and drop them directly into the bin.  A suitable motor and power transmission system needs to be detailed to drive the system.

The platform has 2 modes of operation:

1. Picking mode – autonomous speed of ~100 mm/s while workers pick directly into the bin. The machine will operate in this mode approximately 99% of the time it is in operation.
2. Transport mode – manual control of the vehicle at a walking speed of 5 km/hr

The vehicle is expected to drive in typical orchard conditions in Te Puke in New Zealand in the months of March to May on grass, dirt, and mud at slopes up to 8 °.  The maximum weight of the entire machine, including the bin and fruit is 500 kg.  The machine is expected to accelerate to full speed within 3 seconds.

For simplicity, a skid-steering system has been selected in which all four wheels are fixed (i.e. they do not turn to steer the vehicle).  The vehicle is 4WD with one motor per side of the vehicle.  The vehicle turns by driving the left and right sides at different velocities.  The drive system is expected to fit within the bounding box depicted in Figure 1, without interfering with existing components (note: the vehicle is symmetrical).  A link to the CAD model of the vehicle is provided on Moodle.

1. Draw a free-body diagram and determine the power, torque, and speed requirements of the vehicle. You are not expected to consider the turning torque required for skid-steering.
2. Select an appropriate BLDC motor and controller from the brushless motor catalog on Moodle, and an appropriate gearbox from the Apex Dynamics catalog. You may assume the motor manufacturer is able to customize the motor flange and shaft so that it mates with the gearbox.
3. Using the Renold chain designer guide, specify an appropriate chain drive system to transmit the required torque and power to the wheels from the motor/gearbox. Include the number of teeth on the sprockets, size of the chain, shaft center distances, number of links, and lubrication method.
4. Using the ASME shaft design equation, determine a suitable shaft diameter for the four axles.
5. Select appropriate bearings and housings for your shafts from the SKF Y-bearing unit catalog using the SKF rating life equation. The machine is to be run for 8 hours per day, 90 days a year, with a 10-year bearing life.  Use system reliability of 90% and assume an SKF factor of 1.  Assume the bearings are subjected to an axial load of 50% of the calculated radial load.   [10 marks]
6. 2D Drawings
   1. 1. Detail your shafts and produce detailed 2D drawings of your shafts. Use appropriate tolerances and include the detail required to fix the gears/sprockets to the shaft.  Include all information so that the drawings could be given to a machinist, and they could make it to specification without any ambiguity.
      2. Produce a 2D drawing of the assembly. The drawing needs to communicate what parts are needed, and how they are positioned in the vehicle with suitable tolerances where required.  Build upon the existing 3D model which is provided on Moodle.  Include a bill of materials.