Analysis:

Gear ratios based on using an Andymark Neverest Classic 60 Gearmotor.

We referenced Shigley’s Mechanical Engineering Design to calculate the gear ratios while taking into consideration interference. We came up with three potential gear boxes that gave us a gear ratio of 8, thus a total torque output of 16 N-m for the motor chosen. However, a gear ratio of 8 also means a speed ratio of 1/8, which would reduce the speed of the motor from 105 rpm (no load rpm) to about 13 rpm. We may want to consider trying to find another motor with a similar torque rating, but a slightly higher speed rating.

Bottle Gripping Mechanism

Designs:

This is another potential design for the bottle gripping mechanism. It consists of a set of crank-rocker linkages with grippers that will hold the bottle in place. A few reasons why this design was not chosen were because 1) sizing, 2) timing issue with gripping the bottles, especially if this will require 2 motors, and 3) you’d have to create a third linkage to connect both linkages to one single motor, meaning more parts and space taken up.

This design consists of a set of racks meshing with one pinion. The racks each have one arm that will be attached to them, which will be what holds the bottle in place as the torque is applied to the lid. The arms will have a slight curvature to them to accommodate all bottle diameters and will have a rubber surface to better hold the bottles. So as the motor spins the pinon, the racks will move, causing the arms to grip and hold the bottle in place. Because of the range of bottle diameters, it will be difficult to program the motor to stop on a time basis, therefore the use of a feedback sensor, specifically a force sensor, will be the better option.

Analysis:

Based on using an Andymark Neverest Classic 60 Gearmotor and a 0.021m pinon

We want to determine the force that the arms will exert on the bottle based on the motor choice and if a gearbox will be necessary or whether we’ll need to choose a different motor. We attempted two analysis approaches: an FBD with the forces at play and using Shigley’s as reference. The reason for this is because with the first approach, we have to consider the weight of the pinion/motor to determine the normal force it exerts on the rack, which in turn helps determine the frictional force between them. The discrepancy with this is that the motor will be mounted, thus the weight is distributed to that mounting structure and not from the pinion to the rack. Based on the resulting force from this approach, we would have to increase the torque to achieve a force of 300 N, meaning we would have to add a gearbox with a gear ratio of about 5 to increase the output torque to 10 N. With the second approach, Shigley’s 13-36 depends on the power transmitted and the speed of the pinon. From this approach, we obtained a similar result to the one obtained from the first approach. To obtain a force of 300 N, we would need to use a gearbox with a gear train that would reduce the speed to about 20 rpm, thus a gear ratio of about 5.

Lifting Mechanism

Design and Analysis:

This is the pulley system design for lifting the lid gripping mechanism up and down onto the bottle. The dimensions used are rough estimates based on the sketch model made. Similarly, the weight of the lid gripping mechanism is also an approximation (~ 5 lbs). The system consists of two pulleys, one motor, the rope/cord, and a set of rails to ensure the lid gripping mechanism doesn’t sway back and forth during the lifting process. We want to determine the torque necessary from the motor to lift the lid gripping mechanism up and down. For this analysis, we kept it simply and ignored frictional forces in the pulley system and the rails. From the results, we determined we would need a motor with an output torque of 5 N-m, thus we would need a gearbox with a gear ratio of about 3 if we use the same Andymark motor.