THE DEPT OF MECHANICAL ENGINEERING AND AEROSPACE ENGINEERING

UNIVERSITY AT BUFFALO

MAE 412: Machines and Mechanisms II

Fall 2004 Project Assigned Date: 11 November, 2004

 

Project Description

 

This year’s final group project is to develop a “catapult system” that can be used to throw a squash ball. Final project presentation will be in the form of a competition. The competition will have two parts.

 

A)    Precision shooting

            The squash ball will need to hit a target that could be located at a distance L’. Exact value of L will be an integer between 5 and 20 and will be determined on the day of contest.

 

B)     Maximum range (bonus competition)

      Teams will be awarded bonus points based on the maximum throw distance according to the rules discussed in the maximum range section.

 

Each team will design their own catapult system based on the following requirements:

• The mechanism must use at least a 4-bar (or 5-bar, 6-bar, etc.) mechanism in order to accomplish the task.
• Each team can only use one “standard motor” (as specified below) for powering the system.
• The entire mechanism must be made of wood, and connected together using any means (glue, nail, bolts, etc.).
• The entire mechanism must never leave an operating window of  2’ x 2’ and the operating window must include the entire base plate within the window.
• The mechanism should be mounted on a base plate such that it can be quickly clamped onto a table.
• No part of the mechanism should cross the start plane from where the judges will measure the distance traveled by the squash ball. Any form of pre-stored energy is not allowed before the switch is turned on. i.e. raised weight, stretched spring, chemical reaction, etc.

 

Project Rules

 

The competitions will be organized during the final week of class:

 

• The squash ball can be hand-loaded during the competition.  However, after loading, teams will be permitted only to turn on the switch connecting power to the motor. This means that each valid design must have an automated release mechanism which will disengage the motor during the throw.

 

• The ball must be released within 30 seconds of turning on the motor. The target will be located at a pre-determined location (to be decided on the day of contest) from the start plane. The target in this case is a garbage bin with a diameter of approximately 2 ft (the competition setup is shown in figure below). Each team will get three tries to shoot the ball into the bin. Each successful shot into the bin will fetch the team 5 points. A rematch may be required to settle the decision in case of a tie (which will be solely at discretion of Dr. Krovi)

 

•  It is encouraged to get all parts from student’s houses/apartments/garages, machine shops, scrap yards, etc. Purchases need to be kept minimal, if any.

 

• The specific details of the gearmotor to be used are given below. Please adopt the usual precautions to ensure that you do not burn out the motor since replacement motors may be difficult to procure and expensive.

 

 

• All devices will undergo strict safety inspections prior to the competition. If anyone in the MAE machine shop or Dr. Krovi feels that the mechanism is unsafe, it will not be allowed to compete – no exceptions. All designs that failed to meet the constraints will not be allowed for the competition (the grade of this part will not be given).

 

The total project will be graded based on the following criteria:

• Competition performance (20% of project grade).
• Final prototype - compactness, construction, aesthetics, etc (20% of project grade).
• Virtual Prototype – SolidEdge/Dynamic Designer based analysis and MATLAB based analysis (20% of project grade).
• Written report detailing the design of their mechanism including: (i) the idea generation phase; (ii) motivation behind design; (iii) analysis and synthesis of the mechanism (iv) virtual prototyping of the device; and (v) analysis/discussion of the success of the device (40% of project grade).
• Your final project will only be graded if you successfully create your own model and it works properly during the competition.

 

Further details on the requirements of the Final Project Report will be provided in upcoming weeks. Each member of a group will also submit a peer evaluation form (which will only be seen by Dr. Krovi) and will be used to assess other members’ contribution to the team and its design.

 

 Maximum Range (Bonus competition) 

 

Rules:

• Bonus points will be awarded based on the distance traveled by the squash ball (before touching the ground) during the maximum range competition.
• Each group will be given one chance to shoot the ball the farthest distance using their catapult.
• The maximum distance throw will occur immediately after the three attempts for precision shooting. Hence, any reconfiguration of the mechanism, if required, should be quick and easy. No major reconfigurations (i.e. changes that result in a completely different mechanism than that used for the precision shooting) are allowed.
• Rules concerning time and energy considerations will be the same as those for precision shooting.
• The squash ball must travel at least 20 feet in air (i.e. before first impact on the ground) in order for the group to qualify for bonus points.

 

Bonus Points:

• Points will be awarded on a scale from 12-20 bonus points.
• The group that attains the maximum throw will receive 20 bonus points. Each successive shorter throw will yield one less bonus point.
• Example:

 

 

Project Management

 

Questions about and clarifications of project rules will be managed by a committee of students representing the groups. While some questions WILL NOT be answered, as determined by Dr. Krovi, most of the questions can and will be answered by the committee.

 

Each group will have a representative on the committee who will meet with Dr. Krovi on Friday after the presentations to discuss project objectives and answer project questions. Each such member will have one vote when answers are voted upon. Every question that is answered by this committee will be recorded at the course website. Dr. Krovi however, does have veto power for questions that create unfair or unsafe conditions or those that do not contribute to the requirements or sprit of the competition.

 

Appendix A: Worm Gearbox

 

Use this gearbox for smooth power and lower speeds. Polyacetal gears assure high efficiency and long life. The worm gearbox is a favorite for robotics since the gear ratios available provide excellent torque, speed and holding power when the motor is off. Motor included. Runs on 3 - 4.5 VDC. Assembly required. Please note that the specifications shown below are all that are available. Please note that all available information for this product is shown below.

 Note: This worm gearbox motor is also available for purchase at Hobby Town on Sheridan Drive.

Address: Sheridian Center, 3332 Sheridan Dr.