MAE 412 Machines and Mechanisms 2: Catapult Project 12/13/02

Transcription

1 MAE 1 Machines and Mechanisms : Catapult Poject 1/1/0 Michael Kuczewski Nicholas Laatta Jonathan Leahy Nicholas Leone Kuan Kiong Lim William Louisos Atuo Machuca Jeemy Malik

2 Intoduction: The goup s task was to ceate a catapult system in ode to popel a squash ball the futhest distance. A competition was oganized in ode to compae the pefomance of each goup s design. Each goup was given a set of constaints to follow while geneating thei design: The catapult system must contain at least a -ba mechanism while accomplishing its task. Moe than fou links is allowed, but the mechanism must be at least a -ba. Each goup is also limited to one standadized -.5 VDC electic moto with 16:1 and 6:1 geaing atios in ode to powe the system. The entie mechanism must be made out of wood fo ease of constuction and to pevent an ovewhelming need of assistance in the machining shop. The entie mechanism must opeate within a x x window, including the base plate that it is mounted to. Thoughout the launching pocess, no pat of the mechanism may leave the x x window. The base plate of the mechanism must have substantial oom available such that it can be clamped to a table with two C-clamps. No pat of the mechanism may s the stating plane fom which the distance taveled by the squash ball will be measued. The mechanism may only be touched to tun powe on to the moto and afte the pojectile has been thown. Theefoe, a elease mechanism is needed fo automatic fiing. Puchases ae to be kept to a minimum and all pats should come fom student s houses/apatments/gaages, machine shops, scap yads, etc. The pojectile must be eleased within 0 seconds of powe being tuned on.

3 Fo the pecision shooting potion of the competition, a standadized gabage can would be placed at five-foot incements, specified pio to launch by the goup, and at a minimum of ten feet. Idea Geneation: Afte initially sitting down and discusg the constaints and goal of this poject, we immediately discaded cetain ideas: the use of the moto to diectly dive a link due to its low speed, and the use of a mechanism with moe than bas due to the complexity of constuction and analysis. Then we began to discuss ou options of ug a slide-cank to push the ball o ug a link of a taditional -ba to thow the ball. Initially we uled-out the -ba thowing the ball due to a slightly set back elease point and the potentially inconsistent elease angle and diection. A slide-cank would allow the ball to elease fom the mechanism at the most fowad position of the opeating window, potentially gaining one foot of tavel distance ove thowing the ball. The slidecank would also guaantee that the ball was eleased at a 5-degee angle and taveling diectly fowad. Building off the slide-cank idea, we dew up some sketches fo potential designs. Fo maximum distance, the pojectile would have to be eleased at a 5-degee angle, so we dew a amp extending to opposite cones of the x opeating window. Extending the amp fom cone to cone allows fo the maximum tavel fo the pojectile duing elease, which could potentially allow moe foce to be applied. This was the standad template we used to geneate diffeent designs. Vaiables fo subsequent designs wee: -ba placement, type of enegy stoage, elease mechanisms, and placement of moto attachments. Ou fist design included the input link to be almost the entie length of the base ( feet) and the couple link to be elatively shot. The amp would be constucted such that thee would be an

4 open slot down the cente fo the input and couple links to tavel. A pulley system would be developed to attach the moto to the connection joint between the input and couple link. The idea behind this design was to give the moto the lagest moment-am on the input link, making it easie to stoe enegy. To educe fiction between the slide and the amp, we decided to add wheels o castes to the slide. Fist Design Consideed Figue 1: Slide-Cank with Tosional Sping As fo a type of enegy stoage, we developed seveal types. Ou fist thought was to use a tosional sping at the gound pivot of the input link. The sping would be attached such that it was in its undefomed state when the slide was at the top of the amp. As the moto pulled the input link back towad the base, enegy would be stoed in the sping. When the pulley eleased, the input link would eceive a otational input fom its gound link.

5 The second idea was to use eithe a compession o tension sping attached between the input link and gound. The same idea would apply as it did fo the tosional sping, except the linea spings would apply a linea foce while the tosional sping would apply a otational foce. We decided to discad tosional spings ce they ae not as common and wee less familia to us than linea spings. Figue : Slide-Cank with Linea Spings The thid idea geneated fo this design was to stoe enegy in the fom of a lifted weight. The potential enegy of the weight would be the diving foce of the slide-cank. Fo this configuation, the weight would be diectly connected to the slide, such that two feet of tavel by the weight would esult in two feet of tavel by the slide. The moto would pass though a pulley and also be diectly connected to the weight. A elease mechanism would be developed such that as the weight eached the top of the amp, the line connecting the moto to the weight would be

6 eleased and the weight would dop and popel the slide up the amp. The -ba mechanism in this configuation would mainly seve as a stabilize, keeping the slide moving in Figue : Weight-Diven Slide-Cank a contolled diection. Of these thee designs, the linea sping seemed to be the most pactical, allowing fo diffeent amounts of enegy stoage by ug diffeent types of spings and adjusting thei placement. As the mechanism was constucted, poblems aose with attaching the spings to the input link and wee alleviated by attaching them to the slide and the amp. Theefoe, tension spings wee used to pull the slide fowad and popel the ball. Upon testing, we decided to ty inveting ou design and use the end of the input link to thow the ball and use the slide to move along the base fo contolled movement. This alteation was consideed afte intuitively thinking that one can thow a ball futhe than one can shot-put it. The same tension spings wee used to pull the slide, which in tun, caused the input link to thow the ball. This final design was chosen as it pefomed bette than ou initially constucted design.

7 Figue : Final Design of Slide-Cank Mechanism

8 Constuction: Platfom: As a base fo the catapult ¼ inch plywood was selected because it was easy to cut and povided a solid platfom fo connecting the components of the slide cank. It was cut in a x size so it would be easy to see if the slide cank moved beyond the two-foot window. Link ams: The input cank and couple wee both constucted of ¼ inch plywood and cut to lengths of inches (with an effective link length of 11. inches) and 8 inches espectively. The ends of the links wee ounded ug a jigsaw and holes wee dilled 1 inch apat on the input cank to povide adjustability fo the pecision thowing pat of the competition. The ams wee connected by steel shafts with theaded ends fom which nuts and washes wee attached. The input link was then connected to two wood blocks, which wee attached to the plywood base. Eyehooks wee then attached to each side of the gound link and each side of the couple link. These povided the connection points fo the spings, which supplied the foce fo the thowing am. The squash ball holde was made fom the cap of a spay paint can with the top half of the cap was cut off fo cleaance puposes. It was attached to the end of the input link by unning wie though the cap and hole on the link. Slide: The slide in ou design consisted of two wheels attached to the end of the couple link by a theaded steel shaft, simila to the design used to connect the othe link. Gaphite was put on the shaft to educe fiction between the wheels and the couple link. In fact, this method of lubication

9 was used in all of the link connections because taditional gease does not wok well with wood on metal applications. Release mechanism: The elease mechanism was a elatively simple design. It consisted of a piece of music wie with a cicula loop fom which the sting unning fom the moto was attached. One of the ends was bent into an L-shape, which was placed in a hole at the end of the input link. The othe end, which was completely staight, was designed to hit a block placed nea the moto. The foce fom the impact would push the L-shaped end out of the link, theeby eleag the sting being pulled by the moto. The dawing below illustates the design. End attached to input Sting going to moto Foce fom block Figue 5: Release mechanism design Moto connections: The moto was connected to two sets of two D batteies in paallel configuation and then connected to a thee switch, which could un the moto in fowad o evese. A shaft attached to the geabox acted as the pulley fo ou Kevla sting, which pulled the input cank down, theeby tensioning the spings.

10 Figue 6: Final Design Afte Constuction Please efe to CD fo additional pictues and movies of ou Initial Design and Final Design

11 Analysis equations: Velocity Equation Acceleation Equation Position ) ( m m m j m m m m m C B A The hand analysis equations ae deived in Appendix B. Moe sophisticated testing than would be equied to detemine the exact value of the velocity and acceleation of the slide. Once these values wee estimated, they can be inseted into the deived equations fo a complete position, velocity, acceleation, and foce analysis.

12 Pefomance/Conclusions: With a maximum thow of twenty feet in the distance thowing competition and no tagets hit, ou device was not as successful as we had hoped. Thee wee a few design flaws that became evident as the competition pogessed that could be easily fixed if we had the oppotunity to edesign ou catapult. Ou slide consisted of two wheels attached to one of ou links. Two spings wee connected to the same link as the slide, and the moto was attached to the othe link. We made the mistake of offsetting the foce of the spings and the foce of the moto, caug the slide to vee off to one side if not set up popely. Initially, this poblem was not evident, but with continued testing, fatigue began to take its toll and waped ou link as well as the axle used fo ou wheels. When the slide did not move in a staight line, the catapult had a tendency to not thow as fa as it did in ou initial testing. Ou catapult could be edesigned to have both the sping foce and the moto foce on the same link, and a tack could be constucted fo the wheels to tavel on. This would ensue that the slide moved in a staight line evey time. The cup we used to thow the ball was also a seious design flaw that unfotunately came as a esult of edesigning ou device afte discoveing ou initial slide-cank was unsuccessful. We initially had ceated a cupped aea in the slide of ou initial device fo the ball to be launched fom. In testing, this consistently thew the ball at a 5-degee angle, but ou slide-cank was inconsistent and had a tendency to bind, esulting in thows unde ten feet on a egula basis. Afte ou edesign, we had a poblem devig a cupping device that would consistently thow at a 5-degee angle afte the moto was attached. We eventually had to settle fo a modified cap fom a spay paint can, but this design idea was unsuccessful in competition. Ou low tajectoy thows esulted in thee missed tagets in the accuacy competition, and a deceased thowing distance in the maximum thow competition. In hindsight, we should have constucted a customized cupping device that could have been fastened to the input link to incease stability and esult in moe consistent eleases.

13 Ou elease mechanism could be impoved as well. We used a piece of bent welding od connected to the moto to pull down ou fou ba mechanism. As the elease hit a piece of wood, it was foced off ou launching am, and the catapult would thow the squash ball. This at times esulted in inconsistent thows because the elease had a tendency to not let go of the link smoothly. A moe sophisticated tiggeing mechanism would have esulted in moe consistency fo both the distance and accuacy competition. Duing the competition, we wee pobably too consevative with ou choice of spings to use fo the catapult. We wee concened with how much of a load the moto would be able to pull in the 0-second time limit, and we elected to stay away fom stiffe spings. Since we had a thid moto that we had not used, we pobably should have taken a chance and put ou set of stiffe spings on the device. If the moto was able to pull back the stiffe spings in close to (but ove) the 0-second time limit, we could have always modified ou elease mechanism so that the catapult would elease ealie. The stiffe spings would allow moe enegy to be stoed, and a much geate foce would have been exeted on ou fou-ba, esulting in longe thows. We feel that ou device was successful in satisfying some of the constaints given at the beginning of the competition (time to shoot, size, utilizing the moto, etc.). Howeve, we could have optimized ou design to get bette esults in competition. Had we made most of the changes discussed, ou catapult would have been much moe successful than it was. If we wee pesented with an oppotunity to edesign ou device, all of the above changes would be made and tested to ensue thei success.

14 Design Consideation 1 Appendix A Design Simulations (please efe to disk fo AVI files of each simulation) Figue A-1 - Slide Cank Catapult Slide cank catapult system ug a linea sping and toque engine to impact squash ball. AVI file illustating the dynamic simulation of initial design AVI movie #1. Specifications / Components 1 Input Link Am 1 x 1 x ½ inches Couple Am 8 x 1 x ½ inches Slide x x inches Linea Sping k 8 lbf / inch 5 Toque moto -.N m 6 Gea to Gea atio 1 to 5 (1 inch to 5 inch) 7 Release angle at 5 degees Maximum Thowing Range 1 Maximum Range ug Dynamic Simulation feet

15 Design Consideation Figue A- - Slide cank ug a weight system Slide cank ug a weight and pulley to impact the squash ball. AVI file illustating the dynamic simulation of ou second design AVI movie #. Specifications / Components 1 Input Link Am 15 x 1 x ½ inches Couple Am 6 x 1 x ½ inches Slide x x inches Hanging Mass 0 lbs 5 Toque moto -.N m 6 Pulley - 5 inch diamete 7 Release angle at 5 degees Maximum Thowing Range 1 Maximum Range ug Dynamic Simulation 19 feet

16 Design Consideation Figue A- - Slide cank on tack Slide cank mechanism ug a tack and slide cup to thow a squash ball. AVI file illustating the dynamic simulation of ou thid design AVI movie #. Specifications / Components 1 Input Link Am 18 x 1 x ½ inches Couple Am x 1 x ½ inches Slide x x inches with cup fo squash ball placement Linea Sping () k 0 lbf / inch 5 Toque moto constant angula velocity of degees / sec. Equivalent to 15 second wind up time 6 Released at 5 degees Maximum Thowing Range 1 Maximum Range ug Dynamic Simulation 1 feet

17 Design Consideation Figue A- - Final Design Choice Slide cank utilizing simple sping and toque moto system. AVI file illustating the dynamic simulation of ou final design AVI movie #. Specifications / Components 1 Input Link Am 0 x 1 x ½ inches Couple Am 7 x 1 x ½ inches Two Wheels inch adius Linea Sping k 0lbf / inch 5 Toque moto constant angula velocity of degees / sec. Equivalent to wind up time of 15 seconds 6 Release angle at 75 degees Maximum Thowing Range 1 Maximum Range ug Dynamic Simulation 6 feet