MOUSETRAP VEHICLE 2012 CONSTRUCTION TIPS Bro. Nigel Pratt bronigel@kellenberg.org 1 Dennis Papesh dpapesh@holyangels.cc
Many Thanks Thank you to Bobby B. of Magsig Middle School and Patrick B. of Holy Angels School for allowing us to work with their vehicles. Bobby s two vehicles demonstrate the development of a car over many trials and, perhaps, tribulations. Patrick s car was rebuilt quickly to serve as a demonstration model of a possible two mousetrap car. They gave up some of their secrets to help all teams do better. Thanks guys. 2
The borrowed cars Bobby s 1st Patrick s demo Bobby s 2nd 3
Chassis They come in every size and 4 shape.
Chassis Almost no chassis frame has few, thin members this can help make a very light vehicle. Should increase speed due to lower mass to move. 5
Wide Chassis Wide chasses tend to go straighter. Can add more weight. Might make it harder to stay within the 0.75 meter track 6
Narrow Chassis Very lightweight May be difficult to run a straight line. 7
Chassis A very solid chassis but heavier than needed. Love it, but the chassis can get heavy and the driver and guy riding shotgun look neat but add extra weight. 8
Wheels It takes energy to turn a wheel The greater the mass of the wheel, the more energy it takes to turn it So Use smaller wheels If possible, cut or drill mass out of wheels Especially out near the rim of the wheel Use lighter materials 3 inches or less is good but 9
Wheels Smaller drive wheels = greater speed May spin out on take-off Larger drive wheels = greater distance May be too heavy for decent speed Must balance the two to get the 12 meters if that is the length of the track Remember speed for 0.5 to 8.5 meters, then accuracy 10
Wheels CD size could be a bit large Most of the mass removed to require less energy Front wheels VERY small less mass to move Small wheels all around Single drive wheel reduces energy needed Double wheels up front will keep it straight but require more energy to move 11
Wheels Very small drive and front wheels Low rotational inertia Have to rotate more times to cover given distance Very light chassis Large, heavy wheels add mass and take a lot of energy to turn 12
Wheels CD size can add mass requiring more energy Drilled holes reduce the mass, getting a better effect from the mousetrap s energy Even if smaller CD wheels used, think about removing some mass out near rim. 13
Wheels Most CDs are about 4.5 in in diameter. The CD above is about 3 in in diameter. Think of drag racing vehicles. Larger rear wheels and smaller front wheels. 14
Wheels - Friction The wheels will tend to spin without grabbing floor unless the friction is increased between the wheel and floor. Wheels to left are bare and may not give a good start as they might spin. Wheels to right have something added to increase friction often a stretched balloon. 15
Axle Axle has a ball bearing insert where it passes through chassis to reduce friction. Can be purchased in many sizes from local RC (radio control) stores or hobby shops. 16
OK, so maybe it is just a tidge big and heavy, but it sure is beautiful. 17
Drive Arm Wooden dowel Can be heavy some flex Brass less flex but heavy Aluminum lighter than brass Smaller diameter brass some flex but still a bit of weight 18
Drive Arm All these are using carbon rods sturdy, light, little or no flex 19
Drive Arm Zip-ties May slip Wired and soldered Probably won t slip Tape wrapped May slip a little Is replacement easy and quick??? Like zip-ties, or permanent, soldered. 20
Drive Arm With an easily exchangeable drive arm, students can experiment with the different lengths to see which give the greatest speed but will got the 12 meter distance. Easily cut and replaced. The device above has a larger brass tube attached to the trap but the students can slide different lengths of thinner tube in to test effect of arm lengths. 21
Steering turnbuckle Nut on threaded rod Both of these vehicles have a single unit longitudinal arm frame and seem to aim by slightly bending the frame to one side. 22
Steering Difficult to keep properly aimed. Good way to make small, but lasting changes 23
Lengthen out one or two slots on long arm of chassis right beneath axle attachment. Attach one end of turnbuckle to long arm of chassis and other to axle. Can make minor but lasting changes to angle of travel. 24
Gearing Jump start off the larger axle and then build up speed by switching to a smaller diameter axle. 25
Gearing Somewhat fancier Somewhat simpler, with up to four levels 26
Gearing A simple practice axle to determine the amount of raise you wish to add to the axle and the width of the different levels. 27
Triggering Simple tie-in to trigger both mousetraps at one time. 28
Braking Bobby s 1 st car brake would apply itself on one side of the vehicle and cause a change of direction. Bobby s 2 nd car brake would apply itself in center of vehicle to avoid a pull to one side 29
Braking Small felt pad to absorb some of the shock of braking. Wing nut rides between two rods to eliminate shaking and to help ensure accuracy. 30
String attachment Some students wish the string to come free when the mousetrap has hit home and need to make arrangements to allow the string to slide off. Needs a loop knot at end of string. (find a Boy Scout) Others have enough string on the axle to allow the vehicle to coast without the string coming free. The problem that could occur here is string entanglement which stops the vehicle short. Perhaps a drop of CA glue to keep the zip-tie from slipping. 31
Dowel Rod Somewhere, anywhere, on the chassis, there must be a receiver for a ¼ in dowel rod. The best way seems to be a hole, ¼ in drill bit, in a block of wood which is then attached to the vehicle. This device, while it shows where a receiver might go, does not work well and is for demo only. 32
Get this right!!! The Measurement Point. THE most common reason for problems at inspection. This year, it must be forward of EVERYTHING else, including the wheels!!! 33
More thanks http://www.docfizzix.com/topics/design-basics/mousetrap-cars/ mousetrap-speed-basics.shtml Much of the information on this CD came from here, well, some came from experience All the competitors at the National Tournament at the University of Central Florida whose vehicles, or parts thereof, have appeared in various parts of this presentation. 34
Products Pitsco W24642 35
Products Tamiya - 70098 Patrick used this part to attach axle to the frame. He felt that the frame bed shown above was to heavy to allow good speed. 36
Products Tamiya - 70156 37