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Old 01-26-2009, 11:48 AM   #1
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Default University project.. Spring sprinter...Rc guys for you..

Hello to everyone out there...

I am a mechanical eng. student from the UK and we have been assigned to do a design project..

Almost all my life was deticated in the remote control cars airplanes and helicopters..

Since i was 11 years old i use the forums to help me out with any problems i faced with my vehicles and different other problems..

this time i have a big project to hand in a few weeks time and because i know here there are some open and technical minded people i will ask for your advise and thoughts...


We have been asked to make something to move with a spring fast enough on the floor and be able to go 2m and to have enough power and speed to climp up a hill of 3 degrees for 1m..it must cost about 30 sterling and it must be manufactered in 6 hours time..it must firts be done on autocad and we must calculate all forces and loads...obviously thats my job..

My thought which i think will work, is that i will make something like a pan car with a recoil starter as the spring which will take the place of the motor and i wont make it with suspencion and all that i will just find a was to make a simple front end and a very thin chassis..BUt the mechanisms will be something like a recoil starter giving the driving force to the wheels axle...

What do you rc guys think?
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Old 01-26-2009, 11:57 AM   #2
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If it has to be spring powered, only has to travel 2 meters, or climb a 3 degree slope for 1 meter, a mousetrap car should get the job done. Much less than 6 hours to make one.

Google "mousetrap car" for ideas... you'll find plenty.
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Old 01-26-2009, 12:11 PM   #3
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a mouse trap ? what do you mean how will it work?

I will try and send you my rough drwaing as soon as i finish it..
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Old 01-26-2009, 12:24 PM   #4
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take a spur gear (with OWB inside) with a notch in on an axle on a plastic plate, and put the end of the mousetrap on the notch. let the musetrap go, it will spin the spurgear and start the car. It will then freewheel, and you can put the spur gear in different places to change the power.
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Old 01-26-2009, 01:37 PM   #5
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Originally Posted by didrace View Post
a mouse trap ? what do you mean how will it work?

I will try and send you my rough drwaing as soon as i finish it..
No Google in the UK? The basic mousetrap car has the rear wheels on a solid axle. A string wraps around the axle, then goes to the moustrap. Roll the wheels backwards, this winds the string around the axle, pulling the mousetrap open as you go. When the moustrap is fully open, put the car down and let it go. The mousetrap closes slowly, pulling on the string and turning the axle.

Seriously, Google "mousetrap car" you'll find plenty of pictures, you can even buy kits complete with mousetrap. We carried them in the hobby shop because one of the junior high schools locally did a mousetrap car project every year. The kits we sold used CD discs for the wheels. With the small axle and CD wheels, acceleration wasn't very brisk, but the cars easily ran the length of a pretty big store. We started putting pulleys on the cars to get them to accelerate better... pretty soon we were having mousetrap car drag races...
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Old 01-26-2009, 04:02 PM   #6
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I did a mousetrap car in 8th grade for a project the was very simular. Just get the optimum ratios and obtaining three meters should be an easy task. Heck, i still have the SolidWorks drawings and assemblies for it...

Are there any other rules? Any minimum weight? max spring weight? can it be a rotary spring? Find one of those cheesy childdren cars that "wind up" when you pull the wheels back, those go plenty fast.

Surely this can't be as simple as i'm thinking it is, right?
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Old 01-26-2009, 04:44 PM   #7
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The other requirements is that it has to carry a 500g weight extra and it has to be the fastest of all groups..

i thinks it is difficult to make the drawing... because first you have to design everything on autocad and then manufacture it in 6 hours session..

you can use every sping you want.. coiled horizontal, anything you want but it has to go fast and be safe...

the mousetrap car seems to be a good idea..but i saw some videos and its not fast.. obviously you can make it fast...

my idea would be a good idea if i find a high K spring in a recoil starter which seems a bit difficult...anyone knows of a recoil starter which has strong spring inside?
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Old 01-26-2009, 04:51 PM   #8
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Originally Posted by didrace View Post
The other requirements is that it has to carry a 500g weight extra and it has to be the fastest of all groups..

i thinks it is difficult to make the drawing... because first you have to design everything on autocad and then manufacture it in 6 hours session..

you can use every sping you want.. coiled horizontal, anything you want but it has to go fast and be safe...

the mousetrap car seems to be a good idea..but i saw some videos and its not fast.. obviously you can make it fast...

my idea would be a good idea if i find a high K spring in a recoil starter which seems a bit difficult...anyone knows of a recoil starter which has strong spring inside?
Well damn dude! any spring you want? as you know about the amount of energy availiable, and when that is unlimited, the sky is the limit!!

Are you not profficient in autocad? that may make things a little interesting, but six hours should be enough time.

Do you have CNC machines availiable? or are you gonna have to ghetto-rig the materials and the machining?
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Old 01-26-2009, 05:12 PM   #9
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Most recoil starter springs in the r/c industry barely have enough tension to pull the cord back in... If you're looking to go fast and carry a 500g weight and use a recoil spring, I'd go to a hardware dealer and get a recoil spring for a chainsaw or lawnmower. That'll give you some rip...
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Old 01-26-2009, 05:24 PM   #10
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I think you want to use a torsion coil spring. Mouse traps are equiped with those. But if you need a bigger spring because of the mas, go with a RAT trap.

I made a mouse trap car in highschool years back and my class was able to get up to 25 meters off one release.
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Old 01-26-2009, 05:56 PM   #11
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you want to use a negator constant force spring which... ironically is often called a spring motor... like these... http://www.ametekhunterspring.com/products/constant.cfm .
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Old 01-26-2009, 06:05 PM   #12
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I checked out the mousetrap car. that would be a pretty simple autocad build, but honestly It would be easier to crank out on autodesk inventor or pro-e. I am an autodesk fanboy personally. I would say as far as the design goes after you get a decent sketch you could be plotting the full set of drawings and some exploded views with in an hour and a half.

I would use the mousetrap car as a starting point at and then branch off from there with your own ideas. Maybe a carbon fiber or graphite mousetrap car. remember to use paragon for higher coefficient of friction
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