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knex torsion catapult

Hey guys. i just wanted to know if you guys thought i should build a knex torsion catapult. i havent made it yet, and if i do i'll post a picture of it. cheers, n-striker

Topic by SeMi_AuToMaTic    |  last reply


Is it reasonably possible to build my own torsion springs? Please see details and picture? Answered

the actual coil of the spring could be no larger then 1/2" as it would need to fit in to connecting tubes with an i.d. of just a bit larger then 1/2"  The 2 ends would need to be around 3/4 long, if that makes sense.  It would not need a ton of strength as it would be bent by a small gear motor.  The only catch is that it would be under tension for potentially extended periods of time, 5-10 minutes.  I would be needing around 15 of them, perhaps a few more for any whoops that should occur.  So, if it is a long process it may be easier trying to source out on ebay.  I am on the extreme side of rural so it not simply a trip to the hardware store.  Any ideas would be great, thanks.

Question by iminthebathroom    |  last reply


What kind of rope is best for a ballista? Answered

Would Nylon or Polypropene make a good torsion spring?Or would some kind of metal wire work better? By "better" i mean is able to produce the most force or is able to pack the most force into a 5/8"hole (thats the biggest drill bit i have).

Question by meburnfire    |  last reply


Table Saw Torsion Box

Hi all, I'd like your expert opinions :) I have a hobby size table saw which i'd like to expand. I'm planning to build a torsion box that surrounds the saw top. Do you think a torsion box with a cut out will be sufficiently strong, or will it reduce the torsion box properties too much? I was going to use MDF, would ply be a better option or does it not really matter? Any help is greatly appreciated. P.S. If you have a better idea please say so.

Topic by dimmaz88    |  last reply


Torsion spring resource wanted

I am going to build an arm to hold a tv that will hang from the ceiling. It will be approximately 52" for pivot to CG. As I am a teacher it will be an old fashion heavy CRT (prolly around a 25" tv)rather than cool wazoo light weight flat screen. I am looking for an appropriate torsion spring to take it from hanging to pinned up against the ceiling. I know about garage door springs but can't figure a way to retemper the spring after I cut off a few coils and bend an end so I can use it. Any ideas you may have to come up with a spring (canabalized is fine) or a retempering process would be appreciated! Thanks! Mikey

Topic by Mikey D  


What profile of pole would be torsionally rigid? Answered

Calling all mechanical engineers and physicists. I want to make a pole that can resist twisting forces. The application is a down tube on a bicycle frame. And I want to use bamboo because it's light, very strong, very cheap, and biodegradable. The problem with bamboo is it lacks torsional rigidity because its fibers only run lengthwise. I was thinking of wrapping a bamboo pole with a composite fiber (hemp and glue) at a 45 degree angle like they do with carbon fiber poles but maybe a different shape would be better. Can anyone think of a specific geometry of pole that is tortionally stiff? I noticed some bicycles have a triangular down tube. Maybe if I cut bamboo into three strips and glued them together into a tube with a triangular cross section, this might be less twisty. Am I thinking along the right lines here? My first bamboo bike has a lot of twist and this might be one way to make it stronger. Please let me know what you think. UPDATE: The issue was many fold. The short answer is Tonkin Bamboo is the species to use for bikes. This is what most people seem to use. Also Boo Bikes use dendrocalamus strictus (aka Iron Bamboo). My frame had some cracks possibly due to harvesting at the wrong season. I've recently gained more cracks and the bike flexes even more. It flexes like a noodle but I can still do an endo no problem. Go figure. Also hemp sounds like it gets more stretchy after being flexed about 1000 times whereas carbon fiber stays stiff. And squishy wood glue is probably not as stiff as epoxy. All this adds up to a flexy frame. My next one will be tonkin bamboo but I will try hemp and non-toxic wood glue again. UPDATE #2: I'm making a three wheeler and my engineering design teacher gave me some advice involving spaceframes and triangles. The plan thus far looks like this upright tadpole trike: UPDATE #3: I think I've got it! Instructables sent me a box of K'nex and I built up a model of a standard bike's frame. The thing is, when a bike frame twists, the opposing corners of the trapezoidal shape come closer or further apart. So a deep X brace from corner to corner seems to fix most of the problem. I'll try to post a youtube vid of what I mean soon.

Question by snotty    |  last reply


What fun stuff can we do with a garage door torsion spring? Answered

Recently, I received a 10 foot section of new overhead door garage door torsion spring. It looks like the picture below (but mine is spring only - does not have the mounts on the ends). What fun stuff can we do with this spring? 

Question by bobzjr    |  last reply


How Can I Improve My Catapult? Answered

So I built a mangonel (torsion catapult) for science olympiad, and it must launch a foam ball up to 15 meters. But, its struggling to reach 10 meters. I was wondering how I can make it launch further, whether changing the tension of the torsion bundle, different rope, or even structural changes. I will gladly accept any and all suggestions.

Question by sean_sylvester1    |  last reply


Will a torsion spring work with this broom/mop holder? Answered

I am in the late stages of working on a broom/mop holder.  The engineering is not original, however, I may be able to show how to make it fast and cheap!  The function of the device centers on a Cam which rotates up or down and then automatically returns to a "home position". As you slide a broom handle into the cam, the cam gently opens up and accomodates the handle.  But when you pull down or let the broom go, the cam rotates downward and holds the broom very steady.  To remove broom, just push it upward a bit... The design I currently have is using elastic - but I believe we could employ a torsion spring instead. Would using a torsion spring work? How would it work or be positioned on the device? Can I make a torsion spring?  (i'd really like to do this) Can I buy them at reasonable prices anywhere? I have included a few pictures to illustrate the question... Note:  I did later figure out how to properly spell "TORSION" Included is a shot of some example springs. Also in one of the shots, I attached the mechanism to a clear plastic OJ bottle. (thought it might be easier to see the mechanics this way) Thank you for any input you may have!

Question by bobzjr    |  last reply


Giant Spring Replica (How-to?)

I'm working on a Halloween prop (though, with what little time I already have, it looks as if I will have to use it next year), a part of which is supposed to be a metal torsion spring. I am at a loss for ideas that would look real. I suppose whatever it is, I could paint it silver. Any help would be appreciated!

Topic by Bran    |  last reply


Soldering copper question.

I'm working on a project that requires soldering a 1/4" OD copper tube into a hole drilled in the side of a 2" copper pipe. Will a soldered join (not brazed) be sturdy or do I need to do something to reinforce (cut threads into the tube and pipe, flare the tube and insert from inside, etc) it? There won't be a lot of stress on the join but there will be a small tap on the tube to there may be a bit of torsion now and again. Thanks for your responses!

Topic by Mr. E Meat    |  last reply


Strong coil spring

Hi, I want to build a rotating mechanism powered by a spring. Once released,I need the piece to make 2 rotations in a fraction of a second. I also need it to be quite powerful since it will have to push another piece. For this application, I believe that a coil spring (such as those we can find in clocks) is the best suited, but will it be powerful enough ? An if I use a torsion bar spring, the problem is that I probably won't find one that can make 2 turns.... they are usually designed to be used on small angles only. I would be glad to have your advices ! :)

Topic by 1tibo2.    |  last reply


From Concept To Product

So the frame is 95% done -- the last bits are: 1. Fit into fairing (that top tube thing will be cut down significantly) 2. Powder Coat 3. Debug (we have more torsional flex than we want) But, it's a LOT of fun. You're butt is 7 inches off the ground. You can cruise at a pretty fast speed with relatively little effort (compared to an upright bike). And it is VERY comfortable. Just showing something coming up -- a video on this has been encoding since 11:30 last night, and it says it has 403 minutes remaining :P Feedback?

Topic by trebuchet03    |  last reply


anyone have an idea for a good knex solid axle suspension?

K so i have ideas for everything else, can someone come up with a good solid axle suspension for a rock crawler out of knex, i also came up with a torsion bar ifs set up...if you can make a SMALL cv shaft i could make 4wd steering and indipendant as well, but for now i want solid axle! lol i just want to see how many ppl can do all this, steering idea would be good too!

Question by aaronj    |  last reply


My REAL catapult

I recently built a Huge catapult at my friends house out of old decking. It is 13 feet long with a 14 foot arm. My friend needs to get the drill fixed so we can finish and until then we are waiting anxiously. It should shoot a large, 10 pound rock about 100 feet. The next time I go over I'm gonna bring my camera and take a video of it, and guess what? It's powered 100% by torsion just like the Romans. It uses 2 inch diameter rope. I also made a Roman Scorpion which uses 1 inch diameter rope and shoots large arrows 100 feet.

Topic by Electroinnovation    |  last reply


K'Nex sniper rifle contest!!!

K'Nex sniper rifle contest!!!the first contest for this group. this contest is not intended to give people time to make a sniper rifle now, but already have a sniper rifle made AND posted. all you have to do to enter is to put your instructable in the group. this saturday i will make another forum with a list of the entrants. then the voting will begin. so to enter you1. have to have a sniper rifle2. have a insructable for it.thats it.3. it has to be made out of knex only, they can be modified as broken but not melted down to make a barrel or anything like that.4. it can only use compression(string) torsion(string twisted) and tension(rubberbands), no air compression allowed.so good luck to everyone!for inspiration, i will put a picture of my newest creation, MY SNIPER RIFLE! it is finished and i will post a instructable soon.(i won't enter it into the contest though)

Topic by dsman195276    |  last reply


Lockpicking, anyone?

Why the tools section? Because it's a tool for me and not for you (joke joke of course it's a tool for you). I am trying out lockpicking since recently but I am having difficulties. First off, my pick sucks like hell. I can't just go out and buy a hacksaw blade and file it down accordingly. Second, I can't find a suitable torsion wrench for my handiwork. Third, I am trying out the single-pin technique, and that involves feeling all the individual pins to know which is the binding pin, which I can't feel in the first place because my pick is too thick for the lock.  Any idea how to: Make a DIY pick Make a tension wrench without sacrificing my precious tools Feel those annoying to reach pins (Must not involve paper clips in any way imaginable) Yes, I am aware of raking/scrubbing and that all too useful snap gun. Which reminds me also how to make a snap gun without those window wiper inserts or paper clips (tried paper clips already).  Heads up on my economy: I have no bench grinders, angle grinders, or any other power tools available. I either have to do it manually with hammers, pliers, or files, or I have to make my own tools, which usually fail miserably. I have stuff that's sitting around here like a tank of acetylene (I don't know if it still is pressurized or not, either way I don't want to know), some copper pipes (don't make me file those down), a few C-clamps, random soldering equipment, and limited access to the hardware store which my mom owns (limited being no power tools or major stuff I couldn't even use like sheet metal, fiberglass and other stuff). In case you're wondering, that door to my bedroom is somehow always locked and I couldn't get in, hence my motivation to pick my way into the room.

Question by nutsandbolts_64    |  last reply


Cleaning House....by house I mean machine shop

Ok...finally compiled a list of everything that's going so I don't have to make multiple posts... this is it:Water Heater 10 gal. Electric 22x24" $100CRT Monitors Qty. 4 FreeToledo Scale Vintage Counting Scale $100Electrical Boxes Various sizes, shapes $10eaDayton Right Angle Motors (Davit motors) qty2 (L&R;) 1/35hp from a boat model 5K5355 RPM 1725 $300 for both or $200eaExtrusion Various sizes, shapes, qty. $1/lbCable winch from boat trailer $20Time Clocks Mechanical, broken $20 for bothBrewmatic Junior Industrial Coffee Pot $60Baseboard Heater $15Matsuura tool holders *NEW* (qty2) setting/changing fixtures fits BT40 $470 for both or $275ea2 Spring Testers 1 torsion $Price unknown at this time1BridgePort DRO +Scales Scales OK, DRO broken $100Mitutoyo Touch Signal Probe 192-001 $115Micrometers Mitutoyo 8-9" part# 103-223 $125 & 10-11" part# 103-225 $135 or $200 for bothGarnet Hopper Jet Edge new this runs $8700! $800Spring Wire Various sizes, stainless (17-7, 302) and music wire $1/lb - large coils (pm/email for list)Drill Sharpener Darex M4 w/ accessories $500Drill Sharpener SRD 80-M $400Garmin GPS Old, still works! $10Briggs & Stratton Motor NEW. 18hp cast iron, twin cyl. 964cc $999Metal Desk 60" wide, seafoam green metal $60Hose Clamps 5.25" in diameter $.25/eaCoffing Hoist 1/2 Ton 3 phase hoist. Works, but is dirty. Has controls $450Pepsi Machines 2 older can machines. They work & we have keys $100Lip Cutter/Grinder Alexander 2CG (for engraving tools)w/accessories $600Capacitance Meter Emco Capacitance Meter, old, good condition. $20All prices are obo. It can be shipped UPS (sometimes USPS). I have pictures for most of the things on the list.Email garagesale@pittraffic.com if you are interested. I don't check PMs very often, but PMs ok too!THANKS!

Topic by Rainbowlaces    |  last reply