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levers, linkages and gearing
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Glen
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levers, linkages and gearing

im just designing this axe mechanism and ive got a bit of a question on how to work out the levarage ratio.

basically the ram attached to the hammer arm 110mm above the pivot/shaft, does that mean the levarage ratio is 11:1 and i multiply the force the ram outputs by 11?

in this case the ram outputs about ~85kg of force, so does that mean there is about 920kg of force applied to the hammer arm effectively? because it doesnt quite sound right.

i think most of my maths is terribly terribly wrong so can someone point me in the right direction Shocked
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Post Mon Jan 17, 2005 11:56 pm 
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Spockie-Tech
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In simple terms, regardless of how the mechanism is constructed, all you need to do is compare the distance travelled by the ram with the distance travelled by the hammer, and take the ratio of them.

So if your ram has a total travel of 100mm and your mechanism turns that into 500mm of travel, then you have a 1:5 ratio, and your effective force at the hammer head will be reduced by 5.

any time you turn a small amount of travel into a large one, force is reduced. when you turn a large amount of travel into a small amount then force is increased.

It gets more complicated after that, with the angles and force vectors having to be taken into account, and then how they vary as the linkage mechanisms travel through their arc's.

For example Mite-E-Er had a problem in that the ram was exerting most of its force trying to push the frame apart when the lid was down, and only really started pushing in the right direction once the lid was all the way up (which is a bit late in a flipper).

Ballistic and Toro you will notice have the ram mounted in such a way that all the force is in the direction of desired travel rather than at 90 degrees to it.

In your case, you would need to take into account the distance from the pivot to the ram attachment point, AND the distance from the pivot to the end-effector (hammer) and work out that ratio.. but its probably just easier to get the ratio of their travel if I havent had a brain-fart here.. Laughing
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Post Tue Jan 18, 2005 12:08 am 
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Glen
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yeah that could make things a tad trickier in that case, might involve some hefty 2 way linkages... i thought it was the other way round but it seems as though ill be getting less than 10kg of force at the shaft in this case..

um lightweight anyone Laughing

thanks anywhos
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Post Tue Jan 18, 2005 12:27 am 
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Woody



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http://www.roboticgladiator.com/tutorials/ax1.html

A little over the top ...but worth plowing thru.

Plus http://homepages.which.net/~paul.hills/AxeWeapons/AxeWeapons.html

Note:- You can use an acceleration linkage 2 speed up the axe during it's stroke.

Post Tue Jan 18, 2005 4:28 am 
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Nick
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Your other option for an axe drive that doesn't suffer from the "Mite-e-er Effect" is to use a rack & pinion drive like The Judge. You attach a beefy pinion gear at the base of your hammer and drive it with a rack attached to the ram. It can be quite low and compact and the leverage is constant. You can get all sorts of gear ratios by changing the size of the pinion gear.
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Post Tue Jan 18, 2005 8:15 pm 
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Glen
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yeah i was thinking about something along those lines, but i thought that an accelerating linkage like woody was speaking of would be better as it speeds up the axe as it travels, as opposed to a constant force along the entire travel, kind of like a speed increasing gearbox i guess.
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Post Tue Jan 18, 2005 9:09 pm 
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Knightrous
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Build a snail cam drive like Beta and use a torqey motor Cool I would have to say, Beta hits better then the Judge and is a good 50kg lighter, using only an Etek for the weapon too Shocked
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Post Tue Jan 18, 2005 10:42 pm 
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Nexus
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quote:
Originally posted by Glen:
yeah i was thinking about something along those lines, but i thought that an accelerating linkage like woody was speaking of would be better as it speeds up the axe as it travels, as opposed to a constant force along the entire travel, kind of like a speed increasing gearbox i guess.


Have a similar idea will try one of these days but Its based on a strong chain and 2 sprockets of diff size so about a 3:1 reduction for the mechanism.
Some sort of cam would make it accelerate and idea am playing with is simply to offset the centre hole in the large sprocket. THat I am guessing might make it do that and lets you try different positions to tune it.

And the chain is used as a link so it doesnt loop around the whole unit. It is actually attached firmly to the large sprocket (holding the axe/hammer) and has something to keep tension on the chain and also holds the slack behind the small sprocket.

Its just a vapour weapon but do have most of the parts.
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Post Tue Jan 18, 2005 11:15 pm 
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Woody



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Yep... beta is an excellent example of the cam system.

http://beta.teamhurtz.com/

Post Wed Jan 19, 2005 6:11 am 
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Totaly_Recycled
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Re spring loaded mech--

Hi Glen ( i had thewrong person in mind so had to edit this bit) That mechanism useing the spring loading device i explained to you can be set up so that the crank angle is off set to the lifter arm angle .

It takes a bit of trial and error but what actualy happens is as the crank rotates from the loaded position to fire . the angles are such that the crank starts pushing at about 2to one ratio .

As the angles between the 3 pivot points shift through their relative arcs ,the ratio increases to 1to 1 then climbs rapidly towards 1to 2 at the end of the stroke .
This gives the lifter or axe arm ect aceleration as well.

The return stroke that tensions the spring is the opposite so as the spring increases in load the gearing ( and the torque required)is reduced .

Different ratios can be set up just by changeing the pivot points but this also affects the length of travel on the arm .
Make a card board mock up of what i explained to you and you will see how it works .

A windscreen wiper motor on 12 volts can easily tension two trampoline springs to a loaded distance of 80 mm which is about as far as they can go with out stretching them over their limit .

I dont know what actual tension load is on them but one spring only just starts to stretch with 13.6 kgs (Vertical limits ) hanging from it .

I have also been thinking of useing the mech to tension a pre presuried ram instead of a spring ..ie a car bonnet gas strutt or similar but i think they also have oil dampening in them so itmight not be a good idea.

Post Wed Jan 19, 2005 11:54 am 
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Glen
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hehe ive got a fair bit of it done out of lexan, at least i hope its the same as the mech you described.

i sent a quick cad of it that i knocked up to your email, its just got the two arms and the pin and pushrod on it, is that how it goes?
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Post Wed Jan 19, 2005 6:13 pm 
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Waddy the phoenix



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in all seriousness i dont under stand that cad what i thought was happening was using a giant version of a chlothes peg spring but it dosnt seem that way i understand slightly how it works but im confuzzeled as to how the it actually streaches the wrong way to fire or am i just not getting it at all?
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Post Wed Jan 19, 2005 9:28 pm 
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Glen
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got a curiousity question,

how do i work out how much linear force (or pushing force) my drill actuator would have? i believe a stock drill has 13Nm of torque so the 9.6v at 12v one should have 16Nm or so. the threaded rod on it is m10 and i just cant think of how you could work out the force it would have...

following up from that how do i work out the force the crusher would have? the point where the actuator attaches is 160mm from the hinge and the hinge is 130mm from the tip of the jaw.

thanks, my general maths seems to be failing me lol
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Post Wed Nov 02, 2005 7:21 pm 
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prong
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hehe, get old scales, put in crusher, crush! read weight!

unless your crusher is too powerful, then if it breaks the scales, dont worry, just use it anyway! Laughing

Post Wed Nov 02, 2005 7:41 pm 
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Knightrous
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IIRC you can just work out how much more gearing the threaded rod adds on and then add that to your gear ratio to find out how much force you produce.
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Post Wed Nov 02, 2005 7:59 pm 
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