Four-Bar-Lifter Dynamics

Incase its any use to anyone

http://www.micro-maul.co.uk/4_bar_lifter/4_bar.htmlhttp://www.micro-maul.co.uk/4_bar_lifter/4_bar.html

As someone with a 4 bar linkage Im impressed Ewan :)

Why did you decide to write it... too much spare time on your hands :P ?

Ed
http://www.teamstorm.comhttp://www.teamstorm.com

lol, no (er... maybe!).

I had some diagram papers lying around from when I made a four bar lifter last year - and Chris (robotic_ants Chris) was looking for a solution to calculate what torque hed need for his lifter - so I thought Id make a page so I dont have to repeat what Ive said over msn to people over and over again :)

looks very good ewan!

Understandable aswel!

Chris (robotic_ants Chris) was looking for a solution to calculate what torque hed need for his lifter

Doh..! was trying to keep it off the Uk forums..!

Chris - ^_^

lol! I thought that when I realised that you hadnt posted here when I was sticking the link up :blush:

Oh well :crazy: I guess now you can reveal all? :proud:

I second what Grant said. Very good and understandable.

Nice to see that sort of information being posted on the forum. :)

I agree with that, its very clear and understandable even for foreigners like me. :)

Are four bar lifters better than simple single bar flippers when using a pneumatic ram?

I would think so as they dont only push upwards they push forwards at the same time ensuring that you roll your opponent, although with some of the flippers about these days it doesnt matter too much!

The four bar is also a lot stronger as well i have seen some flippers occasionaly break with the amount of force if it is a single lifter however the extra bars give it more strength so it wont break.

SHW Ziggy is doing pretty good with a Nitrogen pneumatics system behind a 4-bar lifter... Selfrights too.

As a side note the US have just produced an excellent SHW HPA flipper using a 4-bar motion by the name of Ziggy its worth checking out...

http://h1.ripway.com/featherweight/Ziggy.jpghttp://h1.ripway.com/featherweight/Ziggy.jpg
http://www.vrogy.com/video/Starhawk3.0_VS_Ziggy.wmvhttp://www.vrogy.com/video/Starhawk3.0_VS_Ziggy.wmv

Chris - ^_^

Are you sure ziggy is a 4bar? It looks like a mortis style lifter, Wereby the back end of the lifter is pulled along in the chassi by supporting rails instead of another bar.
Or is that type of lifter also called a 4bar?

No the front bar is pushed forward by an pneumatic ram the rear bar just follows and defines the angle of lift.

http://h1.ripway.com/featherweight/take_off_every_Zig.jpghttp://h1.ripway.com/featherweight/t..._every_Zig.jpg
http://www.youtube.com/watch?v=n5cgU39pEmshttp://www.youtube.com/watch?v=n5cgU39pEms
http://www.youtube.com/watch?v=cn6KtgcBQ78http://www.youtube.com/watch?v=cn6KtgcBQ78

Chris - ^_^

(Message edited by robotic_ants on April 14, 2006)

(Message edited by robotic_ants on April 14, 2006)

looks good!

No, it looks Great! :)

I say we should abduct Merlin and switch the flipper to a 4-bar system...hehe

Chris - ^_^

Oi! Hands off! Is Ziggy on CO2 or Nitrogen? as although impressive for a 4 bar system, its no more powerfull than most FP bots over here.

The four bar is also a lot stronger

I personally dont think it is, as theres alot more bits to break or bend.

Saying that tho i did consider making an interchangable one for Merlin, as the ram could stay where it was, and just required an extra set of mounting points..

Ziggy runs on HPA, at its last event it was running at 1000psi which I believe produces 3.2ton of force at the ram but it can run at double that 2000psi. Because of the HPA system it uses a fiber wound scuba tank for gas storage.

Chris - ^_^

Ewan, the rear arm length c is important even for initial lifting force calculations whenever b is not equal to b1, because even though the top bar starts horizontal its angle it is not generally fixed.

The formula for the coefficient of lifting force with respect to torque for a frictionless 4-bar linkage infinitesimally above the fully flat position is

(a+(a-c*((a*e/(c*d)-a*e*(d2+c2-b12)/(2*c*d3))1/2-(-a/d+a*(e2+d2-a2)/(2*d3))1/2))*(b-b1)/b1)-1

where d = b1 - c and e = a + b1 - c = base length

This equation does not give valid output when d is exactly equal to zero or if b1 = 0.

One obvious point of conflict with your formula is that when the front and rear bars are of equal length lifting force is *independent* of both b and b1. With your example if the rear bar is one third the length of the front bar the lifting force before friction is now 29kgf...

Anyone ever thought of a wedge shaped 4-bar-lifter?

something like this:

http://members.lycos.nl/rwnl3/technical/td/wapen-schets.jpghttp://members.lycos.nl/rwnl3/techni...pen-schets.jpg

This may be a dumb question but:

Does a 4 bar lifter have to powered by pneumatics?

No it can be powered by anything that can rotate either the front or rear arm, pneumatics are really one of the least popular ways of powering a 4-bar lifter at the moment the more common ones are by a geared down motor or linear actuator.

Chris - ^_^

storm2 is a perfect eample of an electrically powered 4bar lifter. A motor with a worm gear on the end, directly onto the front bar (i think thats how it is anyway)

If only it were that simple! :)
Theres a spur gear stage before *and* after the worm!

Nicks right - Storm IIs lifter is a little more complex than that.

Storm II uses an S28 Magmotor which drives a large worm through a pair EN36 of spur gears to reduce the speed. That worm in turn drives an aluminium-bronze wormwheel which is coupled to a MOD3 small gear which drives the final output quadrant gear to which the front lever arms are attached.

The front axle which carries the lifter arms also drives a 10k pot through a pair of crossed helical gears. The potentiometer provides positional feedback to the speed controller (like a giant servo) and can either be configured to provide end-stop positions or a fully positional servo mode).

Were currently upgrading the arm from an S28-150 to an S28-400 motor and the strength of the gears to prevent them from breaking as weve recently suffered a couple of failures.

The arm moves from its fully down to fully up position in around 0.3 seconds, a speed which will be improved on with the S28-400 which can provide more power, and thus for the same weight we can get more speed and thus thrust.

You can see more details of the arm here http://www.teamstorm.com/heavies/storm2/series7/weaparmour/index.htmhttp://www.teamstorm.com/heavies/sto...mour/index.htm on our website.

Ed
http://www.teamstorm.comhttp://www.teamstorm.com

Re Nick:

I can see that you have compiled a much more accurate equation - which I would no doubt advise those fabricating more costly and complicated systems to use - but my guide so far was much created to provide an easily understandable rough calculation means for the practicle application of four-bar lifters in most given instances. Of course, as you have found, it may not be suitable for some cases.

My second much more complicated equation should give a solution to the problem that you have encountered with my equation. I hope that I can construct an online calculator which will allow people to enter the figures required without any knowledge of the equations behind them to solve their 4-bar requirements. I dont think I shall get round to this until Summer or thereabouts though as Im piled under far too much work at the moment and for much of the forseeable future.

Ewan

Look like someones beaten me to the calculator :wink:

http://www.hyperdynamic.co.uk/4bar.xlshttp://www.hyperdynamic.co.uk/4bar.xls

Way to go mark mellors, brilliant, I shall save a copy

(Message edited by ewan on April 17, 2006)

Here is IO ( now Wazio owned by Chad New ) It makes good use of the 4 bar lifter in a 12 pound robot
http://www.teamcosmos.com/io/build.shtml
http://www.teamcosmos.com/io/1.5/gallery.shtml

(Message edited by aliboy on April 17, 2006)

Its Wedgio - http://www.teamwazio.com/wedgio.htmlhttp://www.teamwazio.com/wedgio.html

Chris - ^_^

lol sorry to go off topic but just looking at a link from that site, I love the fact that typhoon 2 is still ranked number 5 (botrank.com) even though it has been ages since it last faught :)

Wedgio is a really nicely made bot. To be fair to Storm 2, heavyweight lifters are harder in a sense because the stresses required to overcome gravity at their larger scale is roughly double that in a feather.

Has anyone tried a non-flat 4 bar linkage ? I have a picture of what I mean on my profile, it works great in K*bots, the k*bot on the profile has a 13ft flip record with a robot of iits own weight

guess no-one has

not as far as i know dave

Cool, I made it onto the UK forum! :-p Wedgio is now ranked #1 ! ! ! :-) I like the batt 4-bar over the pneu just because of the amount of times that you can use it. Mark only has x amount of pops, I can lift whenever I want + it can also clamp. I still have a few new attachemnts that I have yet to use on Wedgio. Maybe at RoboGames I will have to get some out of the box and take pics for yall.

Hey, sorry to drag up an old thread, but I thought this may be useful:

http://www.totalinsanity.net/tut/mechanical/4barfrontbar.phphttp://www.totalinsanity.net/tut/mec...arfrontbar.php

I made a program that simulates the static conditions of a 4 bar lifter(one powered by the front bar).

I found this thread while I was searching to see if it had already been done, so I thought Id post to let you guys know I finished it.

It plots the start/finish orientations and a torque vs angle plot.

Enjoy!

PS-this only works if you are powering the front bar with a motor... dont try to convert a piston force to a torque, this is a different condition. Im going to be making a new simulator soon for piston powered 4-bars (hopefully itll be a dynamic simulation, so itll tell you how far youll toss the other robot, total time for the lift, etc).

Thanks, Adam. I look forward to your ram powered four bar calc.

Bloody hell Adam - thats a bit good :)

Will be running Storm IIs lifter dymanics through that tonight !

Fantastic bit of VB work too

Ed
http://www.teamstorm.comhttp://www.teamstorm.com