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DISCUSSION FORUMS : Forkliftaction.communicate
Forum: Technical arena
Discussion:  Calculate Capacity
Number of messages: 19
START MESSAGE:
richard_s
Kansas, United States 		Newbie here.  Is there any sort of generic capaciity calculator formula(s) or slide rule or progam, to calculate lift truck capacity based on heights, load centers, and fork lengths?  Many thanks for any help.  (If it helps any, we're talking about a Hyster H155XL with a 78" side shift carriage.)

Posted 21 Feb 2007 03:44 AM Reply  Report this message
REPLIES: Sort replies by
sebastian_z
Lodzkie, Poland 		Hello,

Please try link: [url/email removed]-sz.de/produkte-en/resttragkraftberechnung

If it does not work well enoguh you can check other attachements manufacturers like cascade, auramo, kaup ect.



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Sebastian

Posted 21 Feb 2007 09:48 AM Reply  Report this message
InventoryOps
Wisconsin, United States 		There are various simple formulas that have floated around the lift truck community, but I'm still under the impression that you can't accurately calculate this with a simple formula (and you may be asking for trouble if use one of these simple formulas). Unfortunately, I think the only way to do this right is to go to the lift truck manufacturer and have them recalculate the capacity based upon the loads you will be handling (I know this is not always practical).
There was a previous thread on this, I can't post the link but you can replace the thread ID in your browser with the following     trid=675


I will add that the formulas I've seen from the lift truck attachment manufactures (such as mentioned in the previous post) seem to be better than the really simplistic ones I've seen floating around. Cascade has a nice detailed example on their site, but note they also refer you to the lift truck manufacturer for "exact determination".  Their example is focused on calculating the capacity with an attachment, but the concept can be applied to just a different sized load without an attachment.

I have never seen a lift truck manufacturer provide a simple formula for calculating capacity.


Modified 23 Feb 2007 05:28 AM
by poster. 		Reply  Report this message
richard_s
Kansas, United States 		Many thanks for the information and thread; it's good reading.  I finally got hold of the Hyster dealer who gave me a technical brochure for this model with charts for load capacity vs. load center but I'm going to save the info from here for future reference.  Thanks again.

Posted 23 Feb 2007 06:39 AM Reply  Report this message
johnr_j
Georgia, United States 		Richard S.
1.  The lift capacity of a fork lift is determined on a tilt table and tested undr 4 different canditions to mesure fron to back stability - rised and lowered, laterial stability & while traveling and now twith the laod in a side shifted position if greater than 4".  These condtions cannot be readily calculated with a simple formal as there a too many variable liek different manufactures, deflections of the mast when extended, etc. etc. etc

2.  As previously mentioned there are "guesstiamtor" formulas that have been around a long time that are available.  Brudi/Bolozoni/Auroma has one on their web site and you type in the data requested and you get an "indication" of the capacity  but only the lift truck manufactures can give you a relaible answer.  A copy of a competitors capacity charts "ain't" no good for another brand - it is only a "guesstimator"

Like the statement "All Men Are Alike" is a myth fostered by some - all lift trucks are not a like.  It would be a dull world if it was true.

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Have An Exceptional Day!

Posted 23 Feb 2007 10:22 AM Reply  Report this message
richard_s
Kansas, United States 		Thanks johnr_j

What I was actually after and I could have been more clear in my original post, is a de-rate caculation for longer forks and load centers, rather than a "from the ground-up" calculation which is what I think my post probably sounds like.  This Hyster we've got has 96" forks on it, but the name plate says 60" and quotes the capacity at a 24" load center.  We handle generators with it that are about 15 feet long, 6 feet wide, and 8 feet tall.

Anyway I was needing some ammunition to help explain to the boss why the capacity has to de-rate with the physical size of the load, because they just look at the tag and well it says 13850 or whatever and why can't I pick up that much weight regardless of size??

Thanks again and have a great day!

Posted 24 Feb 2007 01:45 AM Reply  Report this message
John_Lambert
Victoria, Australia 		Richard

Lots of good advice above, including johnr-j excellent summary of the ccmplexity of rating forklifts.

I need to add that there are stability standards that forklifts are required to comply with. However marginal compliance with these would result in an unacceptably unstable forklift. So responsible manufacturers rate foaklifts conservatively against the ISO or other stability test limits.

Further forklift suppliers do not indicate which stability requirement sets each rating for a forklift - is it forward stability or side stability? We just don't know.

In regard to your particular problem/ query, you are fortunate because adding weight with the forks down, or increasing the load centre distance with the forks down increases side stability. So you can "safely" ignore side stability issues.

However there is one matter not mentioned above that is critical to your situation and is largely unrecognised. That is the the rated distance of a forklift is both a horizontal in front of the fork face measurement, and a vertical above the fork top surface measurement. So you 24 in load centre is 24 inches in front of the fork face and 24 inches above the top of the forks.

Assuming your generatots are roughly symmetrical in mass distribution, your horizontal load centre is now 36 inches and your vertical load centre is now 48 inches. And both these will increase the likelihood of tipover under braking or when accelerating backwards.

Hyster is one of the few manufacturers who give information of the centre of mass of their forklifts. If you use that information to get the height of the COM unladen it is then possible to calculate the degree to which the forklift capacity should be down graded. To assist you, smaller forklifts will tipover forwards at an average deceleration of about 0.27 g or 2.7 m/sec^2. And hyster may tip at 2.5 m/sec^2

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Better to strive and experience all life’s colours from pain to ecstasy than to exist in a grey life

Posted 25 Feb 2007 02:02 AM Reply  Report this message
johnr_j
Georgia, United States 		Now I am going to get a bit more complicated.:

There is no formula that can be applied  - period. There are situations especailly at higher lift heights that a lift truck can have a lower capacity rating at a 24" load centre  than at a longer load center.    To site an example, a unit with a 240" 4 stage mast.  At a 24" load center the capacity rating is significantly because of lateral stability limits.  But the stability rating improves at a 36" or 48" load center as the combined center of gravity of the machine and load moves awaway from the apex of the stability triangle towards the forward tipping line or triangle base.    In this example  I have seen that  a 4000 lb  unit will ahve a greater rating at a 24" load center than a 6000 lb. unit similarly equipped but maybe more capacity at an extened laod center.
It is the location of the combined center of gravity of machine & load within the stability triangle.   There are just too many "I" be fore "e", except after "c" to be able to "slide rule" calculate this and not expose your selft to liability issues -- sorry.

Most manufactures will provide one rating on the truck nameplate for a lift truck at a low lift height as well as at  the maximum fork height as the operator cannot judge at what point (lift height) when the capacity changes, plus  our "Phladelphia Lawyers" would have more fun if they did.   Most operators do not read the name plate.

To solve you issues contact your local dealer with  make, model, serial number, mast, attachmetns, forks, tire types, etc and ask him what the ratings would be at the various load centers you are looking for.  He can contac teh manufcaturer and get thoe for your - may take a few days.

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Have An Exceptional Day!

Posted 2 Mar 2007 08:12 AM Reply  Report this message
John_Lambert
Victoria, Australia 		More excellent advice from johnr-j

Agree that at higher lift heights things become very complicated - hence my refererence to situations where the load was carried low down.

And because of the height complexity I normaly advise anyone comtemplating lift heights with small forklifts above 4500 - 5000 mm to be very careful and thoroughly assess all the risks.

Hope the advice in total above assists all those facing these issues in their workplace

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Better to strive and experience all life’s colours from pain to ecstasy than to exist in a grey life

Posted 2 Mar 2007 08:50 AM Reply  Report this message
johnr_j
Georgia, United States 		Thanks for youur comments,  John Lambert from "Down Under"!  Say Hi to that Guy with The Big Knife we see in the movies for me if you see him.
Don't want to come a cross as I know it all, but I have 40 years in this lift truck business & if my experiences can help someone stay out of trouble I'm glad to do it.  And with the internet it don't cost "nuttin' "
Once upon a time  I work with a company who disappeared like a rag doll - Allis Chalmers.  We had a young Engineer, name Terry Downing, who work 2 years to develop a computerized capacity calculation system that was so easy to use even sale & marketing folks could use it w/o much training - introduced in 1970.   He first had to gather  physical characteristic of every machine, and data on mast configuaration type & key lift heights, etc. etc.  And every tiem the product engineering group made physical change (of significance) he had to up date the program.   And I learned a lot from him to understand what actually goes into rating a lift - a lot more than simple inch pound calculation - things like limitation of the strength of the tilt cylinders (we all have seen tilt cylinder end caps cracked at the weld for sure), lift cylinder columnary strength, roller bearing limitations (important when lextended load centers are to be encountered),etc, etc, etc.

A Yank In The Atlanta Georgia Area!

JJ

-------------------------
Have An Exceptional Day!

Posted 9 Mar 2007 06:50 AM Reply  Report this message
richard_s
Kansas, United States 		Thanks to all for your replies.  I have learned a lot from this discussion.  The Internet truly is a wonderful tool for this sort of thing.

JJ - funny you should mention Allis-Chalmers; one of the best discussion forums I've run across (besides this one of course!) is [url/email removed].  I used to have a 1950 WD, and now have a 1938 model B and that forum is a great resource for old tractors.  Every now and then someone will ask about a source for parts for the A-C lift trucks.  Kalmar I think is the name I've seen for that.

Posted 9 Mar 2007 07:37 AM Reply  Report this message
richard_s
Kansas, United States 		I was afraid that url in the text might cause problems; not trying to cause trouble on this site!  Just trying to say Allis-Chalmers enthusiasts I've found to be a great bunch of folks - just like you folks on here.

Posted 9 Mar 2007 07:39 AM Reply  Report this message
Jeff
Georgia, United States

 		I started out at a large A/C dealer back in the late 70's - the good ole days as they say.

Anyway, the old Allis-Chalmers and Kalmar AC Parts are available via Tusk Lift Trucks.

Komatsu Forklift USA, Inc purchased the old Kalmar AC, Inc a few years back and Kalmar Sweden put a time limit on the use of the Kalmar name, so it was 're-coined' Tusk Lift Trucks.

You can go to tusklifttrucks dot com to find your local dealer.

Modified 10 Mar 2007 11:45 PM
by poster. 		Reply  Report this message
johnr_j
Georgia, United States 		Jeff from Georgia,
Bet your last name is Winter, Worked for Easter n Lift Truck in PA?

-------------------------
Have An Exceptional Day!

Posted 24 Mar 2007 09:16 AM Reply  Report this message
justinm
New York, United States

 		ok as far as your load center for a 15.500 lb cap truck
to make it simple
youre load is 15 ft long  that is 180" the load center is 90"
your truck is rated at 15500 lbs with no attatchment at a 24"load center
15500 x 24 = 372000 in lbs
you divide 372000 inch lbs by 90" and you get a reduced capacity of 4133 lbs far from your 13580 lb load
add a sideshifter and you reduce that further as it adds weight and increases the load center
30000 lb + machines are rated at a 48" load center
a 30000 lb machine whould have a reduced cap for your load of around 16000 lbs plus much greater lateral stability
again contacting the manufacturer is the best idea as the center of gravity of an individual machine is based on component layout and weight and making sure that the load will not put the center of gravity out of the imaginary "stability pyramid"
also its a great idea for liability protection as you dont want to kill your coworkers based on a bad calculation



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New York, New York its a heluva town ..you know that The Bronx is up ..and im Brooklyn down

Modified 1 Apr 2007 05:09 AM
by poster. 		Reply  Report this message
John_Lambert
Victoria, Australia 		Hi all

Justinm - your advice is far from correct. As I and john-r have indicated the situation is much more complicated.

At the most basic level, with the generator's carried with the top of the forks at 8 in, when fully laden this forklift will tip at a deceleration of about 0.27 g.

In respect to forward tipover, the origin overturning moments under braking are:
Horizontal moments: 15500 x (12 + 8)ins x 0.27 g = 85300 in lb
Vertical moment assuming the distance from the forkface to the drive wheels is 24 in: 15500 x (24 + 24) ins = 744000 in lb
Total overturning moment is 829300 in lb
In revised situation centre of mass in the forward direction is increased to 72 / 2 = 36 in, and centre of mass in the vertical direction is (96/2 +8) = 56 in assuming the generator is carried sideways.
Applying these changed figures gives the following:
Horizontal moments: Capacity x 56 ins x 0.27 g
Vertical moment assuming the distance from the forkface to the drive wheels is 24 in: Capacity x (36 + 24) ins.
Solving these equaltions indicated a capacity of 11000 lb.
Whilst this is still well short of 13580 lb, it is much higher than your estimate.
In part this is because you used a 90 in horizontal load centre (if I apply a 90 in load centre the full calculations give a capacity of 9780 lb still much greater than your calculation).

BUT THIS CALCULATION ONLY APPLIES IN RESPECT OF FORWARD TIPOVER (which is fine if the load is low as the sideways syabilty is increased), AND ONLY APPLIES IF THE FORKLIFT IS BEING USED WITH THE FORKS DOWN. AS SOON AS YOU PROPOSE TO USE THE FORKLIFT WITH THE FORKS RAISED AND THE MAST NOT IN THE VERTICAL POSITION THE CALCULATIONS BECOME MUCH MORE COMPLEX - so as I and john-r advised you need to approach the manufacturer for their advice.

Note that technically and legally you should ensure the load plate is altered to show an additional capacity for this lift and the manufacturer is the best entity to do this.

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Better to strive and experience all life’s colours from pain to ecstasy than to exist in a grey life

Posted 1 Apr 2007 07:53 AM Reply  Report this message
justinm
New York, United States

 		yeah the calcualtions dont seem to go along with a chart for a 7000 kilo mitsu (15500 lb)
at a 1500mm load center (60") it can handle 4000 kilos (8800 or so
so it looks like you might be high on your estimate and im way overkilling it
further showing the need to refer to the manufacturer as we are long time techs and we get it wrong

but

anyway you look at it his truck is too small and could be a potential liability
he should just print this whole thread and give it to his boss as i think we all agree he needs a larger machine

-------------------------
New York, New York its a heluva town ..you know that The Bronx is up ..and im Brooklyn down

Modified 2 Apr 2007 10:43 AM
by poster. 		Reply  Report this message
justinm
New York, United States

 		http  img440 DOT imageshack DOT us/my.php?image=fd70ry0.jpg

here is the load chart edit the link as needed

-------------------------
New York, New York its a heluva town ..you know that The Bronx is up ..and im Brooklyn down

Posted 2 Apr 2007 10:46 AM Reply  Report this message
John_Lambert
Victoria, Australia 		Hi Justinm and others

I understood the forklift was a Hyster.

As I also noted I assumed the generator was carried sideways so the load centre is 48" or 1220 mm and the rating about 4500 kg or 9900 lb.

That aside as I stated my calculations purely relate to operating the forklift with the forks down. They calculate a weight which would maintain the tipover safety margin. And they assume the forks are suited to the task.

The manufacturer's chart must take into consideration operation at full lift height and as noted that needs much more complex analysis both in respect of rollover and tipover. Factors include not only the weight and centre of gravity of the load (and in this case the centre of gravity at full height is much higher than the design centre of gravity) but also the weight and centre of gravity of the forks, carriage and extended mast (information that is not supplied by manufacturers).

Manufacturers are not required to indicate the limiting stability factor at full lift. In your case of the FD70 side stability could be the limiting factor at full height so that any tipover calculation would be irrelevant.

Trust that those who have read this thread and related one's have gained a better understanding of forklift rating issues

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Better to strive and experience all life’s colours from pain to ecstasy than to exist in a grey life

Posted 2 Apr 2007 11:38 AM Reply  Report this message


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