Pulley size, RPM, HP calculator??

[tinkerer]

Anyone know of a good HP, RPM calculator to find recommended pulley size?
Thanks!
Ben

[luv2weld]

Try this page.

http://www.utterpower.com/conversions/

Ralph

[Ronmar]

What are you trying to do?  There is no real HP-RPM calculator that I am aware of.  If talking about an engine, HP is typically a factor of the engine RPM.  That HP whatever it is, will be transfered across whatever pully ratio you select minus of course the friction losses involvd in the belt/pully mechanism.  Like in the link Ralph mentioned, if you know your desired engine RPM and the desired secondary RPM, divide one into the other.  Your pully relationship needs to maintain this same relationship.  I will use my 6/1 genset as an example.  I have a 650 RPM engine and need 1800 RPM at the generator.  1800 divided by 650 = a 2.769:1 ratio.  So if I have a 24" primary pully, I divide that by 2.769 and arrive at a 8.66" secondary pully at the generator.  With 650 RPM on the 24" pully, I get 1800 RPM at the 8.66" generator pully... 

[tinkerer]

What are you trying to do?  There is no real HP-RPM calculator that I am aware of.  If talking about an engine, HP is typically a factor of the engine RPM.  That HP whatever it is, will be transfered across whatever pully ratio you select minus of course the friction losses involvd in the belt/pully mechanism.  Like in the link Ralph mentioned, if you know your desired engine RPM and the desired secondary RPM, divide one into the other.  Your pully relationship needs to maintain this same relationship.  I will use my 6/1 genset as an example.  I have a 650 RPM engine and need 1800 RPM at the generator.  1800 divided by 650 = a 2.769:1 ratio.  So if I have a 24" primary pully, I divide that by 2.769 and arrive at a 8.66" secondary pully at the generator.  With 650 RPM on the 24" pully, I get 1800 RPM at the 8.66" generator pully... 

I can figure out the ratio I need to get the RPM i want, but more importantly, how big do my pulleys need to be to be able to transfer the power without slipping based on what HP my engine is running and what RPM.

[Ronmar]

I understand.  Perhaps a belt manufacturer such as Gates has an application tool on their website, and can suggest a belt for a particular HP RPM combination...

Again, what are some of your specifics.  This may be something someone here has already done, or have some similar experience to reccomend a particular belt/pully combination that will deal with the HP you are working with.

[Tom Reed]

To do that look at the specs for the belts you intend to use.

[Frank S]

Look up Martin Sprocket & gear and download their catalog it has just about everything there is to know about mechanical power transmission designs charts / graphs sizing engineering technical data. a must for any designer / engineer or gear-head who uses belts, chains, bearings, or gears, in their work. 10 times faster than my mechanical engineer's reference book11th edition

[sailawayrb]

If you desire, I could build a JavaScript calculator pretty easily/quickly to do this.  I already have all the equations in the Cross Flow Turbine spreadsheet I posted several months ago.  

http://www.microcogen.info/index.php?topic=2288.0

You typically start with the known HP, known input RPM, known input pulley pitch diameter, known input/output pulley center-to-center distance, belt coefficient of friction (which is dependent and known for each style of pulley/belt) and your desired output RPM.  

Then you can calculate the drive ratio, output pulley pitch diameter, input pulley belt lap angle, output pulley belt lap angle (the lap angles and the friction are required to calculate the required static belt tension to ensure that slipage will NOT occur), belt length, belt velocity, belt tension ratio, minimum dynamic belt tension, maximum dynamic belt tension, required static belt tension, static pulley bearing load, dynamic belt tension, dynamic pulley bearing load and finally, the output shaft torque.  

Of course, if you know the RPM and the torque, you can calculate the power (HP or KW).  The power does NOT change across a drive system...only the RPMs and torques change (assuming the drive system friction heat losses are insignificant).  

Bob B.

[sailawayrb]

Okay, I built and attached the JavaScript calculator needed to properly solve this problem.  

Download the attached "Pulley Drive System Calculator.txt" file.  Change the ".txt" extension to ".html"  Then double click the "Pulley Drive System Calculator.html" file.  It should then open up in whatever browser you use (e.g., IE, Mozilla, etc.)  

Enter your input parameters (HP, Input Pulley Speed, Desired Output Pulley Speed, Input Pulley Pitch Diameter, Pulley Center-to-Center Distance and Belt Coefficient of Friction) and then hit the solve button.

You will probably get more output parameters than you really care to know.  The ones you likely mostly want are the Output Pulley Pitch Diameter, Belt Length, Required Static Belt Tension, and the Output Pulley Torque.

Please feel free to check my math as I only had 10 minutes this morning to build it.

Bob B.

[Tom Reed]

Very nice calculator! Now for us really lazy people it needs a table of belt info so we can select a belt type and see how well the calc compares with the belts operational specs. 

Oh and just a small suggestion, the pulley center to center was a bit confusing at first, perhaps shaft center to center might be a little more understandable.

[sailawayrb]

Thanks Tom. Yes, please keep the suggestions coming and I'll update it in a couple days and likely put it on my website with the other calculators.

I would be interested in hearing how well the calculator results compare to belt manufacturer operational specs. I believe as long as you work in pitch diameter and select a friction coefficient consistent with the belt type, it should provide fairly good results.  This link provides some guidance on what to use for the friction coefficient:

http://metalab.uniten.edu.my/~kamal/documents/Machine%20Design%20Lab/Laboratory%20Manual/Belt%20Drive%20Experiment.pdf

I have become quite a fan of JavaScript. It only took a Sunday afternoon to gain a decent working knowledge of the programming. It also has many features that I believe make it preferable to Excel for doing these sort of calculations. The only downside is that the data is not persistent...you have to write down your final solution on paper in order to retain it  

Bob B.

[Tom Reed]

Ah yes life in the sandbox of Java.

[sailawayrb]

Updated with Tom's suggestion and updated so it will now also handle both flat and vee belts.  Please see my previous posts for the specifics relative to downloading and using it.

Bob B.

[Henry W]

Here is one. http://blocklayer.mobi/pulley-belteng.aspx

A simple one that anybody can use.

Henry

[sailawayrb]

If you only need to calculate the pulley diameters to achieve your desired RPM, that simple one will do the job (assuming you work in pitch diameter).  However, if you want to make sure you can transmit your HP without belt slippage and you want to know what the minimum initial belt tension must be to accomplish this (along with the resulting static/dynamic bearing loads so you can properly select bearings), then you will want to use the calculator I posted.  BTW, you will notice that bearing loads are lower when the pulley drive system is actually operating, this is indeed the reality.

Bob B.