wheel turning torque calculation.
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Posted by: korena ® 05/22/2009, 03:29:43 Author Profile eMail author Edit

Im trying to design a wheel that is supposed to rotate a balanced system (wheel is pinned to the body of the system, and will not turn unless force is applied) ... the problem Im having is that the system is very heavy(70kg) but the torque calculation results in an extremely small torque required to rotate the system at specified rotational speed and acceleration. assumptions: the load of the system is considered a force applied on the wheel,so, the inertia of the system is not considered in torque calculations. Balancing : static balancing is applied, counter weight is added to the wheel to balance the forces acting on the wheel,hence, no rotation will occur without applying force. calculations and problem details : w = 0.05 (rad/s) a = 0.025 (rad/s^2) r = 0.25 (m) (wheel radius) m = 20 (kg) (wheel mass) I = 0.5*m.(r^2) (kg.m^2) T = I(kg.m^2). a(rad/s^2) (torque required) = 0.625*0.025 = 0.015625 N.m -------> (too small I think) a simple representation is attached. Any thoughts ?

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: wheel turning torque calculation.
: wheel turning torque calculation. -- korena	Post Reply	Top of thread	Engineering Forum

Posted by: thebigcance ® 05/26/2009, 11:53:56 Author Profile eMail author Edit

i got two documents regarding bearing selection and got to skf website, u can register for free, and do the bearcing calculation there............userfrdly site.............the documents i have cannot be sent here, if u wish to give ur email id, i will send it throu.............

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: wheel turning torque calculation.
: wheel turning torque calculation. -- korena	Post Reply	Top of thread	Engineering Forum

Posted by: thebigcance ® 05/22/2009, 03:50:56 Author Profile eMail author Edit

normally a shaft carrying such heavy loads is subject to heavy initial torque....and u have two loads on either side, it doesnt matter if it is in grmas, but if it is in kgs, the bodies tend to run outside the path of the wheel due to centrfugal force, so the shaft should be strong enough to minimise that......and torque is inversely proportional to rated rpm........mount the shaft with the wheel on two unit bearings and give an indirect drive, like the wheel connected to a shaft and driven by belt drive.........put a variable frewquency drive, which will safegaurd the shaft and the 2 weights it is carrying equally..........becoz a direct drive is not prferable in cases of heavier loads........any unbalancing caused after a while will allow u to change the bearings, or the belts from time to time.........this is the advantage of a belt drive........... thnx and regards, ram

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: : wheel turning torque calculation. -- thebigcance	Post Reply	Top of thread	Engineering Forum

Posted by: korena ® 05/24/2009, 23:31:20 Author Profile eMail author Edit

Thank u very much for your contribution, I will definitely take the centrifugal force into account, note that the bearing friction is neglected in calculation, which is one of the important forces assumed 0 for ease of calculation ... I will come back to them for sure, but dont you think the rotational speed is too low for centrfugal force to build up significantly ? ... I mean Im talking about 1 rpm with an acceleration of 0.025 Rad/s ... just a thought ... thnx, korena

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Posted by: jboggs ® 05/25/2009, 11:42:04 Author Profile eMail author Edit

A few thoughts: If you ignore friction, then the only torque required will bo to overcome inertia. I haven't checked your math or your units, but small mass plus, small acceleration, plus small diameter = small torque. On the other hand, I think system friction is probably your greatest factor, not your least. You didn't mention if yoru rotation axis is horizontal or vertical and what your bearing arrangement is. These are critical factors that significantly affect the system friction.

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Posted by: thebigcance ® 05/25/2009, 10:24:06 Author Profile eMail author Edit

alrite pal, let me give u an example, there is a a high torque equipment called pug mill normally used in ceramic industries for extrusion of clay in the form of large blanks........ so here the shaft carries series of balnced augers....... we were using a clutch system before, for engaging and disengaging the shaft, there was a problem, the bolts which were uniting the motor shaft and the auger shaft with the clutch system, shear due to sudden engaging and disengaging......... so we r now using variable frequency drive.........where u can gradually increase the speed and close it the same way, try using a vfd (variable freq. drive. its safe for high torque mechanisms. mathematically, power is torque X rpm ( mechanical power) power is V x I X power factor(not more than 1) electrical power equate these 2 formulae u get, V x i x 0.9 = T x RPM, FROM OHMS LAW, I x R x I x 0.9 = T x RPM, R IS (120 x f)/P, WHERE F IS FREQUENCY AND P IS NUMBER POLES, NOW KEEP THE VALUE OF TORQUE CONSTANT AND TRY DIFFERENT FRQUENCIES, U CAN HAVE A SAFE DESIGN, PLOT A GRAPH, U CAN CHANGE THE RPM SLOWLY INCREASING, IT ATTAINS MAXIMUM RPM FOR WHICH THE LOADS CAN BALANCE AND IT DECREASES GRADUALLY............ THIS IS A THEROTICAL METHOD, U DONT HAVE TO DO THIS, JUST KNOW WAT IT IS, TRY USING A VARIABLE FREQUENCY DRIVE.......... ALL THE BEST......... KEEP IN TOUCH......... KNOWLEDGE IS VALUABLE............ PLS SHARE IT............ REGARDS RAM.............

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Posted by: korena ® 05/25/2009, 22:43:26 Author Profile eMail author Edit

Well, my axis is horizontal, I'm still working on the selection of bearing, but I know its a big ball bearing(9 mm inner diameter) that has to withstand a radial load way less than the maximum it can take which will have a great effect ( I suppose) on the friction factor(u), but I am yet to figure out the (u) to be considered in friction calculations ... About the VFD, Im not really familiar with its applications, but from your post, I understand it is used for variable speed control and shock absorbing ... if Im correct, then my system is rotating at an extremely slow constant rotational speed(1 RPM) , and accelerates to this speed at a rate of 0.025 rad/s, it is going to start and stop frequently though, so, do u think this would have a significant shock effect that has to be taken under consideration ?

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Posted by: jboggs ® 05/26/2009, 00:31:43 Author Profile eMail author Edit

Speaking from 30 years of experience, I would say you are going about this a little backward. Before you get too bound up in the calculations of torque, acceleration, and the like, you should first more fully define the mechanical aspects of the system. In my opinion the most critical factor might just be bearing placement and specification. Your speeds and accelerations are very low, and the selection of available drive systems is very wide. If you get the mechanical arrangement right, you can get a lot of design help from any one of many drive suppliers.

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