Drive System on a 4-wheeled car 3

[mizzoumech]

I am currently looking into designing a 4 wheeled car that will lift steel coils and transfer them to a different location. The following parameters are as follows:

Wt of Car w/Steel Coil: 125 kips
Velocity = 6 in/sec
Distance = 50 ft
Drive Shaft Dia = 3 in
Coeff of static friction (stl to stl) = 0.78
Wheel Diameters = 12 in

The car wheels will be steel and will be riding on steel rails. The drive system will consist of an electric motor with a shaft mounted reducer. The back car axle will be the drive axle. I am assuming that I will need to calculate the torque and power required to move the car from a static position. This would include overcoming the weight of the car as well as the frictional force from the steel wheel to steel rail contact. I believe I need to look at the total weight of the car when I am calculating the reducer torque. Is this correct? Is there any other item(s) that I need figure?

 

[drawoh]

mizzoumech,

You have asked a very broad question that makes it sound like you are in over your head.

There ought to be someone at your site who understands cars like this, and who can answer your questions. How do the coils get on and off this thing? How are you going to stop it rolling? Is there hardware at your site people would prefer you used? If nothing else, sixty tons of equipment rolling back and forth, sounds like a safety hazard. Perhaps you should refuse the work.

JHG

 

[MintJulep]

Your assumptions are fundamentally incomplete, and what is there is incorrect .

 

[dvd]

Where did you get the coefficient of friction? That is a value for sliding friction, not rolling friction.

 

[Medeski]

Perhaps the Demag website for wheel blocks may be of some use.

http://www.demagcranes.com/Products...ck_system/Product_details/index.jsp?prospekte

I haven't hunted around, but they are likely to have some technical data/worked solutions for similar situations somewhere in their brochures.

Best,
Medeski

 

[mizzoumech]

I have reviewed my P.E. book and my Mark's Handbook. dvd is right that this is rolling friction and not sliding friction since the wheels will utilize pillow block roller bearings. I am upgrading an existing working car design that another company built. Since I wasn't involved in this existing working design, I am leaving no stone unturned so I wanted to start from the basics. Thank you dvd and Medeski.

A good engineer knows what he doesn't know but can always eventually find the answer...Never be afraid of asking a question. Even if some of your peers might think it is stupid.

 

[MiketheEngineer]

They make "trucks" or for lack of a better term "baby locomotives" that may solve your problem...

 

[zdas04]

Read your original post again. Can you honestly say that you don't think it reads like a homework problem? An engineering problem would not have the statement

I believe I need to look at the total weight of the car when I am calculating the reducer torque. Is this correct? Is there any other item(s) that I need figure?

Engineering is about the details, not about the physics. The physics defines the boundary conditions. Engineering places the components within the boundaries. I would hope an 11 year engineer who is either studying for or has his P.E. would know that.

David

 

[dvd]

Wheels occasionally have to roll over debris on the track, so don't get too carried away in reducing friction. You may need some reserve for unanticipated events.

 

[MikeHalloran]

Just off the top of my head, 15+ tons on a 12" wheel sounds a little high, but don't take my word for it. Look up manufacturers' crane wheel ratings, which I think require you to select a rail section first....



Mike Halloran
Pembroke Pines, FL, USA

 

[dvd]

Be careful with cast iron pillow block bearings which may receive shock loading. Make sure that the loading direction and magnitude is endorsed by the bearing manufacturer. Consider steel housings if there is any question.

 

[kingnero]

Coeff of static friction (stl to stl) = 0.78

That is a common value found on the 'web, however I've yet to see that in real life.
Could someone elaborate that for me, or give a situation where friciton as high as 0.78 (or about that) is happening?

my findings:

http://www.youtube.com/watch?v=558Htmux6UE

And that shows a more common and realistic scenario.

 

[CoryPad]

Any of the friction coefficient values like that are from studies in vacuum from half a century ago. It is amazing how they have been perpetuated with no fact checking for so long.

 

[MiketheEngineer]

King -

Maybe rubber tires on dry concrete. A Cf of .78 for steel on steel is unheard off. That's why trains use steel wheels and steel rails. The Cf is very low which makes starting and stopping a bit of a problem - but once up to speed there is virtually no friction.

 

[imcjoek]

The Cf is very low which makes starting and stopping a bit of a problem - but once up to speed there is virtually no friction.

I'd say the hardness of the steel allows for low rolling resistance due to less deformation of the wheel. The crappy coefficient of friction is merely an unwanted side effect. Hence adding sand, grit, etc between wheel and rail when extra tractive effort is desirable.

 

[zekeman]

Since this car is going only 50 feet , why not design it like a csble car. It might be simpler and wheel friction dependence would be eliminated as well as starting and stopping.
Just a thought....