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horse power .. toss me a bone here
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Posted by: randykimball
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02/15/2007, 10:26:48

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I have a 4000 lb load on level ground (concrete).

I want to move it by rotating 5" diameter wheels. I will be applying torque to two wheels independantly via hydraulic motors.

I want to get it moving at a slow ramp-up (accel) speed to reach
a max of 50 feet per minute.

My brain is blocked on this one ... dauh..

How much HP or torque do I need?





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Posted by: zekeman

02/15/2007, 22:50:47

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If you are talking constant acceleration, then the torque is constant on the wheels and you can write
T=FR ( true even for variable torque)
Ft=Mv
where
T=torque
M =mass=4000/32.2
R=heel radius
v= final velocity
F= linear force on mass
t= time
From the 2 equations
T=MvR/t
So you see the torque in this case is inversely proportional to the time required for the excursion.
If you don't have a constant torque control capability and can state the torque/speed characteristics of the motor then
T=T(v/R) i.e. T is a function of angular speed v/R
and the second equation is
Fdt=Mdv
and therefore
dt=Mdv/F=Mdv/T(v/R)/R
Integrating the two equations, I get
t=MR*INTegral(dv/T(v/R)
simplifying
t=MR^2dw/T(w) where
w= angular velocity of the wheel
You would need to integrate the right hand side numerically over the limits of 0 to vfinal/R







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Re: horse power .. toss me a bone here
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Posted by: maytag

02/15/2007, 17:47:33

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axle torque=force*radius
As you know the max T will be required to get the 4000 load started-only about 20lbs per 1000lbs required to keep the load moving after that. I think it will be somewhat like the coefficient of friction for steel on steel (maybe .3 or so)
Speedwise the 50ft per min.with a 5 inch wheel is about 38 rpm unless I have misfigured(I've just come off nite turn)and my books are at work. Size the motors from this data (Torque=motor displacemennt*PSI differentual across the motor/24*3.1416-then size pump for needed flow/pressure required by motors and then last size electric/gas /diesel motor. HP=GPM*PSI/1714*pump efficiency
From my experience even though I would be using 2 motors they would be sized where one would be sufficient. The motor formula is not what I normally use but as mentioned earlier I'm home and most of my books are at work.
Are you going to use one pump per motor or split flow from one pump for the two?? Good luck, Maytag







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Posted by: randykimball
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02/15/2007, 22:34:25

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Driving two motors with one pump powered by a DC 12 volt motor. This gives me a chance to use the pump at high RPM with a small DC motor & pump, gaining leverage. The hydralic motors will be on steering wheels, on a split system so they act like a fith member.

Figuring the torque requirements is NOT in my comfort zone.

Thanx for your help, any help. It is an important application.





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Modified by randykimball at Sat, Feb 17, 2007, 00:55:29


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Posted by: randykimball
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02/17/2007, 00:46:44

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thank you all for the help...
..solution achieved...




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Posted by: zekeman

02/17/2007, 13:45:36

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I'm puzzled as to why you chose a hydraulic solution. Since the maximum RPM you need at the wheels is about 60, I would think you could have used your 12V DC motors (or a gearhead) with a gearbox having a gear ratio of 30:1.
Just curious.







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Posted by: randykimball
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02/17/2007, 22:52:59

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The motors go on 5" diameter steering "casters". By using hydraulics I can get a tremdous leverage with the adavantage of an ablosute safety brake when the hydraulic directional valve is in block mode. Also there is a need to be very rugged in a space fit parameter. ..and.. My experience is that geared DC motor sets aren't all that rugged within the cost bracket.

Also, with a split plumbed hydraulic motor concept, I get the same effect as a fith member to handle positive drive but with variable velosity per wheel during turns. This application is always on a flat concrete surface, so a non-traction wheel is not a problem.





The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

Modified by randykimball at Sat, Feb 17, 2007, 22:58:37


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