Horse power calculation?
Horse power calculation?
(OP)
Can anyone tell me how to calculate the HP (for an electric motor) required to startup and drive the system in the picture? I have tried it several differnet ways but I keep getting different results. The torsion springs are designed to be at equilibrium in the position shown (at the center of the stroke). Would I be better off to design the springs to be at equilibrium at the bottom of the stroke?
Hey, how do I insert a picture?!
Hey, how do I insert a picture?!





RE: Horse power calculation?
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RE: Horse power calculation?
[IMG]http://tinypic.com/faxzqu.jpg[/IMG]
thanks beggar
RE: Horse power calculation?
I wasn't able to exactly understand from your picture but these equations along with forthcoming replies from others may help:
ht
RE: Horse power calculation?
RE: Horse power calculation?
RE: Horse power calculation?
there is also work done in the horizontal plane, as the 6700 lbs gets accelerated first one way then the other. The acceleration at the end of the crank is (340(2pi/60))^2*0.8125 = 1030in/sec2 = 86 ft/sec2 The MASS is 6700/32.2 = 208 slugs (don't ya love that unit), and the force that the crank applies is 208*86 = 17874 lbf. the velocity of the end of the crank is (340*(2pi/60))*0.8125 = 29in/sec = 2.4ft/sec. then the work is 17874*2.4 = 43090 lbf.ft/sec = 78 hp.
combined is 112+78 = 190 hp
maybe there should be something about the sinusodial motion, but that's what you get for free !?
RE: Horse power calculation?
What would you say if I told you that I saw the same exact system, except instead of 6700 lbs it was 3700 lbs, running easily off a 5 HP motor?
RE: Horse power calculation?
RE: Horse power calculation?
RE: Horse power calculation?
With you system you are moving the platform horizontal 1.7” and vertically .812” with half of this being in the up stroke and half in the down stroke. I would think of this more as shaking a spring mounted playground horse instead of lifting. Or think of the force to deflect the platform down and back .4” and .85” to get a start on horsepower.
Barry1961
RE: Horse power calculation?
RE: Horse power calculation?
Also, since you haven't specified a ramp-up profile, I don't think you can really work out a startup torque either.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Horse power calculation?
Could it be that what you are probably really after is some mechanical IMPULSE on a system that has a certain natural frequency? I think Barry was on the right track with his spring rate comment. The impulse on the system would add up to eventually give some sort of steady state vibration. This oscillation would necessarily be less than the stroke. Taking advantage of the mechanics of a system with a natural frequency of vibration would allow low HP for vibrating a big mass.
It also seems like it would be impossible to have a rigid connection to your load...you'd kill your motor bearings because of the transmitted load. The pulling/pushing would have to sprung/dampered to get some sort of suitable resultant force without mechanical damage to your prime mover.
Then, again, I could be wrong...I just knocked off my second glass of wine
TygerDawg
RE: Horse power calculation?
The system I am describing currently exists. The current system has an 5 HP, 1800 rpm motor with a 3.5" pulley on it. The pulley is attached to an 18" pulley via 2 V-belts. The 18" pulley is attached to an offset shaft. The shaft is 2 3/8" on the ends and 4" in the middle, giving an eccentric radius of 0.8125 inches. The connection is quite rigid. The connection consists of 2 tear dropped shaped plates that are 1 3/4" thick. These plates have a flange bearings on each end. One end is attached to the 4" shaft and the other end is smaller probably attached to a 2" shaft(which is connected to the shaker bed). The offset in the 4" shaft causes a reciprocating motion in the connection. The current mass is a 3700 lb shaker bed, the customer wants to add 3000 lbs of abrasive resisting plate to increase the life of the bed. The current system has been in operation for around 50 years. I find it hard to believe that the power required by the new system could be much over 10 HP. The reason I started this thread, however, is because I was coming up with much higher power calculations. If I go to the customer and tell him that he needs a 150 HP motor he is going to tell me to get the hell out of there.
RE: Horse power calculation?
In the distant past, I reviewed the differences between sub-resonant feeders and "brute" force feeders. Your low horsepower implies a sub-resonant feeder, but your approach seems to be applying a brute force calculation.
I have not worked out the math for myself, but I have had discussions with vibratory feeder company reps in the past regarding liner weights and the "what if" the owner wants to put on thicker liners in the future.
I suggest contacting a vibratory feeder company and see if you can talk to an applications engineer.
Some names to Google include: General Kinematics, FMC, Jeffrey.
Good Luck.
Cheers,
CanuckMiner
RE: Horse power calculation?
"The system as drawn needs no power at all, once it is running ..."
so we've discovered a perpetual motion machine at last !
quick, let's rush out to the patent office
RE: Horse power calculation?
I was looking back through all of the posts and I suddenly noticed something that alarmed me. I saw that you said that the system was operating at 340 Hz and I started to second guess myself, there is no way its going that fast! Then I realized that it is not moving at 340 Hz it is moving at 5.7 Hz=(340 rev/min)/(60 sec/min). I feel a little better now, but that still seems pretty fast. I think I might take a trip over and tach this machine.
RE: Horse power calculation?
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Horse power calculation?
maybe something missing (in all the posts, including mine) is the fact that the stuff on the shaker isn't rigid so much of the shaking motion of the table ends up in the stuff on the conveyor ... again, greg, another loss to the system shown (since it isn't, shown).
RE: Horse power calculation?
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Horse power calculation?
RE: Horse power calculation?
To find power consumption, we need to determine where the input mechanical energy is being dissipated or moved out of the system.
I would think the primary energy consumption path is the frictional heating of the material in the shaking table, with a secondary energy output of the kinetic energy imparted to the material which exits the shaker. Having said that, the analysis to arrive at the required power becomes very complicated, and probably only available from tests or empirical data for similar equipment.
Since the mass of the system is nearly doubled, you could conservatively expect the starting loads to approximately double. This would indicate a similar 10 HP motor is probably safe from a starting standpoint.
As far a steady state loads, the new wear material may cause different frictional character on the table, and this could change the power consumption. Steady state power requirements could go up or down, and this is unknown. Engineering judgment tells me that the power will probably be less than double the original, so the 10 HP motor is again OK.
RE: Horse power calculation?
Will you need to run at a different speed.. or change the springs...or derate the machine...etc?
"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams
RE: Horse power calculation?
RE: Horse power calculation?
Thank you, that was the point that I was trying to make earlier...
RE: Horse power calculation?
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.