second posting High Velocity using Block & Tackle

Thanks for the help. We have thought of the inertial forces in the spinning pulleys, and the fact that there will be significant stretch in the cable. Actually the cable will be under a working load of as much as 20,000 lbs. Using kinetic energy we have figured our power requirment just for the pulleys at 2000 hp. I will also mention that we will have a large capstan (winch) at the other end of the cable to reset the system. These capstans are equipt with a brake and can provide a slight constant damping force to oppose the oscillatory action of the cable. The capstan will also be responsible for slowing the cable when the required velocity is reached. The hydraulic rams should stop themselves easily enough. A couple more questions: Any thoughts on accelerating cable over a pulley that fast? will it slip? heat up? etc. Any thoughts on accelerating hydraulic pistons that fast? It will require huge flow rates. (300gpm) Shock loads on the cable?

Thanks again

Joshua

Dear g3_josh:

KE = 1/2 * 20000/2.205 * (250 / 2.24)^2 = 56.5 Mj

Averaged over 2 seconds is 28000 hp. Unless I slipped a digit.

Stretch in the cable will be very great. Which means you will need additional displacement.

If it slips, it will not transfer as much energy to the pulleys. Most likely slip will not be an issue by extending the centers of two pulleys with a hydraulic cylinder. Slip is usually only an issue when you are driving a pulley with a rotary motor.

It will heat up.

Not much acceleration with a 100 to 1 ratio. Only ends up at a slow walk.

You could use piston accumulators to supply some of the horsepower.

Which can be minimized through "metered" valving or a baldder accumulator in the hydraulic stream.

Look closely at the bearing stresses at the hubs of the pulleys, and on the cable to the pulley.

Good luck, and *duck*.

David A. Smith