Jack Screw Actuator for Whitewater Park

[shipleyscott]

I am trying to design an obstacle for a whitewater park that I am working on. The obstacle is a swinging barn door type gate that is typically aligned with the current. The hinge pins are at the upstream side. At the downstream end I want to have an extender that is attatched to a vertical jack screw. The extender forms the hypotenuse-link between the top of the jack screw and the bottom of the barn gate.

So here is my question: The reason I am using a jack screw is that I want the gate to be adjustable by visitors to the park through a crank wheel. However, this arrangement puts a tremendous thrust load on the jack screw and I am worried about binding. Can I just oversize the jack screw or is this a bad design idea from the start? The total thrust load is approximately 13,000 lb force. Due to space availability the jack screw must remain vertical.

Scott

 

[unclesyd]

I wouldn't visualize any problem with the Jack screw if used within it's design limits. We have them operating continuously and once a year and I can't recall any problems with overloads or sticking.

We use products from both the following companies. We have changed several screws from the Acme Type to the Ballscrew Type. I don't know why as stated there have been not problems.

There is some very good information on these sites.

http://www.nookindustries.com/ball/BallCatalog.cfm

http://www.duffnorton.com/products/mech.aspx

 

[Barry1961]

Is the screw going to be in the water or outside the chute? Will the screw have grease on it? Can you use counterweights or springs to offset the load?

Try to find a way to cheat!! Can you divert part of the water into a drum counterweight to raise the ramp?

Acme screws will not back drive. Acme screws are not very efficient and hard to turn the first few revolutions if left under load. Using high pressure grease and oversizing the srew will help the start in high load applications. Of course use high pressure grease.

Ballscrews will back drive and are very efficient. They are very good at high speed, high cycle applications. They also cost much more.

Barry1961

 

[shipleyscott]

I guess the thing I'm most worried about is the side load. If the bar bends won't I have trouble with binding, etc?

 

[Philrock]

Side loads are clearly the critical issue here. Common practices where side loads are involved:

1. Use an oversized rod (oversized for the thrust load).

2. Use an internal stop tube around the rod that prevents the rod from fully extending. This means you must size the nominal length of the actuator for the desired stroke plus the stop tube length.

3. Do all the calculations for buckling, friction, bending, misalignment, etc.

 

[sreid]

If people have to position the gate under load, you are going to need a large mechanical advantage and low friction for people to move 13,000 lb. Even then, it will take some time and effort. Sort of like jacking up a large truck.

 

[unclesyd]

If you use the recommendations of the actuator screw provider, provided you give them the complete picture, the actuator will take anything withing these design parameters and a little more. 13,000 lbs. is no problem.