Big Gate

[007Driver]

Hello all,

I just graduated from mechanical engineering and Im feeling silly about having difficultly with my first design task as a newly employed EIT. This is what I have been working on:

A set of driveway gates for this really nice mansion, these gates are going to be big and heavy and they want them to be all automated, a clean smooth outer appearance with low upkeep.

The gates: 7 feet wide each, 6 feet tall, 2000 pounds each (made out of cast iron and solid steel backing)
Bearings: Tuff Cast machineable resin, the top bearing runs on a shaft 1.5" shaft as does the bottom, the main holding post is a 3"X3" solid steel bar. The bottom bearing has a seat of 4"O.D. for the gate to sit on ( my thrust bearing to hold the weight of the gate ) and with a small radius in the inside of the bearing the surface area of the thrust bearing is ~8in^2

My Question:
I am having troubles designing an automated gate opener, the simplest idea I have come accross is running a bar between the two gates at the bottom and having a rack and gear at the bottom of each gate (gear of 12" DIAM.) and along this shaft having a industrial screw drive push this rod side to side to open/close the gates in unison. I need to figure out how much force I need to close these gates. The co-efficient of friction of the Tuff Cast is .2 So originally I worked out it would take 400lbs to push the gate open, but im not pushing it, im rotating it open, so is this value still mean something though I am turning the gate on a shaft and not sliding it?? The moment of Inertia of these gates is quite large and that value seems very small to open the gates. So how much force will it take to swing these open/close?

Other info:
Id like the gate to swing open/close (90 degrees) in about 20 seconds.

Appologies for the lengthy question, but Im freaking out here not being able to do what seems to be a very simple problem :S

Thanks, John

 

[steve1]

Possibly your task is not to "design" an automated swinging gate but rather to "specify" one. You would be responsible for the installation drawings and the proper specification for the assembly, but not the design of the actual mechanism. That item would be purchased from a manufacturer. A quick internet search on "automated swinging gate" revealed lots of leads.

 

[Tomfh]

Definately specify one.

 

[MikeHalloran]

Don't put the drive at the bottom unless it's dirt- proof.

Nothing is dirt- proof.



Mike Halloran
Pembroke Pines, FL, USA

 

[007Driver]

I spend the first full day trying to track down a "buy and install" opener, there are no units available for this weight of gate and looks how the customer wants it. If anyone sees an opener thats FULLY hidden and can handle 2000 lbs, I would be very happy.

 

[Ussuri]

Silly question, but if the manufacturers can't design one to meet your clients requirements could it be its not possible? I would be concerned about even trying to design a one-off bespoke one myself because if its not your field of expertise you will undoubtably miss something.

In all honesty, I would have thought that speaking to a manufacturer and asking them to design you bespoke one would be easier than trying yourself.

 

[Tomfh]

I did a search and came across this:

http://www.gatedepot.com/prod_ramset/broc/ram_30-30.html

And here's one that's nice and discreet:

http://www.gatedepot.com/prod_faac/detail/400.htm

 

[DaveVikingPE]

Northern Tool sells gate openers,

http://www.northerntool.com.

The ones in the catalog on my desk only go to 1,000 lbs., though.

 

[MikeHalloran]

Oh, yeah. I wouldn't put a rack or even a sliding bar in the ground.

The mechanism also needs to fail gracefully, sort of, when something gets stuck in a gate.

I'm thinking friction drive with rubber tires. Maybe near the hinge, rolling on a half-drum of say 6" radius, or at the outer edge of each gate, bearing on the driveway, which requires much less torque, and can bear some of the weight.

Neither of those bear any resemblance to most of the openers I've seen for large gates. Those fall in two classes:

- Sliding gates, like pocket doors, on fixed casters or a track, driven by a roller chain.

- Pulled out of the way by a sliding actuator with a fairly long stroke, attached to a clevis around mid-span of each gate. The 'fixed' end of the actuator attaches with another clevis to a post alongside the drive, half a gate span from the gate. These are positioned to hold the gate closed pretty well, and are sometimes hidden by horizontal decorative features in the gate when the gates are open.

To hide the mechanism almost completely requires the use of some high torque device, like a hydraulic rotary actuator. The actuator itself is simple; the support system is not.

I wouldn't worry too much about mechanically synchronizing the gates. If it's an actual requirement, it makes more sense to do it electrically, even with mechanical or hydraulic actuators.





Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

So, what safety system do you put into these two ton JAWS OF DEATH?

What happens if the power fails?



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Ron]

Why not buy a pair of railroad crossing arms, modify the guard to receive a decorative aluminum gate, and have a bascule-type gate. Would take less space (except overhead) and they are extremely reliable.

Gate pickets could even be hinged so that they become like a solid piece as they close.

 

[MikeHalloran]

Safety systems? On a mansion's gate? Hah.

Cutting edges! Autonomous robot machine guns!

In civilized countries, of course you would have to worry about the issues Greg raises.





Mike Halloran
Pembroke Pines, FL, USA

 

[007Driver]

The FAAC 400 model looks like the winner

http://www.gatedepot.com/prod_faac/detail/400.htm

Comes with a warrante that we cant offer the customer if we built it and it handles a gate thats 3 times as long as ours. Also has a nice "soft" start and stop which is nice. And the price looks pretty close to what I came up with a screw drive system.

 

[Grouser]

Driveway gates in So. Fla. are required BY LAW to stop or retract if an obstacle is encountered. A woman was crushed to death by one a few years ago. Check your code.
Cheers.