Re: Need speed switch for DIY funicular/hillside elevator

["B Fuhrmann" <b-fuhrmann-usenet@xxxxxxxxxxxxxxxxxxxxxxxxx>]

> Dave Houston wrote:
>> If I understand correctly, you want something that will automatically
>> activate if the spool starts turning too fast.
>>
>> Could you adapt this idea?
>>
>>      http://www.msha.gov/S&HINFO/TECHRPT/HOIST/PAPER5.HTM

Jeff wrote ...
 > Dave, yes, that is helpful.  It demonstrates many techniques I can use.
> Althoug I'm still limited as to how to build a similar system myself,
> it should give me some more terms to google to see if there is an off
> the shelf solution I may be able to adapt.
>
> I especially liked the rope brake discussions.  Although their solution
> used compressed air, I could use some kind of spring powered mechanism
> (on cart) to clamp down on a fixed cable that runs from top to bottom.
> I'm still at a loss though as to how to easily trigger it on the speed,
> although obviously a simple solution may be out of my reach.

Instead of an air compressor you could use spring loaded brake blocks that
are released by a trigger.  If properly designed, a trigger and sear
assembly takes almost no force on the trigger to release the object.

For tripping the trigger, you could use a centrifugal governor design like
the speed regulators on early steam and gas engines
www.physics.montana.edu/demonstrations/video/1_mechanics/demos/centrifugalgovernor.html
http://www.gyroscope.com/d.asp?product=WOODGOV

Have a pulley that is driven by the cable spin the governor and you can have
the weights hit the trigger to clamp the brakes on.
Since you intend this system to be used rarely and only in an emergency,
simpler is likely to be more reliable.
I expect that most of it's use will be in testing that it works reliably.

If you choose your brake materials well and adjust the clamping force, you
can walk the line between stopping so fast that the people on board are
injured from the impact and being so slow that they don't stop.

If you want to get fancier, you could use the regulator in it's original
method to adjust a control lever that controls the braking force.

"Robert L Bass"  wrote ...
 > A centrifugal brake should do the job.  Ideally, the brake engages as the
drum starts spinning fast. As the brake slows the drum, it
> eases up a bit, allowing a safe descent.  ISTR they used something like
> this on the tram at a ski lodge in NH.

You might be able to do this inexpensively by using centrifugal clutch from
a go cart.  Instead of connecting between the drive and driven system, you
could connect it to the cable (requires a good grip between the pulley and
the cable) and a resistance element.  As the clutch spins, it locks up and
the resistance element comes into effect.
The advantage of this would be that the car would never come to a stop and
would return people to the bottom of the hill.
The disadvantage is that it could be difficult to adjust this system to
limit the speed so that the car is moving slow enough when it gets to the
bottom.

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Based on this being rarely used safety device.  I like the idea of simple,
even if it requires that people get off part way up the hill.

Bill Fuhrmann




--
Bill Fuhrmann