Re: Need speed switch for DIY funicular/hillside elevator

[astutesolutions@xxxxxxxxxxxxx]

Thanks Robert.  Yes, I'm thinking more and more of a solution like
this, but I'm not as concerned of a breaking cable as I am the
freespool event.  Each cable is rated at 8,000 lbs.  The cart fully
loaded would be around 1,000 lbs at 29 degree slope.  At this slope,
the load would be about 500 lbs per cable which is 1/16 the max load of
a single cable.  So if one cable were to fray and break, the other can
handle the load easily.  I have them going through pulleys, but there
is also a backup attachment to the cart, so if one cable breaks it will
still have an attachment to the other cable.

But, it is possible I think to have the 3rd cable as you mention with a
springed arm of some sort that would "grab" the cable if the tension of
the primary cables released.  I suppose I could adjust this "trigger
point" by adding additional springs such that the trigger tension was
almost to the point of catching.  If I were to set it up such that the
trigger locked and wouldn't let go, I'd run the risk of someone
jostling the cart when they get on, releasing some tension and
triggering the lock.  Perhaps a scaled approach that the less tension
the greater the "grab" would work, if that makes sense.


Robert L Bass wrote:
> Going back to Doug's suggestion, you could install a pivoting arm with a pulley on the end to take up slack in the cable on the
> uphill side of the tram.  The arm would need a hydraulic or spring-loaded strut to draw it up toward the tram.  Slack feeding out
> beneath the tram goes up over the pulley.
>
> The arm mechanically holds open a brake as long as it is stretched down, where it will always remain if there is tension on the
> cable.  If the cable breaks the arm swings up, activating the brake.  The can either be on a third cable or on the wheels.  A cable
> brake should be easier to implement than wheel brakes, but the end result is the same.
>
> The advantage to Doug's idea (as I perceive it) is that it is simple, requires no electronics and should be easy to maintain.  Trial
> and error should quickly yield the amount of tension required to operate the arm and the brake.
>
> Note about safety factors.  When "flying" live actors or moving loads above a stage, I would select equipment rated to hold 10 times
> the static weight of the load.  This would allow me enough margin of safety to stop a load even as it gained momentum before
> reaching the end of the safety cable.  On a slope the load doesn't gain momentum as quickly as on a deadfall.  However, depending on
> how quickly your safety system detects a failure and engages and the slope of the rails, the tram could accelerate, perhaps to the
> point of failure of the emergency braking system.  Not knowing the weight of the tram, number of people who will be riding at one
> time, slope of the hill, etc., I can't say how strong is strong enough.  It sounds as though you've given this careful
> consideration, but double-checking your calculations is never a bad idea.
>