Re: Need speed switch for DIY funicular/hillside elevator

[astutesolutions@xxxxxxxxxxxxx]

Rohan, Thanks for the comments.  Yes, you have pretty much summed up
the situation.  What you speak of would be a good solution if there was
an easy way to determine the overspeed condition without any expensive
electronics or hydraulics.

The dampening of the cable is something I hadn't considered, but is a
potential risk.  I'm hoping that since there aren't extreme loads on
the cables (500 lbs per cable at 30 degrees) that the whiplash effect
would be minimized, but I could be wrong.

Thanks!
Jeff

rhamer wrote:
> I hve found reading this thread most enjoyable and commend you on your
> work to date.
>
> I am slightly confused as to what particular problem you are trying to
> solve, although I guess it all falls under the general heading of
> "Saving your passengers from running out of control down the hill"
>
> I think you have to decide where the reasonable points of failure are
> and accept that other potential points are ruled out due to good
> design. This will then determine where and how you need to provide the
> appropriate braking mechanism.
>
> Already you have decided that a single cable is an unacceptable single
> point of failure and so you have duplicated it. Given that each cable
> is rated at many times the actual load I would consider that 2
> simultaneously broken cables to be such a small possibility that it
> could be safely ignored (however I have not seen such things as the
> attachment points at top & cart). Consider the chairlift as an example
> of a single cable design.
>
> From what I have read here so far, I would think that your major area
> of concern is in motor or the coupling between the motor & drums. I'm
> also assuming that the anchoring of the motor & drums is designed to be
> solid under any sort of reasonable conditions, much like you don't think
> your whole house is going to slide down the hill, because it has been
> designed no to, so doing the same with the motor would not be too much
> of an engineering challenge.
>
> So in my opinion the part you are lacking is the over speed detection
> and braking of the drums.
>
> I would consider solving the problem by having a third outboard disk or
> drum (like a car disk or drum brake) that has shoes that are held off
> electrically (either directly or indirectly via hydraulics) I would
> then pulse count the rotation of the drum to calculate the speed and in
> the event of over speed set the brakes. Correct operation of the pulse
> counting could be verified during the first couple of seconds of
> operation otherwise the brakes should be applied. You could probably
> source most of the bits using the anti locking brake system off a car.
>
> I would also provide some form of dampening on the cable, probably in
> the form of a small car coil spring, rigged up in line, with the cable
> ends passing through it so it is working in compression. This will stop
> the cable from potentially whipping should the braking be a bit sudden.
>
> Anyway, just my thoughts.
>
> Cheers
>
> Rohan
>
>
> --
> rhamer
>
> 'HAMFIELD' (http://www.hamfield.com.au)
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