My dad and I built a homemade hill lift (in Europe refered to as funiculars) in Eastern Tennessee. You can see a working demonstration and picture of it at:
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The tram works fine, but I am trying to figure out some kind of simple safety mechanism in the event that the spools break loose from the gearbox or shaft and start rotating freely. Since my wife and kids ride this thing, I'd like some kind of backup solution in the event of major catastrophe. We are using 2 cables instead of one even though one can handle 5 times the max load, and we have a braking motor to stop, but both of those would be moot if the spool spins out of control.
I am thinking of having some way of measuring the outfeed speed of the cable (or spool) and have some emergency brake apply if a limit is exceeded.
Any suggestions? I thought about putting fan blades at end shaft of the spool to have air slow it down, but that would be a little unsightly. I'm looking for a simple solution, one preferably without a computer since this is outdoors and needs to be functional 100% of the time. I'll take any flames in stride on this point. I realize that this group is about computer automation, but its the only one similar to this kind of project I could find :-)
Since there is always tension on the cable, regardless if the car is going up or down, can you fix a spring loaded brake to the car that is held off by the tension of the cable?.
I like Doug's idea of the automatic brake. I also think you should put solid sides on it to keep people from "dangling their legs" through the railing like I observed in one of the movies. I also think you should employ some sort of gate, permanently mount the controller and incorporate a safety switch that would prevent the device from moving with the gate open.
Solid sides, yes. The vid was from the weekend we first got it done. I plan on finishing it with side pickets such as a deck. I also need to put the rail back up on the deck with a gate so we can keep small kiddies or dogs from falling off. I can put a limit switch to prevent it from running when open on the main deck, but don't really have a good solution for that on the cart since it is wireless. I think it will eventually be more of an education thing. The legs dangling although not prefered was actually not too worrisome at that point since the front of the cart is 4 feet off the ground. But eventually the sides would prevent that.
As to the slack, I was originally thinking of something like that, but with the cable being so heavy, there is actually much slack midway down in the cable when it is descending, and there will be even more once I increase the speed of it (variable speed controller). That would work well in the event of the cable snapped, but that is pretty unlikely having 2 wires snap at the same time.
In the event of a free spool, there are 2 places I could slow it down. Either up top at the spool with some kind of cable grapple, or on the cart assuming a I had a fixed cable running from top to bottom that the cart straddled and ran through some eyebolt/pulley scenario.
The trick is, how to determine when it is going fast. I almost need some kind of centrigal device on the cart or at the spool that cuts a cord or triggers something when it gets going too fast. I don't have to worry about a a false alarm start surge because the motor controller ramps up the speed when starting.
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.
At the end of the drums is part of the 1.25" diamater shaft that sticks out. I could increase the torque on it by using 2 different gears (large one on shaft, smaller on compressor) connected with a chain to increase the rotational speed.
When going downhill, even if it was in resistance mode, the motor would overpower the slowdown, but in a freespool situation it could slow it down as desired.
It would be nice if it was able to only apply torque in one direction like a bicycle wheel. I wouldn't want it to torque on the trip up, but just on the trip down. I suppose I could use a bicycle setup for exactly that purpose, but I think my dad would scoff at the non-industrial sizing of it, lol.
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.
Don't know if this has been suggested but here goes.
In your desire to keep this a simple system to control a loss of cable or drum think about this.
Since it appears that your tram is straight on an incline you could affix a single cable between the rails from end to end. This would be under your tram. On the tram bottom have it pass thru a spring loaded clamp apparatus that would have a pivot lever with a protrusion thru the floor. This protrusion would have a foot pedal mounted on top. The operation would be that a passenger would just stand on the pedal which would release the clamp on the cable thus allowing the tram to move. If a disaster should happen it would a matter of lifting your foot and the clamp would stop the tram.
Also your drive motor would or should have either a slip clutch or a overload trip to protect the rest of the system. With all in place you could use it to help stop and hold at the other positions you have indicated.
In some applications it is called a Dead Mans Stick or Switch. Such as on a train or trolley.
It may not work exactly as described above but it may start the seeds to grow.
Les, thanks. The fixed cable with a spring clamp is something I thought of, the only problem is that the deadman switch wouldn't work because part of the design is that there is a call button at the top and bottom to recall the cart in the event it is at the opposite end. It was also suggested that a mechanism such as this could release when the cable tension was released, but due to the stiffness of the cable and how the cable is already somewhat slack when the cart travels down, it makes it hard to set up the trigger, with the exception of if both of the "pull" cables broke.
I do think that the fixed cable is about the only way the cart could have something to "grab" onto similar to the method you describe. Grabbing the rails would be difficult because the sides are circular (pipe) and there are angle iron pieces that extend beyond the plum part of the pipe leaving less than half of the pipe to grab.
What would be nice is if there was a way to have a pulley mechanism on the cart that spun a cog or something such as a pnuematic pump that the faster it went it applies more force to say a brake caliper that would grab the fixed cable, as suggested by Doug earlier.
Jeff wrote ... > Dave, yes, that is helpful. It demonstrates many techniques I can use.
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
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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
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.
Yes, something like this might work. The spring/lock cable grap could be held in the open mode almost like a mousetrap with a little force that is easily triggered provided it could be done so that no jostling or sharp inpact would force it to snap.
Another thought along a similar lines is to have two brake pads pushing on the cable with a spring applying the force (like an emergency brake on car?). A fulcrum weight could hold the tension off of the spring keeping open and something like that centrifugal governor could lift up on the weight at higher speeds. Cool. Thanks!
I think what you want is something which loads the shaft in proprtion to the speed so that at normal climbing speed there would be minimal load while at the higher speed of a runaway, it would create a maximum load, slowing the descent. It may prove that an air compressor is inadequate but I think you understand the general idea.
I do not like any of the friction-based suggestions. I think they present maintenance problems and will, themselves, be prone to catastrophic failure. You want something that requires little maintenance and is fundamentally failsafe.
Also, I don't like anything that's passenger operated since it might carry someone unfamiliar with its operation.
I really have no idea how big an electric motor needs to be to act as a brake when it is generating electricity into a resistive load (as shown in the first link I cited) but, individual motors on the wheels of the tramcar might be another possibility.
BTW, I can just remember (actually, these days it's more a matter of remembering remembering) when the Mount Adams Incline still operated in Cincinnati. It was a little larger than your funicular, being designed to carry streetcars. There were 4-5 funiculars in Cincinnati. The bottom of the last link, below, has links to photos of the others.
It does get a bit challenging does it not. Diverting from the simple a bit you could consider this.
Since you have already made the wireless for control of the unit could you then incorporate a solenoid on the deadman switch that would override the foot pedal for a one-time trip. This could be set up in relay logic that would respond off a momentary push button at either end. Once the tram reached its new position it would trip a limit switch and return all functions to normal. It would require that some power on the tram but this could be accomplished with a battery with some indicator when the battery gets low.
I can see some problems since this will not be 100% fool proof. (or idiot proof as some would say) but you can do some rigorous training of family an friends since this is not for public use.
Although I think the speed governor with a brake pad on a fixed cable would be the better solution in terms of noise and reliability, it would be harder to implement than a direct drive to an air compressor. But the AC would be noisy (pap-pap-pap-hssss). Either would require periodic maintenance I suppose.
Agreed.
That would require a battery to energize the stator (I th> Jeff,
Yes, that is a bit more complex. I would have to have a battery on there and keep it charged which would pose its own problems for maintenance.
One whimsical solution, perhaps I should have a parachute pull a cotter pin, lol. If I could count on the wind not pulling it on a windy day.
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