Automatic slow up and down skip car hoist.

[knotian]

I currently have a skip hoist operating with an EV3 controlling the up and down motion of two cars. I have a two barrel drum arrangement with reversed cables so the motor, when it turns the shaft ,is raising one skip and lowering the other. Then the program reverses the motor and the cycle continues.

I would like to do the same thing with a PF motor but cannot think of a way to reverse the motor automatically. I can do it with a single dog for each skip car that catches the skip car and raises it then disengages at the top BUT!! then the car drops to the bottom unrealistically fast.

The only way I can think of is to have a lever on the side of each car that flips a power function reversing switch at the end of each cycle.

Anybody know of another way to accomplish this?

 

Thanx

[letsbuild]

Could you post a video of what you're describing? I have a hard time visualizing it.

[knotian]

I can't take a picture.

Google blast furnace and you will see a skip hoist used to take the ore and coke to the top of the furnace.

[Orcman]

Is this what you're after?

http://www.nico71.fr/gbc-tipper-trolley/

[Jurss]

You could try to connect mechanisms somehow to battery switch, only You need there some flywheel or something with inertia.

Or with pneumatics, something like this

 

[doug72]

Would the inclined GBC lift shown in this video be suitable ?
It uses a M motor powered change over unit and elastic cord to move the trolley which allows the cord to run when car hits stops until c/o unit reverses the drive cord drum. Does not need any PF c/o switches as its purely mecahical.

 

Edited February 14, 2018 by Doug72

[knotian]

Thanks for the ideas! Some good concepts that I can double up to get the two cars going in opposite directions - or just use one.

[knotian]

I built Nico71's mechanism (With CONNECTED drums) and it works well as he has it set up with a SHORT run. When I tried to extend the amount of string on the reels to function on my skip hoist it will not work. Nothing wrong with the design except with a large quantity of 'rope' on the reels, their circumference changes as the rope winds from one to another at will eventually tighten the loop and force a reverse. Nowhere near the length that I need.

So I am back to square one. I need a mechanism where the drums are NOT CONNECTED.

HELP Any other ideas??

 

[Orcman]

Maybe your first idea then is more suitable.  What about having some gears added to the drum that just add resistance to the drop?  Thinking of something like a 24 tooth driving a 8 pinon.  A similar mechanism is used for slow opening hinges.

Don't take this the wrong way, but it sounds like this has a number of problems unique to your MOC, posting pictures will help people get a firm grip on your problem and help you solve it, rather than general hand waving.

[knotian]

If you take Nico's, make the track 36 " long and 60 degrees up you will have it.

http://www.nico71.fr/gbc-tipper-trolley/

[Orcman]

No, what I have is just an idea of what you have.  The more information you give the easier it is to see a solution.

However, Nico's reversing mechanism will still do what I think you need, if you simply put the output from the diff (8 tooth gear) to your original two-drum (on a single axle) approach. 

Providing the skip can drop under it's own weight as the cable is unwound.

How it works: Once one skip reaches the top, it will encounter resistance from being against a stop.  This forces the diff to turn, which reverses the motor.  The other skip now moves up, while the first skip moves down - until the second skip reaches the top.  Once the second skip hits it's stop, it will again forcing the diff to turn. This time in the opposite direction to it did first time. Cycle repeats.

So it's really a reversing mechanism that activates under significant load.

You don't need the second drum to force the movement of the skip, I believe Nico would have only used that because the incline is quite shallow and the skip wouldn't drop under its own weight.

I hope you'll at least post a picture of the completed moc (as payment for my time )

Edited March 1, 2018 by Orcman
more clarity

[doug72]

This is how I used a reversing module and elastic coard to control a single car lift - could be adapted for two cars by using a normal cord between cars over the upper pulley and elastic cord between the two cars and around the lower reversing drive pully.

When cars hit end stops the elastic cord slips until drive is reversed, takes bit of trial & error to get elastic cord tension OK.
Tested for a few hours and performed OK.

Reversing unit is on the right thand side of green baseplate.

Doug

 

[knotian]

Orcman,

What an ijut !!!! I am really embarrassed.

For some knuckle-headed reason. I thought that there would not be enough torque to flip the switch unless I had both drums linked. You were right on with using my original drums. Gravity does bring the skips down, but I put a cable around a bpully from the rear of the skips so one pulls the other down. works like a charm once you get the cars arranged properly on the cables.

Thanks a lot.

[Orcman]

No problems buddy  sometimes we can't see the trees for the forest.

Nice idea with the connecting cable, should keep the skip firmly planted on its track too.

I like Doug's idea too, as it avoids the need for a electrical switch (which can be a be costly).  You could also use a clutch (slipping) gear instead of elastic, or have the timing spot on.

I wanna see pictures (eventually) tho.

[doug72]

7 hours ago, Orcman said:

No

 

7 hours ago, Orcman said:

I like Doug's idea too, You could also use a clutch (slipping) gear instead of elastic, or have the timing spot on.

Tried a white clutch gear but it requires a lot of force before it slips and module pulled apart !

With elastic cord the degree of friction is easy to adjust, and the dwell time at top and bottom is set by gearing on the reversing unit. Also other outputs from reversing unit can run other GBC modules.

 

[knotian]

A further note on the mechanism. I built two and one would work and the other would not. Finally figured out that the problem was lack of torque to 'flip the switch'. Using a large motor solved the problem.

Thanks y'all