Optimizing Motor Pulley & Rope Combination for High Speed

[Prabhjyot Singh]

Hello Guys,
I need little help currently I am working with on a Project that includes Motor Pulley and rope combination. The previous version of our Test bench was having a Motor pulley and rope and the rope was wrapped around the pulley as in most of the cases, but now I am trying to optimize it and want have two wraps of rope around the pulley (as shown in the photo). The pulley will rotate with 70 km/h speed. I just need your suggestions what steps can I take to avoide the overlapping of rope during rotating and which angle should I use between the wraps to get optimium results. During the whole process of rotating the rope will be under tension. Any suggestions will be greatly appreciated. Thankx in advance.

 

[Danger]

You could use some type of physical separation system such as a couple of eyelets just outside of the pulley to maintain the proper orientation.

 

[Prabhjyot Singh]

Hi first of all thank you for your reply. Can you please explain me what you exactly mean by eyelets?

 

[Danger]

In this case, for simplicity and low cost, I was specifically thinking of "eyelet bolts" screwed into a chunk of 2x4 or similar. An eyelet bolt is essentially a "lag bolt" that has the head cut off and is bent around into a shape like a question mark but closed all the way back to the stem. Another example of eyelets are the line guides on a fishing rod.

 

[Prabhjyot Singh]

Ok I think its a good idea will surely think about it. Thankx a lot for your time and reply. I really appreciate that

 

[Danger]

No worries, mate. Let me know how it works out. If there are problems, I have a couple of other ideas that are a bit more elaborate and expensive.

 

[Dr.D]

The pulley will rotate with 70 km/h speed.

What does this mean? The units are for linear motion, but it looks like the pulley just rotates.

 

[Danger]

What does this mean? The units are for linear motion, but it looks like the pulley just rotates.

You have a Doctorate and can't understand what he means? It's obvious to me. Jeez! I never finished high-school, but at least I'm trying.

 

[Dr.D]

It's obvious to me. Jeez!

Since it is obvious to you, why didn't you answer my question?

 

[Danger]

Uh... because you didn't ask it of me. When you don't specifically address a statement, it is assumed to be directed to the OP unless the context specifies otherwise.
As to the answer... unless he is using some really weird kind of translator, the reference is to the linear speed of the rope outside of the pulley radius.

 

[russ_watters]

If a single pulley doesn't generate enough torque, the typical answer is to use multiple pulleys and belts, not wrap the belt around the pulley multiple times. When you wrap the belt, it has to slide on the pulley to stay in the center, so it will wear faster and is prone to binding.

 

[Danger]

If a single pulley doesn't generate enough torque, the typical answer is to use multiple pulleys and belts, not wrap the belt around the pulley multiple times. When you wrap the belt, it has to slide on the pulley to stay in the center, so it will wear faster and is prone to binding.

I might in fact be mistaken about this, but I think that he is using the wraps as in a donkey engine, to provide enough friction that the pulley can positively displace the rope. He does specify that it's a "Motor Pulley", not an idler or "leverage" device.

 

[Prabhjyot Singh]

I am not going to use any belt. I am using a rope used for "Diving" purpose, which is capable of lifting 600 kgs and multiple pulleys is not the answer as there is no space in our test bench for extra pulleys. So I have to use only one Pulley and increase the area of friction, to avoide slippage.

 

[russ_watters]

I might in fact be mistaken about this, but I think that he is using the wraps as in a donkey engine, to provide enough friction that the pulley can positively displace the rope. He does specify that it's a "Motor Pulley", not an idler or "leverage" device.

Yes, that's the way I read it.

 

[russ_watters]

I am not going to use any belt. I am using a rope used for "Diving" purpose, which is capable of lifting 600 kgs and multiple pulleys is not the answer as there is no space in our test bench for extra pulleys. So I have to use only one Pulley and increase the area of friction, to avoide slippage.

Rope/belt/whatever. I was just pointing out that it has to slide on the pulley to stay centered. If that's ok, so be it.

 

[Prabhjyot Singh]

Hi Danger,
I think your idea of eyelet Bolt won't work. Because when I will attach it on the pulley surace and as the pulley will rotate it will also destroy the shape of the rope. So I think it will work in opposite way rather that maintaing the rope in position. As shown in the picture, if I add eyelet bolt on the black spots and when the pulley will rotate it will come in between the rope shape. The rope is 200 meters long, one end of which is connected to a horizontal platform and other end after traveling around another pulley at other end will attach to the second end of horizontal platform that will move 80 kgs of weight with 70 km/h, so my only and primary goal is the rope should remain in this position through out the function..

 

[Danger]

Because when I will attach it on the pulley surace

No! No, no, no, no, no!
The eyelets are supposed to go where the arrowhead from your "Rope" label is, one for each blue line.

 

[Prabhjyot Singh]

aaaaahhhh ok I understood now. Thankx a lot buddy

 

[Danger]

No sweat.

Let me know how it works out. As I said before, there are more advanced methods if necessary.

 

[Prabhjyot Singh]

Ya I am working on it. But seriously telling I doubt either this thing will work with that high speed and weight. I am not that much convinced. Do you think it will hold the position at that hight speed and weight?

 

[Danger]

I honestly don't know enough about it to answer. Even if I knew all of the relevant factors, which haven't been provided, I don't have the expertise to definitively help you. Sorry. I can get into more elaborate mechanical stuff, but not math. Sorry.

 

[Prabhjyot Singh]

Hey hi danger,
Here I am again we constructed the thing n tried to rotate at high speed but the rope overlaps each other at high speed even if we use eyelets. I am thinking a lot about other concepts but m not getting anything can you please help me. Do u have another idea regarding the concept. Pls help

 

[dragoneyes001]

the speed and tension are going to keep making this fail. the rope doesn't have time to self correct before the spinning locks up an errant position.
my only idea would be slip guides which is another form of the eyelets approach.
with a polypropylene wedge forcing the rope to go sideways on the pulley at the point where it needs to kick over with a bar with polypropylene pads between the two in and outbound ropes on the front end of the pulley may keep it from overlapping .the wedge as the bar are solid mounted off the pulley.

 

[Prabhjyot Singh]

Hi dragoneyes001 thankx for your reply.
Can you please explain me what you mean by slip guides? a photo or something like that please

 

[dragoneyes001]

Hi dragoneyes001 thankx for your reply.
Can you please explain me what you mean by slip guides? a photo or something like that please

i'll post something a bit later as soon as i can.

 

[dragoneyes001]

something like this should help guide the rope its possible you might need 2 wedges to really keep it from overlapping:

 

[Dennis C]

I am sure budget is a factor and not sure how the driven side is attached but they do sell multi groove sheaves. We use them for belts and wire rope. If you use an external guide you will need a very soft material that will wear and be replaceable so as not to wear the rope. IE: Motorcycle chains use Teflon blocks as a consumable for a guide.

 

[dragoneyes001]

yeah Teflon would be the best plastic block for the friction points.I suggested polypropylene because its a self lubricating plastic but it may be too soft for high wear.

the multi groove wouldn't work for this application because the rope is being wrapped around the pulley twice the multi is for more belts which only go around once each.

 

[Dennis C]

If the rope is being wrapped around multiple times as a single strand, how is the rope connected to itself?

That's why I asked about the other end. If it is anchored to something on the other end he can use multiple ropes

 

[dragoneyes001]

not sure how it runs i get the impression it is one big rope loop because he has it turning at 70rpm which would chew up a lot of single way rope. actually i think i might have a better idea all together to solve this.
switch back to one loop and use a small spring loaded wheel to increase the ropes pressure against the pulley should remove most if not all slippage unless the rope is lifting stuff then it'd be best to use a block and tackle approach.

 

[Dennis C]

If it is "one big rope loop" running between two sheaves, why not use a belt?

 

[dragoneyes001]

sorry according to the original post they have it running at 70 mph not 70 rpm

 

[Dennis C]

Actually it is 70 km/hr. which is about 43.5 m/hr.