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sprocket vs gear box
3

sprocket vs gear box

sprocket vs gear box

(OP)
The reduction ratio needed im our application is 1800.
Following are the ways to do it:

1. Use an AC invertor and bring its speed down to 140rpm. Then use worm reducing gear 60:1 ratio. Then use a sprocket to reduce the speed further by 4.5 ratio to get a final rpm of 0.5 rpm. The motor chosen is 865rpm
2. Use a 1740 rpm motor and use 2 sets of sprocket reduction to get 0.5 rpm and an ac invertor.
3. Use a double reduction worm gear and 865 rpm motor to get the final rpm to 0.5 rpm

Which of the above 3 is the best choice. The output torque required is 16000in-lb at 0.5rpm. Please suggest a choice from the above 3 or any other choice. The motor only runs few seconds only to rotate a dumper manually. So there is no heat problem. Please help.

RE: sprocket vs gear box

Does the dumper need to rotate 360 degrees or less?

Try a hydraulic rotary actuator.
http://www.helac.com/actuators/quickguide.asp

Or a hydraulic cylinder.

Then use a small motor and small pump to drive the slow speed movement.

Ted

RE: sprocket vs gear box

3
Sounds like 0.5 rpm is your goal.  Can't you just use an ordinary 1725 rpm induction motor with a worm gear box?  Hub City has standard helical worm gear boxes with a ratio of 3460:1 and horsepowers from 1/4 Hp up to 23 Hp.

Don
Kansas City

RE: sprocket vs gear box

I like option 1, with a 4.5 to 1 spur mesh, followed by a 60:1 worm.  

RE: sprocket vs gear box

(OP)
Matt51- It is actually 60:1 worm gear and then sprocket. The main question was whether the sprocket transmits effeciently or worm gear. The dumper has to rotate 360 degree.

Second question is what is the moment of inertia of a 4000lb cuboid with the axis of rotation offest by x inches.
Will the torque required is same if the axis of rotation is x, y or z axis. The cuboid is the cage which tilts/rotates 360 degree. I need the dumper to accelerate from 0 to 0.5 rpm in 3 seconds.

RE: sprocket vs gear box

(OP)
May I ask Matt why he likes option 1?

RE: sprocket vs gear box

Hi,
I like the idea of using as little mechanical reduction as possible, and I like to avoid chains.    

RE: sprocket vs gear box

(OP)
The chain is still used in option 1?

 

RE: sprocket vs gear box

I was proposing modifying option 1. It looks like you have a number of choices.  

RE: sprocket vs gear box

Quote:

The main question was whether the sprocket transmits efficiently or worm gear.
In my view a worm gear is the most inefficient, and it gets more inefficient as the input speed decreases.

RE: sprocket vs gear box

(OP)
I agree with Peter. Thanks.

What about AC Invertor? Is it a good idea to use it to reduce the speed by 1/6?

RE: sprocket vs gear box

I beleive the main reason for the expense of an AC invertor is for it's variable speed capabilities. I have often seen variable speed drives used in place of engineering, as the user could not easily calculate the speed needed. The drives are started up, the correct speed is found, and then the speed is never changed for the rest of it's service life. What a waste of the extra money for the vari-speed drive. If you want to vary the speed, get an invertor, and a gearmotor, and choose your gear ratio to attain your absoulte maximum speed. If you do not need var-speed, just get the gearmotor. You did not mention how this needs to be connected to the machine. You may need a chain drive or dirct coupling to the driven shaft. Does it require overload protection? Many more things to be considered.

Russell Giuliano
 

RE: sprocket vs gear box

You're overcomplicating this.  You're worried about the efficiency of something turning at 0.5 rpm, which should take no more than a little 1/4 hp motor.  The acceleration torque would be minuscule...and there's nothing efficient about a VFD, believe me.

Unless you need variable speed, you should just run the motor at its full rated rpm, gear it down and be done with it.
 
Don

RE: sprocket vs gear box

I agree with Don above.  This is an intermittent operation.  Look at minimizing your first costs because it will take a long time to re-coup energy savings with occasional use.

RE: sprocket vs gear box

(OP)
Russell: How did you calculate the horsepower please?

Don: I calculated the torque to be 16000in-lb by using the formula:

Torque = mass moment of Inertia * ang. acceleration

Inertia =1/12* mass* (sq. of a + sq. of b) where a and b are the sides of the basket.

The I calculated Horsepower using the formula:
 Torque = 5250 * hp/rpm

After I know the torque I can select a gear motor, sprocket or double reducing worm gear. This is why i was asking what is the best choice.
If I just choose a worm gear or sprocket, then I have to use a coupling or chain respectively. What is the easier option in a coupling or chain and sprocket?

RE: sprocket vs gear box

I was assuming that your torque figure was correct.  I got the approximate hp (neglecting efficiency) from:

P = Tw (Power is torque x angular velocity)

P = (16000 #-in)*(0.5 rev/min)*(1 min/60 sec)*(2*pi rad/rev)*(1 ft/12 in)*(1 hp/550 ft-lb) = 0.127 hp

Don
Kansas City

 

RE: sprocket vs gear box

(OP)
Don: Is my torque calculations right?
Assuming the basket is 34" high and 40" wide. Assume the mass of the full basket is 4000lb?

RE: sprocket vs gear box

A fully-loaded basket may not always be the worst-case torque.  I have seen instances when an empty, or partially loaded, container required more torque to rotate.  

RE: sprocket vs gear box

What is the location of the trunnion?  Is it at the center of the rectangular ends?  Also, what is the substance being dumped?

In addition to the torque caused by the inertial reaction (angular acceleration) you need to consider what torque the contents might cause at different levels of fullness as you tip.  Depending on the substance you are dumping, there could be a considerable torque at different fill levels and angles of tip.  

A particulate solid, like sand, would only spill at an "angle of repose" so that more sand would end up on one side of your pivot point and its weight would cause a torque.  A non-viscous liquid, like water, would be self-levelling, but depending on the shape of the tub and the location of the trunnion, it could still cause a torque.  If your pivot was down at the bottom of the bucket, for example, you could have a hefty torque as you tip the entire 4000-lb load!

Don
Kansas City

RE: sprocket vs gear box

(OP)
The flat disc brakes are dumped. The  inside dimensions of the cage are 38" high x 42" long. The parts basket which is placed inside is 34" high x 40" long. I am only giving two sides because the 3rd side is not important as it won't be used in the calculations. The basket has 4" high feet.

The axis of rotation is exactly 19" i.e. centre of the cage.
I just wanna verify my calculations if the part has 4000lbs and it is full. What will be the torque required to rotate it at 0.5rpm in 3s?

RE: sprocket vs gear box

You may want to consider if the "load" is going over center, a system that will not allow the dumper to speed up.  I'd prefer hydraulics over anything that has a chain.  I can put a fuselink in the system to eliminate  a run-away synerio.
Just my opinion.
Ray

Every once in  a while the voices in my head have good ideas.

RE: sprocket vs gear box

Wow! This gets overcomplicated when asking a room full of engineers> From economic standpoint, I would buy a 1/4HP 1800:1 ratio gearmotor from Hub City, Ohio, Boston or other mfgr then use a sprocket on the gearbox output, getting to your final driven ratio. Direct coupling is more difficult to align, and the final sprocket drive will give you more options for mounting.

This type of question is why there USED TO BE local distributors. A little bit of engineering background with vast product knowledge, to custom tailor the application to the customer, creating the most efficient drive, both in energy usage and initial equipment and operating costs. This commodity has been replaced by your big catalog, and figure it out for yourself

Russell Giuliano
 

RE: sprocket vs gear box

(OP)
Let me ask this: if we have a worm gear box and a motor with 2hp attached to it how much hp and torque we loose from the motor to the gearbox motor due to the effeciency of the gearbox?
The question I am trying to get an answer is how do you calculate torque. Please read this thread and answer the question. I donot think I can put this question in bold font otherwise I will.
Russell: What type of gears will the gearmotor have: worm gear, I assume?  

RE: sprocket vs gear box

At 0.5 rpm, the moment of inertia is less important than the eccentricity of the load.

If you had a 4000 lb weight with its center located 19" away from the axis of rotation, then the worst case torque required to start rotating it would be the product of those two numbers, i.e.

T = W x r = 4000 lb x 19 in = 76000 in-lb = 6333 ft-lb

Which is pretty substantial.  Maybe I'm misunderstanding the problem.  

If you've got a rectangular basket that may be completely or partially full of heavy awkward stuff, you can't assume that it will be, or stay, uniformly distributed throughout the available volume.  One bad case would be when it's all jammed up on one side, or worse, in a corner... in which case, assuming that it's all at the edge of the basket is not all that unreasonable.

Of course, it can all spontaneously fall to the other side of the basket, giving you an overrunning torque just as large as the starting torque.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: sprocket vs gear box

Harrinshotmail, according to a worm gear manufacturer's data a typical design can have efficiency in a range 0.4-0.91 and low values are for high ratios. It means even as much as 60% of the transmitted power could be turned into heat in the worm gear. If you want high efficiency and high ratio and still compact design then you should go for the modified epicyclic gear, but they probably don't sell them  off the shelf, so it only makes sense if you want to produce a whole number of this stuff of yours.

RE: sprocket vs gear box

(OP)
WE cannot use your formula in this case because the load is not offset by 19".The center of gravity and the center of rotation are almost same.  It may be only 1" to 2" out. So 4000 x 2" = 8000 in-lb or 666lb-ft.

I donot think we can ignore the inertia in this case.If the weight of the basket is 4000lbs.

T = 4000/12 x (40x40 + 34x34)x 0.017rad/sq.sec = 15617 in-lb i.e.131lb-ft(you can see that this is double). In calculating  Inertia we can add to the inertia the square of the offset distance with the load, I mean, 4000x2x2=16000lb-sq.in and the new value of torque will be 1324 lb-ft

Since T =Inertia x angular acc.

Assuming t= 3s N=0.5 rpm ang acc will be 0.017 rad/sq.sec

i totally understand the load will be shifting but the weight will be decreasing as we will be emptying the basket too.

2nd question repeated: if we have a worm gear box and a motor with 2hp attached to it how much hp and torque we loose from the motor to the gearbox motor due to the effeciency of the gearbox? I'll give an example:
If u have a 2 hp motor connected to a worm gear box at 1740 rpm the torque will be 72in-lb. Now what will be the value of hp and torque at the other end of worm gear if it is  60:1 ratio and the effeciency is 35%.

Please see the picture of the dumper
 

RE: sprocket vs gear box

Oh brother!  Tell me that's not made out of 80/20!

My car doesn't even weigh 4000 lbs!  Are you sure that slotted-aluminum contraption with little bearings will even support the weight?  

I think I'm going to run away from this one.

Don
Kansas City

RE: sprocket vs gear box

As hydtools originally suggested; I would look at doing this simple job with a simple single hydraulic ram & rotating arm arrangement. You would end up with, simple to design, both speed and proximity controls. As an example, look at how a skip bin type garbage truck does the job of rotating the bin and get some ideas from that.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
 

RE: sprocket vs gear box

I'm sorry, I've just read one of your responses where you mention the requirment for 360deg rotation. Perhaps a ram may not do what you require.
Why is the full rotation required?

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
 

RE: sprocket vs gear box

A ram could do the job if you use a rack & pinion arrangement. The rack would be attached to the ram imparting motion to the bin via the pinion. This would give you full rotation but may not suit your application as it would require cycling of the ram to the return position.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
 

RE: sprocket vs gear box

(OP)
For Don:I have this equipment running for 10years.

I donot need 360 degree but atleast 270 deg. This we we can insure that there are no parts left inside.

I just need to order few more.so I am looking for best possible way to design the same thing. I need to know what are the different possible ways to achieve this- with worm gear, AC drives, sprocket, may be all of them but what is the best way to achieve the rpm and torque.  

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