3hp shaft design challenge 2

[bluduc]

Hi guys/gals,

First post. Hope it is in the right category... this should be fun.

Given:
I need to design a drive shaft to transmit 3hp at 400rpm. It is 70" long and supported by bearings at each end with flex couplings- assume no induced moment. It has a simple 15lb lateral load right in the middle of the shaft. I'll make about 300 of these per year.

Question:
What is the least expensive construction for this shaft? Diameter, cross section, material, and manufacturing method are all undefined: go nuts.


Looking forward to your thoughts!

Happy 2013!

 

[desertfox]

Hi bluduc

Who as set this challenge for you to design a drive shaft?
Can you give more details about the supporting bearings and possibly a sketch of what you have so far?

 

[bluduc]

DF,

This is something I am toiling with at work, but I can't define "work" further. I'm not sure why that is relevant. Does your interest in a challenge depend on its source?

I could give more details, but I don't want to taint/constrain/contaminate anyone's thinking. This is a new product, and I can design the bearings, couplings, etc to mate with the shaft. I listed the only fixed variables (length, power, speed, loads). The remaining variables are open to innovative ideas to get the shaft constructed at quantity as inexpensively as possible.

Hope this helps.

 

[dvd]

What is the P.O. number?

 

[MikeHalloran]

First thing that came to mind is a length of music wire. ... which might be contraindicated for windup, and could add some interesting dynamics, depending on the nature of the central load and how it's attached or borne.

Second thing that came to mind is a paper tube. Like from a roll of paper towels, but larger, longer and stronger. Many roll goods, like carpeting and plastic film, are delivered on such 'roll cores', which might be available for the cost of hauling them away, depending on where you are.



Mike Halloran
Pembroke Pines, FL, USA

 

[bluduc]

DVD, GC: As if zero topics or advice on this forum ever relate to one's work.

Does anyone have input? Or am I ostracized for discussing a matter from the office?

 

[gearcutter]

Well if you aren't willing to help us so as we can help you.....................
As MikeHalloran says.
Along with piano wire or a paper roll; you could also try a length of recycled timber.
All these would be amongst your cheapest options.



Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[dvd]

My opinion of what constitutes a humble request for help is to provide information on what has been tried and some explanation of why it is causing one difficulty. This question appears to be asking for an engineering study.

A general guideline that helps me in the shaft design area is to keep deflections to a minimum and not use materials with really high yield stress since the deflections are driven by Young's modulus, not stress. I would also recommend to look at the resonant frequency of this gizmo, since it seems to have a fairly long span between bearings.

 

[berkshire]

You also need to give the prime mover, electric motor, internal combustion engine, wind turbine?
B.E.

 

[Tmoose]

In addition to the questions posed by others -
operating 24/7 ? Indoors or out? Acceptable Service life?

Depending what the drive and driven devices are on the "other" sides of the couplings, if radially stiff couplings are used ( U-joints, disc pack) the support bearings might be eliminated. Creating "proper" bearing seats on a shaft is a significant task. As is aligning the drive and driven components and the structure(s) that would support the support bearings.

Maybe eliminate the support bearings and put the money towards something like this?

http://www.tractorsupply.com/replac...eZip=01886&ddkey=http:LocationBasedPricingCmd

 

[electricpete]

This is something I am toiling with at work, but I can't define "work" further. I'm not sure why that is relevant. Does your interest in a challenge depend on its source?

1 - It would if it were a post for school.
2 - There may be some details of the application which you don't consider relevant which actually are (that's why we all ask questions... we don't know all the answers). A general idea helps.

Those are valid reasons for asking the question imo. I understand also there can be many valid reasons for not sharing all details.

=====================================
(2B)+(2B)' ?

 

[hydtools]

Does the load rotate with the shaft or does it remain in one direction, down for example? How is the load attached/applied to the shaft? Is shaft deflection at the load permitted? Hard start or soft start? Is corrosion a concern?

Ted

 

[Metalguy]

Perhaps the school issue has scared him away?

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[dvd]

I am guessing there is a connection somehow:

http://www.bluduc.com/

 

[bluduc]

Hey guys/gals(?)... thanks for the replies.

DVD: No, this is not for my side-consultancy. It is for my day job. And to your 'engineering study' comment... I am not interested in an engineering study so much as I am interested in ideas TO study. I'm so early in the conceptualization, I want to pull together all options before I start evaluating which is optimal. Ideation outside our normal group is all I need; not hard answers.

Metalguy and Electricpete: School is in my rearview, and I never want to return. 'Doing' is better learning.

MikeH: Thank you, that is in the spirit of why I came here: outside the box suggestions to brainstorm a simple torque transmission problem. The cardboard tube is a pretty good idea- I'll run with it for a bit.

GC: The timber idea is also a decent idea. Straightness and lateral stiffness might prevent its use, but that's a good thought.

Hyd: Those are good questions. The load rotates with the shaft. I really can't say what it is, as the nature of my devel cannot be shared. But I can say lateral stiffness of the shaft is important. As is corrosion/contact/environment. But again, I can't share what that is.

Maybe I'll rephrase the premise of the discussion as I can't share enough details to adequately frame the current question. Discussion rephrase:

Open to material suggestions for a shaft 6' long which needs to handle a high degree of rotational power and lateral loading relative to its aspect ratio. The shaft needs to cost less than $20 at 300 annual quantity. What is the first thing that comes to your head?

 

[MikeHalloran]

Low- budget filament winding or tape winding comes to mind, as in resin and fiberglass tape over a paper tube core rotated in a modified or homemade lathe. Since you only need 1.5 units per working day, it doesn't have to go real fast. A PLC should be able to run it unattended after startup.

Mike Halloran
Pembroke Pines, FL, USA

 

[bluduc]

Mike that was helpful- thanks! We don't do any manufacturing in house- it is all contracted, but yes, good thought.

 

[dvd]

If the shaft transmits 3 HP at 400 RPM, then the transmitted torque is about 473 lb-in. Is the 15 lb lateral load at mid-span the point at which the torque is removed, and if so, what is the component that removes the torque: a gear, sprocket, pulley, friction, etc.? I calculate a moment-arm of nearly 31.5 inches, to get a 15 lb force at that torque. Surely a component with that much geometry weighs something. A better idea of what the mechanism is actually doing would be necessary to get very far with this.

 

[Tmoose]

http://www.lowes.com/pd_72713-1792-101550_0__?firstReferURL=http://

http://www.lowes.com/pd_72713-1792-...iew&findStoreErrorURL=StoreLocatorDisplayView

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