Braking of a spinning disc

[jimsmiff]

Hi

Hopefully i have put this in the right forum, thinking the application i want is similar to braking an automotive vehicle or similar.

I have a vertical disc of 0.6m Ø weighing about 15 Kg. This has coil loaded onto it (via a ctr spindle) which is pulled off, thus rotating the disc. The coil weighs about 10Kg and the OD is 0.6m Ø. (Obviously this reduces as the coil is unwound but i only want to know the max. worst case value.) The speed of the 'puller' is max 30m/min.

I want to add a brake onto the shaft to stop the spinning disc, time to stop in say 1 sec (i.e emergency situation). How can i work out the torque of the disc to compare with the brake torque values to ensure i spec the right one? Obviously i will approach a supplier for their input, but i would like to try to work it out and understand the maths myself. I dont care about the fact the disc will speed up or the OD of the product will reduce as it is pulled as if the brake can stop in the worst case sceanrio, then all bases should be covered.

Any help is greatly appreciated,

Regards

Jim

 

[MacGyverS2000]

You're a mechanical engineer and you can't calculate the energy in a spinning disk of known weight/size?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[GregLocock]

what he said, but have a look at the following

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[GregLocock]

Sorry, there's an error of 2 pi in there, should be 112 Nm

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[LionelHutz]

Geeze, I'm electrical and don't see how hard it is to do that.

If you know the inertia in lbs-ft and the speed in rpm then the torque in ft-lbs is calculated as

T = Inertia X Speed / (308 x decel time)

At least I think I got that right. I didn' spend to much time on it.

It should be simple to calculate the rotating speed given the circumference and the product take off speed. To calculate a rough inertial this sounds like a couple of cylinders, the disk and the product, so the forula for that is simple too.

 

[FeX32]

ahhh. Well one should start from conservation of angular momentum to ensure understanding (for the OP). (imo, just because someone signs up here doesn't mean they are an engineer, probably most are not) {I have read very informative posts only from a group of about 10-15 posters}
Although, I am a fan of the pokes.


Fe

 

[rmw]

I have got a real engineering degree and a license to go with it but I get "poked" every now and again. We are not infallible either.

That said, I see a lot of threads that ask questions so simplistic to anyone with real engineering knowledge or training that I take the position that if their understanding is at the level of their question, that level of understanding won't allow them to understand an answer that I would give, so I don't get involved.

A lot of good dedicated members got involved once in a thread where it turned out that the poster was a glass blowing artist who wanted to generate power and light the world with the waste heat from his glass furnace. What he wasted was the time of a lot of good engineers who didn't pick up on his level of ignorance and spent a lot of valuable time trying to propose solutions to someone who ended up being incapable of understanding them.

So after I get this rant submitted I think I'll go back up and give Dan a star for his initial answer.

rmw

 

[jimsmiff]

Thanks eveyone for your replies, helpful and not.

Greg thank you though for at least showing me a route to the problem.

I have one question though, and so prepare to open myself to more abuse. You calculated the angular velocity (omega) presumably into rad/m ? I thought SI unit of this should be rad/s...i only seem to be able to get t=1.873Nm

Open to comments

 

[patprimmer]

If you show no respect for other peoples property and rules you really do set yourself up for abuse, especially when also asking them to do valuable work for nothing.



Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[MacGyverS2000]

Sorry, there's an error of 2 pi in there, should be 112 Nm

You calculated the angular velocity (omega) presumably into rad/m ? I thought SI unit of this should be rad/s...i only seem to be able to get t=1.873Nm

Ow ow ow, my head is really starting to hurt now...

Are you freakin' kidding me?!

Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

Sure, I'll bite; I get 2.63 N-m



TTFN

FAQ731-376

 

[IRstuff]

Oops, forgot to attach the files

http://files.engineering.com/getfil...795-4b54-981e-16f5b082681d&file=diskbrake.mcd

http://files.engineering.com/getfil...d61-4048-96c8-2a228a85ba3c&file=diskbrake.pdf

TTFN

FAQ731-376

 

[GregLocock]

oops, I misread 30 m/s not 30 m/min.

So yes IRstuff and I agree, not very much is the answer.

As a comparison, operating a butterfly nut with your thumb and forefinger will generate about that much torque.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[YvesLLewelyn]

I have to put in a few words in support of Smiffy - there is far too many outraged "You're wasting our incredibly valuable time" type of comments on this forum in general. His original question was perfectly reasonable.

 

[IRstuff]

Ah, that explains it, Greg.

That's one of the beauties of using units in Mathcad; it tends to keep things straighter...;-)

TTFN

FAQ731-376

 

[321GO]

Fully agree with YvesLLewelyn.

Maybe that jimsmiff is not an engineer, i don't know and i don't care. I still have respect for his willingness to learn and improve on a personal level.

Why the whining? Replying is not manditory i believe.

 

[patprimmer]

Yves & 321go

I notice neither has really served this community all that much, but you feel you have the right to tell long serving very active members who contribute a lot that they should support the breaking of site rules.

The rules are for a reason. Those reasons should be obvious.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules