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Braking of a spinning disc
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Source：Internet Author：Unknow Pubdate：2010-06-25
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jimsmiff (Mechanical)
16 Jun 10 7:28
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. 字串4
Any help is greatly appreciated,
Regards
Jim
MacGyverS2000 (Electrical)
16 Jun 10 7:51
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 (Automotive)
16 Jun 10 8:32
what he said, but have a look at the following Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? - http://files.engineering.com/getfile.aspx?folder=4e694235-f791-4482-b683-61
GregLocock (Automotive)
16 Jun 10 8:36
Sorry, there's an error of 2 pi in there, should be 112 Nm Cheers 字串9
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
LionelHutz (Electrical)
16 Jun 10 8:42
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 (Mechanical)
16 Jun 10 13:16
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} 字串4
Although, I am a fan of the pokes.
Fe
MacGyverS2000 (Electrical)
16 Jun 10 14:37
Fe,
Considering the working title for these fora is "INTELLIGENT WORK FORUMS FOR ENGINEERING PROFESSIONALS", anyone that wants to last more than a few posts had best be able to at least appear to be an engineer.
I've managed to fool 'em for this long Dan - Owner
http://www.Hi-TecDesigns.com
FeX32 (Mechanical)
17 Jun 10 1:03
lol. Good one Dan. At first that flashing pic of yours through me off , but be sure you are one of those 10-15 that I respect.
I guess the 'poking' is a sort of natural selection mechanism. The ones being poked will get pi$$ed and leave for good, leaving only those that are poke free
Fe
rmw (Mechanical)
19 Jun 10 17:13
字串6
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. 字串4
rmw
jimsmiff (Mechanical)
21 Jun 10 7:56
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 (Publican)
21 Jun 10 10:19
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: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm 字串7
for site rules
MacGyverS2000 (Electrical)
21 Jun 10 15:03
Quote (GregLocock):Sorry, there's an error of 2 pi in there, should be 112 Nm
Quote (jimsmiff):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 (Aerospace)
21 Jun 10 15:40
Sure, I'll bite; I get 2.63 N-m
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
IRstuff (Aerospace)
21 Jun 10 15:42
Oops, forgot to attach the files 字串7
http://files.engineering.com/getfile.aspx?folder=0829051c-3795-4b54-981e-16f5b082681d&file=diskbrake.mcd
http://files.engineering.com/getfile.aspx?folder=39d7aae3-bd61-4048-96c8-2a228a85ba3c&file=diskbrake.pdf TTFN
FAQ731-376: Eng-Tips.com Forum Policies
GregLocock (Automotive)
21 Jun 10 19:14
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: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
YvesLLewelyn (Mechanical)
21 Jun 10 23:00
字串2
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 (Aerospace)
22 Jun 10 1:33
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: Eng-Tips.com Forum Policies
321GO (Automotive)
23 Jun 10 4:49
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.
字串9
patprimmer (Publican)
23 Jun 10 5:55
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: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
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