Mark Allanson
|
| posted on 17/2/04 at 08:34 PM |
|
|
Self balancing props?
There seems to be a lot of chat about props at the moment, and I had another little thought (oh! no I hear!!)
You can get anti punctue goo to go in motorbike tyres which naturally balance the tryes as well bu the goo being centrafuged out onto the trye inner
face.
Could you put 1/2 a pint of heavy grade oil inside a prop to make it auto balanced?
Just another zany thought............
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
|
|
|
|
|
Viper
|
| posted on 17/2/04 at 08:40 PM |
|
|
So what would happen when you had been parked up fpr a while? wouldn't all the oil end up in the bottom of the prop? so when you pull away it
would be chronicaly out of balance untill such time as the oil spreads out?
just a thought..
Tim
|
|
|
blueshift
|
| posted on 17/2/04 at 08:55 PM |
|
|
yeah, it would only take a few revolutions to balance itself though, and those would be at low speed.
Sounds like a pretty cool idea to me. I suppose you'd want to do it in a little section or have some fairly serious baffling, to avoid surge.
hmm.. I wonder if hard acceleration would cause it to go out of balance due to surge..
think I'll let someone else test it 
|
|
|
Viper
|
| posted on 17/2/04 at 09:03 PM |
|
|
Still think a Jubilee clip would be a lot easier...
|
|
|
200mph
|
| posted on 17/2/04 at 09:04 PM |
|
|
I think the centripetal force acting on the oil (perhaps 200g) would take care of surge due to acceleration (2g?)
however, i think this is inherently a bad idea, and not something I would be willing to try.
but thats just me
Mark
edit: just thought, thats making the bold assumption that the prop is horizontal. As most props aren't, the oil would get to the bottom of the
prop with no way of gettin back up.
Bad idea methinks
Mark
[Edited on 17/2/04 by 9904169]
|
|
|
Peteff
|
| posted on 18/2/04 at 04:48 PM |
|
|
How will it work?
I can't see how it can balance the prop, only the oil inside it will be balanced by the rotational forces unless there are surface imperfections
inside the tube which are filled by the oil.
yours, Pete.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
|
|
|
Jon Ison
|
| posted on 18/2/04 at 04:53 PM |
|
|
ditto, jubilee clip.......
|
|
|
Mark Allanson
|
| posted on 18/2/04 at 08:42 PM |
|
|
I'm not going to try it, I just wondered if it would work. I don't understand the principles involved in the bike tyre stuff, but wondered
if it would translate to a prop.
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
|
|
|
Simon
|
| posted on 19/2/04 at 01:33 AM |
|
|
Mark
Not being a physicist or anything, my guess as to how the bike goo works, is exactly the same principle as any liquid.
It will always find its own level (and therefore balance) - ie flat, it's just that the centripetal force generated by the rotation of the
wheel/tyre gives a round "flat" surface, if you see what I mean.
I think you'll find that the goo won't spread up tyre sidewalls, other than any natural miniscus the goo has (which under the rotational
forces involved may well increase (based on the assumption that the goo in the middle of the tyre (around centreline) is deeper, and subject to higher
g's (moving faster) - unless someone could correct me (could be a constant as shallower goo going round a tighter bend (in which case this para
is utter nonsense))
ATB
Simon
|
|
|
Spyderman
|
| posted on 19/2/04 at 11:48 AM |
|
|
Any "goo" or liquid/semi liquid will only ever balance itself out assuming it has a perfectly smooth symetrical surface to flow on. It
cannot balance any inperfections in the tyre.
To simplify let's assume that on this particular tyre the imbalance is due to a small lump of rubber on the inside of the tyre. The tyre inner
profile is square to simplify.
We pour the "goo" into the tyre and rotate to disperse it. This creates a nice even coating over the inside and covers up the lump. In
order for the tyre to be in balance now requires that the "goo has the same Specific Gravity (sg) as the rubber. If it is lower then the tyre is
still out of balance (albeit to a lesser degree), or if it is higher the the tyre is still out of balance as it has a light spot.
Now let's assume that the lump causing the imbalance is on the sidewall. Depending on how high up the sidewall it is would require lots of the
"goo" to reach it therby virtually filling the tryre with liquid (and extra weight) which would not compress.
Now let's assume that the imbalance is due to an external lump or even due to the valve. How can anything on the inside possibly balance what is
happening on the outside?
Also if a wheel is already out of balance then adding extra mass can only increase that imbalance as the tyre rotates. The vibration caused is as a
result of the heavier part of the tyre trying to scribe a larger arc and this amplifies due to the extra "goo" being spun out to the
heavier section.
You can all wake up now!
Terry
Spyderman
|
|
|
200mph
|
| posted on 19/2/04 at 12:10 PM |
|
|
quote:
Originally posted by Spyderman
Any "goo" or liquid/semi liquid will only ever balance itself out assuming it has a perfectly smooth symetrical surface to flow on. It
cannot balance any inperfections in the tyre.
thats not strictly true.
in the same way that gravity will pull liquid concrete into a flat surface no matter what it is poured onto (ie undulating ground) the same would be
true of a liquid inside a rotating tyre/tube.
The liquid would spread itself into a uniform surface as long as the force was applied to it. The molecules at the bottom will be experiencing a
higher centripetal force than those at the top, keeping them in their relative positions.
well, thats the way I see it. 
Mark
|
|
|
flak monkey
|
| posted on 19/2/04 at 12:40 PM |
|
|
I think what spyderman means is that the liquid will form a flat surface on the inner surface of the tyre. But it will not balance the tyre!
The surface will be of different densities around the tyre, so the amount by which it is out of balance will remain the same.
Plus if the if the tyre is not concentric then more 'goo' will collect in the more offset place on the tyre, making it even more out of
balance! This is since... centripetal (centrifugal whatever) force = mrw^2. w remains constant for any diameter since it is not dependant on a
distance (rads/s). The mass is constant, so as the radius increases the force increases. More force = more 'goo' in that position on the
tyre, making it more out of balance.
Well thats what i think anyway!
And it probably makes no sense at all!
Cheers
EDIT: w is the angular velocity of the propshaft measured in radians/second.
[Edited on 19/2/04 by flak monkey]
[Edited on 19/2/04 by flak monkey]
Sera
http://www.motosera.com
|
|
|
200mph
|
| posted on 19/2/04 at 02:00 PM |
|
|
w being?
|
|
|
GO
|
| posted on 19/2/04 at 02:52 PM |
|
|
must me some kind of velocity
|
|
|
Terrapin_racing
|
| posted on 19/2/04 at 02:59 PM |
|
|
If you get nothing else from reading this page, understand this: An eccentric mass in a variable velocity orbit (an off-center lump that speeds up and
slows down repeatedly in a circular cycle), is a POINT MASS that will interact with BOTH the LINEAR MASS aspect of the frame (it's linear
position/velocity in space), AND the ANGULAR MASS (moment of inertia) of the frame, which describes it's angular position/velocity in
relationship to space.
A mass's linear (point) mass aspect, accelerating in an angular (circular) path, crosses the supposed "barrier" between linear and
angular momentum! AS such, it can become a bridge for us to carry angular (spin) accelerations out into the linear world, and "force
rectify" them to produce external (linear) thrust!
In short, crap idea/won't work
|
|
|
200mph
|
| posted on 19/2/04 at 03:59 PM |
|
|
yeah, I completely agree with both of you, however it has been oversimplified, as one equation isnt sufficient to describe the kinetics of a liquid
inside a rotating object, especially one which solidifies with time....
also, the issues of propshaft and goo inside a tyre are different ones also.
nice idea though
mark
[Edited on 19/2/04 by 9904169]
|
|
|
Chris Leonard
|
| posted on 19/2/04 at 05:15 PM |
|
|
so how do you balance a propshaft at home using jubilee clips then
|
|
|
Viper
|
| posted on 19/2/04 at 05:51 PM |
|
|
a Jubilee clip is simpley a weight that holds itself on......so basicaly you put the jubilee clip around the shaft, with back wheels of the ground,
run it up through the gears, or take it for a drive, if you feel a vibration, rotate the clip and try again, keep trying till you balance out any
vibration, simple.
Tim..
|
|
|
Spyderman
|
| posted on 20/2/04 at 03:18 PM |
|
|
quote:
Originally posted by Viper
a Jubilee clip is simpley a weight that holds itself on......so basicaly you put the jubilee clip around the shaft, with back wheels of the ground,
run it up through the gears, or take it for a drive, if you feel a vibration, rotate the clip and try again, keep trying till you balance out any
vibration, simple.
Tim..
But how do you know which end of propshaft is out of balance or are you just putting it in the middle and hoping for the best?
Spyderman
|
|
|
Viper
|
| posted on 20/2/04 at 05:04 PM |
|
|
It doesn't matter where along the shaft you put it,
Tim
|
|
|
