peterriley2
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 posted on 11/7/06 at 10:28 PM |
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physacists?? centrifugal forces
im hoping one of you guys is some sort of physacist and knows the answer to my predicament. i wanted to know if when cornering with a trailer,
concidering that centrifugal forces are acting, does the weight of the trailer get any heavier? might be a very stupid question but i need to make
sure- i am making a small caravan (the teardrop if anyone saw the other posts) and i am in the process of designing the suspension.
if the whole caravan weighs 100kg's, then not concidering the weight in the wheels, the axles-hub joint would only ever experience half that
weight- going in a straight line. on a corner, i guess that the 50kg's from the other wheel is shifted onto it, so it experiences twice that
weight (100kg's). my question was it that all the weight that it would experience, or would centrifugal forces add any weight, and stress the
axle-hub joint any more?
there is nothing to do with aerodynamics and down force here, which will act when its going straight, but the corner question is enough to fry my
brains at the moment.
i hope this is makingsense, re-reading what i have written it seems maybe im being very stupid, id just like to know how and why.
i have included the most basic of drawings, frankly im embarresed at the quality of it, but my tablet's broken at the moment, so i cant do any
better!!
any help/constructive critisism would be very appreciated!
 
Rescued attachment centrifugal.JPG
Joel
If you dont respect yourself, dont expect respect from anyone else
Live your dreams, dont dream your life
Women only want you for one thing- everything!
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owelly
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| posted on 11/7/06 at 10:35 PM |
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I tend to exagerate things to picture things in my head. If you were to corner too fast, then the trailer would tip over. Just before the trailer
tipped up, all of the weight would have been transferred to the outside wheel. Therefore, the trailer would not gain weight but the outside wheel/hub
woul be taking more weight.
I'm ignoring the weight on the drawbar!
[Edited on 11/7/06 by owelly]
http://www.ppcmag.co.uk
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Liam
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| posted on 11/7/06 at 10:43 PM |
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Could centrifugal force apply downforce? Can't see it myself, as centrifugal force is acting purely sideways. The fact that it rarely acts
through a vehicles roll centre and therefore causes it to roll on its suspension can only redistribute the vehicles weight over it's axles - it
can't add to that weight.
A single wheel of your trailer is very unlikely to even see the full 100kg unless you intend to corner fast enough to flip it over! And that's
assuming there's even enough grip/high enough cog for that to happen - it might just slide.
Liam
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3GEComponents
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| posted on 11/7/06 at 11:05 PM |
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Caravan?
The curse of motoring!
Where's the fun in peeing in a bucket?
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Peteff
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| posted on 11/7/06 at 11:21 PM |
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If you brake in a corner with an unbraked trailer it will try to go straight on and cause the back end of the car to lift which wil be the opposite of
the trailer gaining weight but have the same effect. Jroberts, you've watched too much Clarkson, peeing in a bucket is loads of fun, just
listening to the change in tone as the bucket fills up gives a real sense of achievement  Liam, if you can make this caravan with a weight limit of
100kgs you will be very lucky and if it doesn't push your car when you brake or corner you will be even luckier.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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owelly
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| posted on 12/7/06 at 01:39 AM |
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BTW, that drawing is of the highest standard. It looks like one of mine!!
http://www.ppcmag.co.uk
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britishtrident
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| posted on 12/7/06 at 07:18 AM |
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Stop thinking in terms of weight and think in terms of forces.
For example take a trailler or carvan weighing 1 ton.
As already pointed at max cornering speed you get 100% weight transfer to the outside wheel, we will guess max cornering is at 1G.
In 1g cornering for a trailler weighing 1 ton a reaction force of 10kn is generated in the horizontal direction.
Using vector addition add this to the vertical load (also 10kn) and you get a reaction force of 14 kn acting upwards at 45 degrees from the tyres
point of contact.
[Edited on 12/7/06 by britishtrident]
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Howlor
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| posted on 12/7/06 at 07:44 AM |
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Hi,
Worth over engineering anything in this area. Take a look at the link, this happened on the M62 near me on Monday. Very
unlucky.BBC
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ReMan
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| posted on 12/7/06 at 08:03 AM |
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quote:
Originally posted by britishtrident
Stop thinking in terms of weight and think in terms of forces.
For example take a trailler or carvan weighing 1 ton.
As already pointed at max cornering speed you get 100% weight transfer to the outside wheel, we will guess max cornering is at 1G.
In 1g cornering for a trailler weighing 1 ton a reaction force of 10kn is generated in the horizontal direction.
Using vector addition add this to the vertical load (also 10kn) and you get a reaction force of 14 kn acting upwards at 45 degrees from the tyres
point of contact.
[Edited on 12/7/06 by britishtrident]
So the answer is yes then! 
If you think of the extreme case where the vehicle/trailer was going round a banked corner, or better still a wall of death, then the faster it goes
the "heavier" it will get.
Though obviously a caravan would have tipped over a long time ago.
Can you not use the bolt on indespension units, presumably they are rated with different loadings?
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peterriley2
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| posted on 12/7/06 at 09:42 AM |
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okay ill put a little more explination on, the weight that im aiming for is 100kg's- the pic is of a similar design- mine will be simplified
with carbon fibre for the main body. i cant use indespension units as they aer only really rated at 350kg upwards, and still then they bounce, so on
mine the caravan would be all over the place. the caravan will be towed by my locost, which will mean it will be easier for the back end to lift in a
corner, as the car is so light.
that runaway wheel thing has certainly scared me, i was starting this post in order to see the minimum the axle will hold, i was always going to over-
engineer it anyway.
the suspension i have designed is a mini-moto supension unit, with a sheath over the bottom and top, that than slide over each other with little
friction. they are attached- one to the top of the suspension unit, one to the bottom. the hub is attached to one of these, and the chassis is
attached to the other. i have simplified this a lot, but it was the strength of the attachments to the hub and chassis that i needed to find what
weights/forces would be acting on them, to see how much i would need to strengthen them.
thanks for the help guys, and keep it coming!
Joel
If you dont respect yourself, dont expect respect from anyone else
Live your dreams, dont dream your life
Women only want you for one thing- everything!
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peterriley2
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| posted on 12/7/06 at 09:46 AM |
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pic didnt work
 
Rescued attachment littleguy.jpg
Joel
If you dont respect yourself, dont expect respect from anyone else
Live your dreams, dont dream your life
Women only want you for one thing- everything!
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02GF74
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| posted on 12/7/06 at 10:34 AM |
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quote:
Originally posted by peterriley2
I wanted to know if when cornering with a trailer, considering that centrifugal forces are acting, does the weight of the trailer get any heavier?
What exactly are you asking?
Weight is the force acting downwards due to gravity - and has nothing to do with towing it. Before everyone screems and shouts, when you are towing
in a horizontal direction you are overcoming the resistance to movement since you are not lifting anything upwards. This is how the world's
strongest men are about to pull jumbo jets and such - they are overcoming the rolling resistance of the object.
What I think you are asking are about the forces the trailer is exerting on the prime mover; these will be acceleration - overcoming inertia of the
trailer, braking - momentum of traioer pushing on you when you slow down and cornering forces.
Centripetal force acts radially - think of a stone on end of a string spinning round. Now imagine the trailer is the stone - so what is the string?
It is the trailer tow point and this is keeping the trailer from going off in a straight i.e. it forces the trailer to keeps going in a circle so the
trailler is trying to push the rear end outwards. Also the trailer tyres are keeping the trailer in line - imagine the trailer had no tyre grip or
was floating, it would be at a tangent to your circle of movement.
From memory centripetal force is mv2/r (or something like that) and depends on the mass of the trailer, the heavier a trailer is (i.e. more mass) the
bigger the force it puts on the back end of the car to pull it outwards.
So to answer the question, I don't think the trailer is getting heavier but the force it exerts on the rear will depend on the weight of the
trailer, how fast you are going and the radius of the bend.
some real physicist will now correct me.....
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Marcus
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| posted on 12/7/06 at 11:46 AM |
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quote:
What exactly are you asking?
I think he's getting at designing the suspension on the trailer, not the effect the trailer will have on the car.
The physics sounds good though!
If each hub were designed to take the total load of the caravan (100kg) and then add a 50% safety margin, that should be sufficient (IMHO)
Marcus
Because kits are for girls!!
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Confused but excited.
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| posted on 12/7/06 at 01:06 PM |
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To digress a little;
quote:
Originally posted by jroberts
Caravan?
The curse of motoring!
Where's the fun in peeing in a bucket?
I assume the fun is when you make your wife carry it across the site to empty it !
Tell them about the bent treacle edges!
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spunky
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| posted on 12/7/06 at 01:42 PM |
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hehe...
12 posts before the centrifugal v's centripetal forces came up...
The reckless man may not live as long......
But the cautious man does not live at all.....
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DIY Si
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| posted on 12/7/06 at 03:31 PM |
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Just make sure that each side is capable of carrying 150/200+ kgs and you'll be fine. That way even if it were on the point of rolling ie one
side taking 100kg, the suspension won't collapse. But remember at this point the forces won't be acting vertically through the suspension
unit as it will be turned slightly due to roll.
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Liam
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| posted on 12/7/06 at 04:32 PM |
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quote:
Originally posted by ReMan
quote:
Originally posted by britishtrident
Stop thinking in terms of weight and think in terms of forces.
For example take a trailler or carvan weighing 1 ton.
As already pointed at max cornering speed you get 100% weight transfer to the outside wheel, we will guess max cornering is at 1G.
In 1g cornering for a trailler weighing 1 ton a reaction force of 10kn is generated in the horizontal direction.
Using vector addition add this to the vertical load (also 10kn) and you get a reaction force of 14 kn acting upwards at 45 degrees from the tyres
point of contact.
[Edited on 12/7/06 by britishtrident]
So the answer is yes then!
If you think of the extreme case where the vehicle/trailer was going round a banked corner, or better still a wall of death, then the faster it goes
the "heavier" it will get.
Though obviously a caravan would have tipped over a long time ago.
Can you not use the bolt on indespension units, presumably they are rated with different loadings?
No, the answer is still no . Bt's calc is perfectly correct but only really useful as an indicator of how much work the tyre might have to
do. The vertical component of the force is still only the weight of the trailer, even though the tyre is providing a horizontal reaction force too (I
feel real sorry for this tyre in BTs calc with a 1 tonne trailer cornering 1g ). Only the vertical component is weight - i.e. the spring on this
100% loaded wheel will only compress as if it had the trailers total weight on it, no more. The trailer certainly doesn't gain more downforce
the harder it corners! If you can get it to do that a few F1 engineers might want to hear from you!!
Liam
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skidude88
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| posted on 13/7/06 at 08:40 AM |
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How many seats are inside?
This link might be useful, a little known secret about seats and physics!
http://www.vxronline.co.uk/messageboard/viewtopic.php?t=714
see 1st (none blank) reply by "police_Driver"
[Edited on 13/7/06 by skidude88]
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I love speed :-P
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| posted on 13/7/06 at 08:48 AM |
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quote:
Originally posted by skidude88
How many seats are inside?
This link might be useful, a little known secret about seats and physics!
http://www.vxronline.co.uk/messageboard/viewtopic.php?t=714
see 1st (none blank) reply by "police_Driver"
[Edited on 13/7/06 by skidude88]
Don't Steal
The Government doesn’t like the competition
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iank
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| posted on 13/7/06 at 09:07 AM |
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Well it will lower the CoG by almost a mm*  Must start cleaning my car to improve the aero
*Wild Guess for humorous effect before the mathematicians start on at me
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jono_misfit
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| posted on 13/7/06 at 11:20 AM |
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lol,
"Often I put the rear seats flat, this reduces weight. (Like why you crawl flat across a frozen pond so as not to break the ice)"
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02GF74
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| posted on 13/7/06 at 01:45 PM |
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dammit, why was the thread locked:
could do with more classis like:
The rear seat thing, It is rare that I fold them down, but it has to be said that when folded they remove a bit of weight. Vertical seats exert more
downward force because the energy is focused on a smaller surface area. When horizontal, the weight is spread and so is less per Centimetre squared.
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Rob Palin
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| posted on 13/7/06 at 04:42 PM |
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quote:
Originally posted by spunky
hehe...
12 posts before the centrifugal v's centripetal forces came up...
As a card-carrying certified physist i would have mentioned it earlier but i've been too busy curled up in the foetal position sucking my thumb
and rocking gently backwards & forwards.
You'd think i'd be acclimatised to that sort of thing by now - i work in aerodynamics and everyone keeps talking about suction pulling on
things. Makes me twitch every time.
They really should offer counselling to physics people when they leave uni. Help them fit back into society that bit better
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Guinness
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| posted on 14/7/06 at 12:19 PM |
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Wow that's a top tip on the VXR forum.
I just shaved 2 seconds off my 0-60 time in my tin top. Put the back seats down AND the front seats flat! Adjusted the vanity mirror on the sunvisor
so I could see where I was going and sort of lay down, wow that was loads faster!
Must try it again with the wing mirrors folded in!
Mike
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iank
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| posted on 14/7/06 at 12:22 PM |
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quote:
Originally posted by Guinness
Wow that's a top tip on the VXR forum.
I just shaved 2 seconds off my 0-60 time in my tin top. Put the back seats down AND the front seats flat! Adjusted the vanity mirror on the sunvisor
so I could see where I was going and sort of lay down, wow that was loads faster!
Must try it again with the wing mirrors folded in!
Mike
Have you fitted an exhaust you can get your head in yet - must be worth another second...
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