Pendulum

pplater · 1 Feb 2004, 12:22 (Ref:858793)

This is going to sound weird...

Has there ever been a device that may have been called a pendulum used in touring car racing? it may have had a large weight, (30+kg) and some form of spring system, possibly used to counter the effect of centrifugal force on the car (more even tyre load?)

I heard something once from someone that knew less than i, and i wanted to clarify it.

**Adam43** · 1 Feb 2004, 22:24 (Ref:859528)

I have thought about a device that is basically shifting ballast depending on whether the car was accelerating or braking. It was more of a front-rear thing rather than a left-right thing, but that is a good idea!

Obviously the car would have to be well under the weight limit (although this is quite likely) and generally it is probably better to just get the weight as low as possible, something a mechanism that moves the weight would hinder.

Interesting idea!

pplater · 1 Feb 2004, 22:59 (Ref:859548)

apparently, these things have been created- illegaly.
they are not allowed in any race series i know of, and i want to reasearch them a bit.

imull · 2 Feb 2004, 00:19 (Ref:859596)

i would guess that it comes under the category of ballast and therefore must be fixed in position.

the sorts of weights that would be needed would make it too big to hide i reckon.

suspension isnt really my thing, but in order to make the car lean into a turn, would you not have to get the centre of gravity below the roll centre of the car for this to happen?

As the theoretical ideal for roll centre height is ground level this may be a bit tricky.

avsfan733 · 2 Feb 2004, 06:35 (Ref:859748)

anyone got a good link for explaining roll centers? i am not sure i fully understand the concept

Kid Prozac · 2 Feb 2004, 09:21 (Ref:859847)

When asked I've always defined it as, the point in the vertical plane at which when a lateral acceleration is applied will not cause the body to roll. Now, as the roll centre is nearly always (99.9%) below the CG, this causes the car to roll. If the roll centre is at the CG, no roll occurs. If the roll centre is above the CG, the car leans into the corner.

Thats the easy bit. How you define where the roll centre is, is open to opinion, I know of at least three ways of calculating it, all giving slightly different results.

Try:

http://www.eng-tips.com/viewthread.c...PID=800&page=2

from:

http://www.eng-tips.com/threadminder.cfm?SPID=800

Kid Prozac · 2 Feb 2004, 09:25 (Ref:859851)

Quote:

Originally posted by imull

As the theoretical ideal for roll centre height is ground level this may be a bit tricky.

Not necessarily. With the Formula Student car I'm working on, my front roll centre is 70mm above the ground and the rear a fraction higher and adjustable. The reason for the height is to get a lot of scrub (6mm for +25mm) in suspension movement, so that the tyres are overworked a lot.

However, its horses for courses, F1 will have RC's at or just below ground level, so as to create an initial weight transfer to the inside wheel on corner entry.

imull · 2 Feb 2004, 11:39 (Ref:859945)

my housemate worked on my uni's Formula student car and they had negative ride height values. think it was 7 and 11mm (f/r) below ground level from memory...

it was designed for 4 wheel steer so maybe that had something to do with it. mind you they rolled the car a week before the competition so it was academic anyway lol

we were given a method of drawing lines through the pick up points or something. 2 years ago now and it was hard to stay awake for it then...

Kid Prozac · 2 Feb 2004, 12:07 (Ref:859976)

Quote:

Originally posted by imull
my housemate worked on my uni's Formula student car and they had negative ride height values. think it was 7 and 11mm (f/r) below ground level from memory...

it was designed for 4 wheel steer so maybe that had something to do with it. mind you they rolled the car a week before the competition so it was academic anyway lol

What uni are you at? know of a couple of temas who have rolled their car.

Quote:

we were given a method of drawing lines through the pick up points or something. 2 years ago now and it was hard to stay awake for it then...

Yeah thats the way most people know, and what most books state. Should have stayed awake, its all important stuff

pplater · 2 Feb 2004, 12:48 (Ref:860028)

I think Newcastle, Astralia tried 4WS...
I do not think they raced though.

imull · 2 Feb 2004, 13:06 (Ref:860060)

I am at Swansea Institute for my sins.

I have absolutely zero interest in suspension design. Can do it all, just dont enjoy it.

far rather aerodynamics and structural design like roll cages...

james_williams · 2 Feb 2004, 13:24 (Ref:860080)

Quote:

Can do it all, just dont enjoy it.

???

If you can do it all, you haven't studied it long enough! You can never know it all about parts on a racing car, technology is always moving on!!

The pendulum idea sounds interesting. Might have a look at that! Interesting. Sorry but can't help on any info.

imull · 2 Feb 2004, 14:37 (Ref:860155)

obviously not claiming to be at F1 level or whatever.

was meaning that I understand and can do all the stuff that we have had to so far for Vehicle Dynamics modules. I dont for a minute think that that is the be all and end all of learning about designing a car suspension.

Still doesnt change the fact that it bores me to death

james_williams · 2 Feb 2004, 16:33 (Ref:860256)

Cool.
Yeah...I know what you mean, aero is more interesting!

GolddustMini · 3 Feb 2004, 01:22 (Ref:860895)

u might want to consider the rather scary things that a pendulum might do when exiting a corner and attempting to straighten up the pendulum would still be swinging and as such would upset the balance of the car. it would have to be correctly damped in such a way as to not unsettle the car during the corner but not upsetting it by swinging about manically at every availbale opertunity, surely it would impart some inertia upon the car during direction change as well which could be detrimental

ive heards of weight blocks being moved around by rams before now, but dunno how sucessful that was, all rather complecated to me

it would be pointless in formula student as well, the amount a system like this would weigh would more than likely hamper the vehicle more than it aided it...

Mackmot · 3 Feb 2004, 01:41 (Ref:860912)

I think the problem with a pendulum is that the driver would have to drive a perfect lap everytime. If they were to break traction on the front or rear it would massively exagerate or reverse the effect and make the car completely unpredictable to drive. I think it would be too dangerous for any human driver.

avsfan733 · 4 Feb 2004, 07:43 (Ref:862300)

If the pendulum was reactive to sensor inputs as opposed to programmed based on position of the car over a lap it possibly could work

kingfloopy · 4 Feb 2004, 22:20 (Ref:863257)

The main thing I would be scared of would be undamped oscillation. A series of bumps could make the pendulum go out of control. Then as the driver tries to correct the problem it would only get worse. I would think a pendulum would make a car difficult to handle. It would create weight transfer, but I think that it would change the center of gravity of the car in the corners. The shifting weight may make the car difficult to turn because of the inertia of the pendulum mass.

J.D.

GTV27 · 5 Feb 2004, 03:35 (Ref:863575)

How about shifting mass (ie C of G) only fore and aft to create extra traction under, respectively braking and accelleration via some sort of viscous fluid (to dampen movement) in longtitudinal pipes? The speed of response may be a problem though ?

Side to Side might be hard, but could the the next step if F/R worked.

Why settle for a static C of G when it could be active. After all, we don't just put up with fixed gearing, but have a number of choices to suit a range of circumstances. Similarly, active aero would have been more widespread had not the rules been brought in against it in the 60's. Active weight transfer sounds really interesting.

Mr Lister · 6 Feb 2004, 13:12 (Ref:865392)

Quote:

Originally posted by pplater
This is going to sound weird...

Has there ever been a device that may have been called a pendulum used in touring car racing? it may have had a large weight, (30+kg) and some form of spring system, possibly used to counter the effect of centrifugal force on the car (more even tyre load?)

I heard something once from someone that knew less than i, and i wanted to clarify it.

I read, (but can't remember where

) that Mercedes used a system in the DTM/ITC that had the success ballast mounted on a hydraulic or pneumatic ram which would move the position of the ballast during the course of the race. I don't know whether the ballast moved once, gradually, during the race - to compensate for changing the c of g when burning up the fuel for example - or, if the ballast was continually on the move to give the best dynamics for each corner. I'm unsure of how they could control the ballast to do exactly what they wanted and when if it was the latter though.

Revracing · 6 Feb 2004, 13:23 (Ref:865404)

Help me out here, centrifugal force (or cornering G forces) are derived from the angular speed, radius of curvatature and the mass of the body in motion, in this case the race car, so the mass of the pendulumn is contributing to the cornering forces, I cannot see how it could be used to counter it since it becomes an integral part of the system as soon as it is bolted in.....

Dave Brand · 6 Feb 2004, 14:17 (Ref:865467)

Quote:

Originally posted by Revracing
Help me out here, centrifugal force (or cornering G forces) are derived from the angular speed, radius of curvatature and the mass of the body in motion, in this case the race car, so the mass of the pendulumn is contributing to the cornering forces, I cannot see how it could be used to counter it since it becomes an integral part of the system as soon as it is bolted in.....

There is no such thing as 'centrifugal force'! Inertia forces act tangentially, not radially; if you want a demonstration of this, twirl a weight on a length of string, then let when the string is vertical. The weight will fly off horizontally, not vertically as it would if there were any force acting on it centrifugally.

The forces acting on a vehicle while it is cornering at a steady speed can be broken down into two components, one, the effect of cornering input, acting centripetally (i.e. towards the centre) & one, inertia, acting in the instantaneous direction of travel.

The effect of a pendulum in a corner would be analagous to the effect of a sidecar passenger, who maximises grip my moving to the inside of the bend, thus increasing the load on the wheel which the inertia forces are tending to unload. Of course, the mass of the pendulum would increase the inertia of the vehicle, thus increasing its tendency to go straight on; it's doubtful whether the ability to shift load onto the wheels which are doing less work would provide a net gain.

Revracing · 9 Feb 2004, 11:51 (Ref:868099)

Dave your are completly wrong regarding the non existance of centrifugal force, it is by definition the exact opposite of centripetal force, they both co exist. Your analogy regarding the string actually proves the existance of it, just pick up any A level physics text book for a complete description.
I acept your point about weight distribution but that wasn't what the original thread was about.

Revracing · 9 Feb 2004, 12:06 (Ref:868113)

Ran out of time to add this to my previous post...

You are correct Dave in that when calculating forces of this nature it is Centripetal force that is more important to engineers...

Dave Brand · 9 Feb 2004, 16:34 (Ref:868395)

Quote:

Originally posted by Revracing
Dave your are completly wrong regarding the non existance of centrifugal force, it is by definition the exact opposite of centripetal force, they both co exist.

Ok, let me clarify things. There is NO centrifugal force acting on a rotating body - in this case, a car going round a corner.

I'm sure you're familiar with Newton's Laws of Motion.
Now, as predicted by Newton's first law, the car will go straight on until acted on by an external force, in this case a deflection of the front wheels. This input produces a force component which we can analyse as being at right angles to the instantaneous direction of travel; as the vehicle is now travelling on a circular path, the vector of this force will pass through the centre of the notional circle around the circumference of which the vehicle is travelling, so we can justifiably call it a centripetal force.

Newton's third law tells us that to every action there is an equal & opposite reaction so there must be a reaction to the centripetal force we are generating. However, & crucially, that force, which, as the opposite to a centripetal force we call a centrifugal force, is NOT acting on the car - it's trying to move the track surface. If the coefficient of friction between tyre & track is suddenly reduced, or if the tyre's limit of grip is exceeded, the centripetal force acting on the car will be lost; the car will then, in line with Newton's first law, tend to continue straight on.

Quote:

Your analogy regarding the string actually proves the existance of it, just pick up any A level physics text book for a complete description.

On the contrary, it eloquently demonstrates that there is no centrifugal force acting on the rotating mass. The string applies a centripetal force to the weight; the reaction to that force will be felt at the other end of the string as a radial or 'centrifugal' force. Release the string & the weight flies off tangentially, not radially, which proves that there is NO centrifugal force acting on the weight; on your own assertion, centripetal force & centrifugal force co-exist - remove one & the other can't exist!