Safe Speed Forums

Veering of at a tangent with my flywheel sspinning. "Not rocket science" is one of the two pseudo scientific clichés that really irritate me. The point about rocket science isn't that it is difficult but that the consequences of a small mistake are catastrophic. When of my technicians is dithering about testing some new kit I might say "Switch it on, its not rocket science" meaning that the worst that can happen is a blown fuse rather than the lab going up in flames.

The other is "quantum leap" to mean a major change when a quantum is the smallest possible change. Now just let me accelerate this flywheel to precess me back on topic

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

Mole asked: Incidentally, do you accept that when you rev a car in neutral, the engine rocks slightly? If you do, what do you think makes it do that?
It is the effect of initial inertia. Rather like when one wheel is on tarmac the other on ice, the initial inertial causes both wheels to turn before the ice wheel breaks traction. Difficult to spot (well practically impossible), but it does happen.

I really can’t say anymore, however I have placed a Radio controlled car, on a beam of 4mm thick, on rubber mounts to reduce vibration. The car can not tilt itself off or even show any sign of doing so. I was unable to add additional weight to wheel as I could not balance it effectively, although it still didn’t show any realistic signs. However, I hope to find time tomorrow to construct another test bed and motor that can take varying sizes of flywheels.

I decided to go further and made a pendulum cradle for the car to rest in (wheels in the air) and there is no sign of movement, in forward or reverse (and reverse is as fast as forward). I even added counter a weight to the top of the pendulum to reduce the net weight of the car (which is the equivalent of increasing the mass of the wheel). Hopefully I will film it tomorrow and set up a U-tube account for everyone to view it and also add a clip of me taking a 4x4 airborne – just to show you boys how its done.

Please let me know if you feel I need to modify this working model to make a true and fair result. I can in fact rest my 4x4 on a telegraph pole as it is designed to take it and do a “live” demo. But I really think its time people on here put their theory into practice and produced some video clips.

I have a suggestion for the model car. Let's launch it into space and try to change the attitude with its (momentum) wheels! But we don't need to - one already exists, called Radarsat. It uses an ACS with (among other things) momentum wheels. It's an $800 mil pro gramme which uses electric momentum wheels to change the pitch etc. of an object. If Lucy's model is true to life, it will show the same effect. If it doesn't, her model is broken! All this talk of weightlessness is a side-issue of no importance.

http://directory.eoportal.org/presentations/6093/7384.html




PS: unless there is some strange difference between a satellite and a car? I mean, if one "drove" a 4x4 in space (!) and braked hard with (say) the rear brakes, you'd expect a "nose pitch down", wouldn't you?

Momentum wheels aren't exactly rocket science are they, Abercrombiie?

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

Well I certainly would!

...unless of course it were Lucy's car, which clearly operates to its own unique set of physics laws!

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CSCP Latin for beginners...
Ticketo ergo sum : I scam therefore I am!

Not at all, dcbw. I mean, there are a bunch of equations (that I admit forgot years ago ) that
describe them, but I don't think they were that hard. Maybe they were, but the basic idea of Mole's
analogy is true. When you rev the engine, and it rocks, that's the reaction to the heavy crank spinning
up.

PS: I think I've sort of over-killed this. Sorry. But, you know, that effect is weird, most people would say.
In the experience of the vast majority, it just doesn't make sense that a system can change it's
orientation "from within" via a wheel. Surely it needs something to push against, most would say.
Similarly, one would not automatically assume that a rocket firing into a vacuum could do any good.
Yet there you are... these things seem to happen, eh? It just doesn't crop up that much day to day.

I understand what you are getting at now. You are assuming the rotation of the front and rear wheels balance out round the CoG.

This is not the case.

The rotational force, i.e torque, applied to the CoG is dependant on the distance at which the force is applied to the CoG.

This means the torque applied by the mass of the wheel further from the CoG is greater than that of the mass of the wheel closer to the CoG.

Imagine that instead of a wheel you have a bar running through the hub with a mass on either end, also that the CoG lies on a line between the hubs and equally distant. If you stop the bars when are in line with the axis between the hubs the masses furthest from the CoG will apply a torque greater than the masses closest to the CoG therefore there will be a net force trying to rotate the 'vehicle' around the CoG.

But wheels are not masses on the ends of rods are they? Well yes they are as far as the physics goes, just hold that thought for a moment.

Lets stop the wheels with the rods at say 45 degrees.

You now draw a line between the centre of each mass and the CoG, the force applied by each mass has a vector perpendicular to the rod they are connected to. This can be resolved into two components, one perpendicular to the line through the mass and CoG and one parallel with it. The perpendicular force is what causes the rotational torque around the CoG.

Now draw lines through the CoG and tangential to the circle described by the spinning 'wheels', the points at which these lines touch the 'wheels' are where the force applied to the CoG by the wheel changes direction. You will notice that the arc the masses describe while capable of applying a torque in one direction is greater greater than the other direction, further more as this arc's path occurs at a greater distance from the CoG the torque applied is also greater for any position along its length.

So, weights on bars are not wheels are they? Again, yes they are.

Lets add another bar and masses to each hub at right angles to the first, it is pretty easy to see that for any given position of the 'wheel' the resultant torque is always going to be in one direction. Add two more bars and masses to each hub, evenly spaced, in fact keep doubling the bars and masses and eventually the masses touch and we have a spoked wheel.

The torque applied about the CoG will in general be opposite to the direction of acceleration of the wheels, do not forget deceleration is just acceleration with a negative sign.

If the CoG is not equally spaced between the hubs or in line with the hubs the effect will still occur. Without doing the maths I cannot be certain, but in line at equal spacing is probably where you get the maximum torque.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

It's not a showstopper. One could alter the pitch by reving just the back wheels, or using the
handbrake to slow the back wheels.

I got the impression Lucy thought the front and rear would cancel as opposite forces whereas they are additional.

I just worked on the instrument packages not the noisy bits, specifically the data and tracking sensors for the Silex package.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

Just briefly as I am getting brassed ogg at being told on another thread by someone who has never heard of a G-Sensor, that I am making things up. What a muppet!

The key is reaction, in the air no resistance, so no reaction. It is quite right that Chinook helicopter's rotors rotate in opposite directions to cancel the reactions out - but that is because the rotors have very high resistance - so much that it lifts the thing in the air!

Car wheels don't - that's the difference. I appologise for simplifing my analysis of reactions and as it reads, in fact it is wrong. The reactions I was referring to was initia inertia, which acts on the C of G and is so small is insignificant in automotive dynamics in the case of a flying rally car.

To settle the matter I suggest that you balance a radio controlled car on a narrow beam, or construct a pendulum cradle and see what happens then. I am not argueing with all peoples observations - they are correct. But they all rely on reaction to resistance somewhere.

Air resistance is not required, you would get the same effect in a vacuum, technically it would be greater as there would be no air resistance stopping the rotation of the car.

The Chinook is balancing different forces, you are correct in that it the reaction to pushing air that is being balanced.

If you could run a Chinook in a vacuum either suspended from its CoG or in freefall then you would still need both rotor to prevent rotation of the body. Only however while they are being accelerated/decelerated. If the blades of one rotor could be released to fly off from the rotor head the Chinook would not rotate unless the remaining rotor changed its speed.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

I always took that to mean a change that did not have to progress through intermediate stages similar to a change in energy level in Quantum mechanics.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

To quote Homer Simpson:

"This is brain surgery, not rocket science!"

That is the key issue, AFAICS.

That SILEX stuff looks interesting. Were you at Darmstadt?

It certainly does. Does the inter satellite link use modulated free space lasers?

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

I see this thread started before I joined the board!





Not if you're riding a motorcycle.

So if you encounter an unexpected obstacle around a blind corner, you believe that "best practice" is to hit it then?

_________________
CSCP Latin for beginners...
Ticketo ergo sum : I scam therefore I am!

That's one option. Another is to drop the bike before you hit a wall or go under a truck. But once
you brake and loose it, all control is gone.

So if we follow this belief (as was pointed out by the great man himself on page one of this thread) then there is NO speed at which a motorcycle can safely negotiate a blind corner?

_________________
CSCP Latin for beginners...
Ticketo ergo sum : I scam therefore I am!

I don't know if the Great Man was a biker, but there is no such thing as
a blind corner. You can always see partly into it. That gives you some
space, because a bike is narrow, to pull it up in an emergency. As you
pull it up, you brake. You don't brake much while it's keeled over.

The idea with tight corners is to keep enough margin to pull it up,
and brake. If you have to brake in the bend, be very gingery with
the lever - or you're dead sure to get gravel rash from a diesel spill!
I know about that...

PS: you might have a bit of luck with the back brake, instead...
but you have to think fast.